Prof.Dr. Mohamed Hemida Abd-Alla (Egypt, Assuit University)

Abstract: Rotten onion bulbs were collected from different markets in Assuit governorate and screened for the presence of phytopathogenic bacteria using yeast extract-dextrose-calcium carbonate medium and King's medium B. Thirty-five bacterial isolates were recovered from 15 onion bulb samples. Twenty-five bacterial isolates were classified as putative Pseudomonas aeruginosa. Ten other unidentified bacteria were isolated at the same time and designated as Gram negative bacteria and nonflourescents. None of these bacteria have been reported as being pathogenic and it is likely that these other bacteria were present as concomitant/commensal bacteria. The causal agent of onion bulb rot was identified as Pseudomonas based on phenotypic characteristics. One representative isolate of these has been further identified as a Pseudomonas aeruginosa by sequencing of the 16S rRNA gene. The bacteria have the ability to grow in a temperature range of 4–43°C, with optimal growth at 37°C. Virulence of the Pseudomonas aeruginosa was also confirmed by the production and secretion of a large variety of enzymes capable of degrading the complex polysaccharides of the plant cell wall and membrane constituents. Scanning electron micrographs indicated that the Pseudomonas aeruginosa isolates were able to abundantly colonize the internal tissue of fleshy scales of onion bulbs. The virulence of the pathogen may be attributed to biofilm formation on the plant cell wall via fibrous materials as revealed by scanning electron microscopy as well as high activity of proteases, lipase, pectinases, and alkaline phosphates. This is the first evidence showing that a Pseudomonas aeruginosa strain E can cause soft rot of onion bulbs.

Abstract: Bacterial contamination of fresh tomato fruits is of great concern. From naturally infected tomato fruits showing dark brown irregularly shaped spots, 36 bacterial isolates were recovered and identified on phenotypic characteristics and sequences of the gene encoding the 16S rRNA. Five isolates showing spots on tomato fruits in the pathogenicity test with healthy tomato fruits belong to the genus Serratia on the basis of phenotypic characteristics. One representative isolate of these has been further identified as a Serratia rubidaea by sequencing of the 16S rRNA gene. This is the first evidence showing that a S. rubidaea strain can cause spots on tomato fruits. Virulence of the S. rubidaea was also confirmed by the production and secretion of a large variety of enzymes capable of degrading the complex polysaccharides of the plant cell wall and membrane constituents. Nineteen bacterial isolates of the 36 did not induce any spot symptoms in a pathogenicity test on artificially infected tomato fruits although these are known as phytopathogenic bacteria. Five of these 19 bacterial isolates were identified as Ralstonia species on the basis of biochemical tests. Sequencing of the 16S ribosomal gene of one representative isolate revealed that the isolate is closely related to Ralstonia solanacearum. Six isolates of the 19 were related to Xanthomonas vesicatoria on the basis of biochemical tests and eight were related to the Enterobacteriaceae. One representative isolate of the Enterobacteriaceae could be identified by the 16S rRNA gene as Enterobacter cloacae subsp. dissolvens. The 12 other strains were related to Proteus mirabilis based on the 16S RNA gene sequence of one representative isolate. The isolates related to P. mirabilis did not produce any symptoms on artificially infected tomato fruits. The nucleotide sequences of S. rubidaea strain E9, E. cloacae strain E23, P. mirabilis strain E11, and R. solanacearum strain E15 have been deposited in the GenBank nucleotide sequence database under accession numbers HM585373 to HM585376

Abstract: L.) by three fermentation stages. A facultative anaerobe, Escherichia coli EGY was used in first stage to consume O2 and maintain strict anaerobic conditions for a second stage dark fermentative H2 production by the strictly anaerobic Clostridium acetobutylicum ATCC 824. Subsequently, a third stage photofermentation using Rhodobacter capsulatus DSM 1710 has been conducted for the H2 production. The maximum total H2 yield of the three stages (7.8 mol H2 mol1 sucrose) was obtained when 5 g L1 of sucrose was supplemented to fermentor as rotten date fruits. A maximum estimated cumulative H2 yield of the three stages (162 LH2 kg1 fresh rotten dates) was estimated at the (5 g L1) sucrose concentration. These results suggest that rotten dates can be efficiently used for commercial H2 production. The described protocol did not require addition of a reducing agent or flashing with argon which both are expensive.

Abstract: Common bean seed lots collected from different seed dealers and Malawii agriculture station were screened for the presence of Xanthomonas axonopodis pv. phaseoli. In the laboratory the pathogen was isolated following the routine laboratory assay method, i.e. direct plating method using yeast extract-dextrose-calcium carbonate agar medium (YDC). Yellow, convex, mucoid colonies of Xanthomonas were consistently isolated on YDC from seed samples. The presumptive pathogen was confirmed by isolation on semiselective medium, such as mTBM and MD5A. Further, the pathogen was confirmed by biochemical, physiological and, finally, the pathogenicity tests. Five samples out of seven were positive for Xanthomonas. The isolates were found to cause common blight of 3-week-old common bean plants by 7 d after inoculation. Bacteria with the same characteristics as those inoculated were re-isolated from the infected plants.

Abstract: Tomato fruits and seed lots were screened for the presence of Xanthomonas vesicatoria and Ralstonia solanacearum. Yellow colonies of Xanthomonas vesicatoria and white colonies of Ralstonia solanacearum were consistently isolated on yeast extract-dextrose-calcium carbonate agar medium (YDC) from diseased fruits and seed samples. This was confirmed by isolation on semi-selective medium such as Tween B for Xanthomonas and triphenyltetrazolium salt (TTC) medium for Ralstonia solanacearum followed by biochemical tests. The four isolates belonging to Xanthomonas vesicatoria and Ralstonia solanacearum were used to inoculate a local tomato variety. The isolates were found to cause yellowing and wilting of 2-weeks-old seedlings by 8–14 days after inoculation and by 4 weeks all plants had wilted and completely died. Bacteria with the same characteristics as those inoculated were reisolated from the infected plants. Uninoculated plants remained healthy.

Abstract: Two strains of Bradyrhizobium japonicum wereevaluated with five commercial cultivars of soybean(Clark, Crauford, Davis, Centaur, and Nessen) and onehypernodulating mutant NOD1-3. The hypernodulatingNOD1-3 produced 30–50 times more nodules thancommercial cultivars either inoculated with B.japonicum strain USDA 123 or RCR 3409. The currentexperiments were extended to determine if therestricted nodulation of commercial cultivars could be overcome by grafting them to a hypernodulated shoot (NOD1-3). Grafting of NOD1-3 shoots to Clark and Davis roots induced hypernodulation on roots of Clark and Davis but did not enhance nodulation when grafted onto the roots of Crauford, Centaur, and Nessen. The shoots of Clark, Davis, Centaur and Nessen significantlyinhibited nodule formation on the root of NOD1-3,while Crauford shoots did not alter nodule formationon the roots of NOD1-3 as compared with self-grafts ofNOD1-3. It appears that the shoot of NOD1-3 has theability to alter autoregulatory control of nodulationof Clark and Davis cultivars, but did not withCrauford, Centaur and Nessen. The results suggestedthat the regulation of nodulation in soybean cultivarsClark and Davis is controlled by the shoot factors,while the Crauford was root controlled.Reciprocal-grafts between NOD1-3 and Centaur or Nessenindicate that both shoot and root factors involved inregulation of nodulation and the regulation ofnodulation did not depend on bradyrhizobial strains. Isoflavonoid analyses from extracts of grafted plantsshowed that NOD1-3 shoots had markedly higher rootisoflavonoid concentrations in roots of both Clark andNOD1-3. The shoot control of hypernodulation may becausally related to differential root isoflavonoidlevels, which are also controlled by the shoot. Thecurrent work was extended to investigate the effect ofapplication of an isoflavonoid (daidzein) on nodulationand nitrogen fixation of soybean cultivars Clark andCentaur as well as in vitro growth of Bradyrhizobium japonicum. Application of theisoflavonoid (daidzein) significantly enhanced thenodulation and nitrogenase activity of Clark but notof Centaur indicating that this character is notrelated to isoflavonoids. Therefore, autoregulationin Clark and Centaur plants may be separate events inlegume-rhizobia symbiosis and regulated by differentkinds of signals. Addition of daidzein to yeastmannitol broth medium promoted the growth of B.japonicum strain USDA 123 and RCR 3409. It seemsthat this compound is able to help the nodulation ofsoybean cv Clark by a Bradyrhizobium strain. Understanding the signaling pathways between rhizobiaand their host plants may allow modifications of thisinteraction to improve symbiotic performance.

Abstract: Faba bean cv. Giza 3 was grown in hydroponic cultures and inoculated with Rhizobium leguminosarum bv. viceae TAL 1402. Salinity levels at 40, 80 and 120 mM NaCl were applied at transplanting and inoculation. The highest level of salinity level (120 mM) significantly suppressed nodulation, nitrogenase activity and plant growth. This salinity level also significantly decreased the concentrations of macro and micro nutrients in faba bean leaves. X-ray microanalyses of nodules under high levels of NaCl indicate that Ca, K, Mg and S were lower in the infected and uninfected cells of faba bean nodules than control ones, whereas, Na and Cl were higher. Nitrogen content of nodules was significantly higher in plants treated with high salinity levels than nonsalinized ones. However, the N content of shoots was lower than the controls. The inhibition of nitrogenase activity at high levels of salt stress could be explained in terms of product inhibition of the enzyme as an efficient feedback regulation mechanism. The X-ray microanalysis results revealed that the N export from nitrogen-fixing cells is sensitive to salinity and is controlled by element distribution in nodules.

Abstract: Eighty-four microbial isolates were tested for their ability to produce siderophores using four chemical assays. From these isolates, 42 were strongly or moderately positive on chrome-azurol S assay (CAS). However, they showed no reaction with phenolates assay

Abstract: Coculturing of eight rhizobial strains (Bradyrhizobium japonicum USDA 110, USDA 3447, RCR 3407, RCR 3442, Rhizobium meliloti TAL 1372, TAL 1373, R. leguminosarum biovar viceae RCR 1001, and RCR 1044) and five rock-phosphate-solubilizing fungi (Aspergillus egyptiacus, A. flavus, A. niger, A. ochraceus, and Penicillium citrinum) was tested on yeast extract-mannitol agar. B. japonicum strains USDA 110, USDA 3447, RCR 3442, R. leguminosarum biovar viceae RCR 1001, and RCR 1044 grew successfully in cocultures with the tested fungal species in yeast extract-mannitol agar without antagonism. Among these fungi, A. niger showed the highest potentialities to solubilize rock- phosphate at all incubation temperatures examined (15, 28, 38, and 42°C), and phosphate dissolution maximized at 28°C. Survival of Rhizobium/Bradyrhizobium strains and the best rock-phosphate-solubilizing fungus (A. niger) was evaluated monthly in four carrier materials (Peat, wheat bran, sugarcane baggase, and wheat straw) at 28 and 38°C. The number of colony-forming units recovered on agar plates for all cocultured microorganisms was the highest with peat as a carrier, followed by bran and sugarcane baggase. On the other hand, survival of cocultured microorganisms strongly reduced in wheat straw. Survival of all microorganisms was the best at 28°C. Cocultures of B. japonicum USDA 3447/A. niger and R. leguminosarum RCR 1044/A. niger were the more tolerant for storage conditions whereas the number of colony-forming units in cocultures of B. japonicum USDA 110/A. niger and R. leguminosarum RCR 1001/A. niger was strongly reduced. Peat or bran inoculants of R. leguminosarum RCR 1044/A. niger and B. japonicum USDA 3447/A. niger significantly increased dry matter yield, nitrogen (N) and phosphorus (P) contents of faba bean and soybean, respectively, when grown in alkaline soil amended with rock-phosphate.

Abstract: Effects of the pesticides Afugan, Brominal, Gramoxone, Selecron and Sumi Oil on growth, nodulation and root colonisation by arbuscular mycrrhizal (AM) fungi of the legumes cowpea (Vigna sinensis L.), common bean (Phaseolus vulgaris L.) and Lupin (Lupinus albus L.) were determined. The growth of all plants was inhibited by pesticide application, but this effect varied with the pesticide and plant species. Nodule formation was significantly inhibited in cowpea after 20 days of planting by all pesticides tested. Following the initial decrease, there was recovery from the inhibitory effects at 40 and 60 days after planting. Although the number of nodules on common bean and lupin did not differ from control at 20 days after planting, differences were evident during the later stages of plant growth. The pesticides significantly inhibited AM root colonisation and the number of spores in all legumes, but on the other hand, spore formation was stimulated in pesticide-treated cowpea 60 days after planting. The accumulation of N, P and K in pesticide-treated plants was lower than in control plants. Growth and nutrient status of the legumes varied with nodulation and AM colonisation. The results suggest that pesticides affect plant growth, Rhizobium/Bradyrhizobium and AM fungi at different stages of plant growth and effects varied with pesticide and plant species.

Abstract: The structure of N2-fixing nodules of faba bean (Vicia faba L.) was investigated by means of light and electron microscopy to determine possible pathways for metabolite movement. The central infected zone is enclosed by a cortex, which is composed of a loosely arranged outer part and a densely packed inner part. Both are separated by the nodule endodermis, which borders on the root endodermis and continuously envelopes the entire nodule interior, with the exception of the apical meristematic region. Vascular bundles, located peripherally within the inner cortex, are surrounded by another endodermal layer. Radial cell walls of both nodule and vascular endodermis are incrusted and form Casparian bands. Additionally, all endodermal cells are coated by suberin lamellae. These modifications may prevent an apoplastic loss of solutes from the enclosed tissues, and require a symplastic metabolite passage. This is supported by high plasmodesmatal frequencies found between vascular endodermis and inner cortex. Within vascular bundles, transfer cells adjacent to xylem elements may play a role in xylem loading. The central infected tissue contains uninfected cells, possibly representing a symplastic continuity. These cells may form a preferred metabolite pathway since plasmodesmata are extremely sparse between infected cells. The low number of uninfected cells in the central tissue of V faba nodules favors an additional apoplastic pathway

Abstract: The present study was made to isolate and assess some physiological characteristics of root nodule-colonizing fungi. During this study, 17 fungal species were isolated from root nodule samples taken from faba bean plants (Vicia faba L.) collected from different sites at Assiut area (Egypt). The growth of faba bean plants in pots was significantly promoted by soil inoculation with most fungi. Growth was checked in pots with inocula of Cladosporium cladosporioides, Fusarium moniliforme, F: oxysporium, F solani, Macrophominia phaseolina and Rhizoctonia solani which were added separately. All growth-promoting fungi were capable of producing cellulase, pectin lyase, polygalacturonase, protease, urease, amidase, acid phosphatase, alkaline phosphatase and arylsulfatase in growth medium supplemented with the corresponding substrates. Four fungal species, Aspergillus awamori, A. flavus, Penicillium chrysogenum and Trichoderma koningii showed the highest rates of enzyme formation. The effect of the addition of six trace elements to the growth media at 30 micromol/ml on enzyme production revealed some dependency on species, enzyme and metal ion. Cd2+, Hg2+ and Zn2+ generally inhibited enzyme activity. Cu(1+), Fe3+ and Al3+ showed a stimulatory effect. Fungicides (afugan and tilt) and herbicides (brominal and fusilade) at 50 ppm generally promoted enzyme activity, but insecticides (kelthane and fenvalerate) caused some inhibition to enzyme activities. Salinization of the growth media with NaCl strongly inhibited the enzymatic activity of all fungi at concentrations between 0.5 and 1.5%.

Abstract: Bean seedlings 7 days old were left to grow for 10 days in hydroponic cultures containing 0, 5, 15 ppm Nickel as NiCl2 Calcium was added (1 mM or 5 mM) in combination with Nickel. Growth criteria, mineral contents, nickel distribution and metal-binding proteins were investigated. The fresh and dry weights of roots and shoots were sharply reduced especially at the higher dose (15 ppm Ni+2). The content of some elements (K, Na, Ca, Mg and Mn) of roots and shoots were variably affected in presence or absence of calcium. Nickel was accumulated in roots more than in shoots. Fractionation of roots and shoot of bean plants revealed that the accumulation Nickel was in the insoluble form (cell wall), while the remainder (the soluble form) was bound to proteins in the form of metalloproteins. Calcium reduced the toxic effect of nickel especially at the low dose (5ppm). It was found that calcium reduced the uptake of nickel by roots and enhanced the synthesis of proteins, which form and metal-binding proteins.

Abstract: The effect of six Bradyrhizobium sp. (lupin) strains (WPBS 3201D, WPBS 3211D, USDA 3040, USDA 3041, USDA 3042 and CB 2272) and Fe supply on nodulation, N2-fixation and growth of three lupin species (Lupinus termis, L. albus and L. triticale) grown under Fe deficiency in an alkaline soil, were examined in sterilized and non-sterilized pot experiments. When inoculated with USDA 3040, 3041, 3042 and CB2272 without Fe addition, the three lupin species had a very low nodule number and mass, low shoot and root dry matter accumulation and lower N yield. However, inoculation with WPBS 3201D and 3211D without Fe treatments increased all these parameters substantially. The ability of WPBS 3201D and 3211D to form nodules on the three lupin species under conditions of Fe stress could be attributed to their ability to scavenge Fe from Fe-deficient environments through their siderophore production. Addition of Fe to the other four strains significantly increased nodulation and N2-fixation of the three lupin species, indicating that the poorer nodulation and N2-fixation of these strains in the absence of Fe, resulted from a low ability to obtain Fe from alkaline soils. Bradyrhizobium strains WPBS 3201D and 3211D were superior to the other four strains in terms of promoting greater nodulation, N2-fixation, plant growth and N accumulation of L. termis and L. albus. However, the other four strains were more efficient in symbiotic association with L. triticale. The greater variations in nodule efficiencies (specific nitrogenase activity) under different levels of Fe supply could be attributed to the quantities of bacteroid protein and leghaemoglobin in the nodules. The results suggested that Bradyrhizobium (lupin) strains differ greatly in their ability to obtain Fe from alkaline soils, and that the selection of bradyrhizobial strains which are tolerant of Fe deficient soils could complement plant breeding for the selection of legume crops for Fe-deficient soils. Key words Acetylene reduction assay - Bradyrhizobium spp. - Iron deficiency - Lupinus spp. - Nodulation

Abstract: The effect of sewage sludge application to a desert soil on nodulation, nitrogen fixation and plant growth of faba bean (Vicia faba cv. Giza 1), soyabeans (Glycine max cv. Clark) and lupin (Lupinus albus cv. Marita) was investigated in a pot experiment under greenhouse conditions. Nodulation, nitrogenase activity and plant growth of faba bean, soyabeans and lupin were significantly increased by moderate application rates of sewage sludge (20 and 30%, w/w). The decisive effect caused by application of sewage sludge on legume growth was the promotion of nodulation and subsequent nitrogen fixation. At an application level of 30% (w/w), nodulation was increased by 55%, 96%, and 171% for faba bean, soyabeans and lupin, respectively, compared with controls. Conversely, at high application rates (40 and 50%) sewage sludge significantly inhibited nodulation, nitrogen fixation, dry matter accumulation and nitrogen yields of faba bean and soyabeans. Again, inhibition of nodulation by high amounts of sludge was the decisive process responsible for low nitrogen fixation and dry matter production of legume plants. At 50% application rate, sewage sludge decreased nodulation by 62%, 79% and 29% for faba bean, soyabeans and lupin, respectively, compared with controls. Plant analysis indicated that the inhibitory effect of sewage sludge at high application rates was most probably due to a toxic (noxious) effect of heavy metals (Cu and Zn) on the microsymbiont rather than on host plants. It is concluded that sewage sludge at low application rates may significantly improve legume growth on desert soils

Abstract: Two strains of Bradyrhizobium japonicum were evaluated with ®ve commercial cultivars of soybean (Clark, Crauford, Davis, Centaur, and Nessen) and one hypernodulating mutant NOD1-3. The hypernodulating NOD1-3 produced 30±50 times the number of nodules of commercial cultivars either inoculated with B. japonicum strain USDA 123 or RCR 3409. Grafting of NOD1-3 shoots to Clark and Davis roots induced hypernodulation on roots of Clark and Davis but did not enhance nodulation when grafted onto the roots of Crauford, Centaur, and Nessen. In contrast, the shoots of Clark, Davis, Centaur and Nessen signi®cantly inhibited nodule formation on the root of NOD1-3. However, Crauford shoots did not alter nodule formation on the roots of NOD1-3 as compared with self- grafts of NOD1-3. It appears that the shoot of NOD1-3 has the ability to alter autoregulatory control of nodulation of Clark and Davis cultivars, but not of Crauford, Centaur and Nessen. The results suggest that the regulation of nodulation in soybean cultivars Clark and Davis is controlled by the shoot factors, while the Crauford was root controlled. Reciprocal grafts between NOD1-3 and Centaur or Nessen indicate that both shoot and root factors are involved in regulation of nodulation. The results suggested that the regulation of nodulation did not depend on bradyrhizobial strains. The shoot control of hypernodulation may be causally related to di€erential root iso¯avonoid levels, which are also controlled by shoot. Application of daidzein signi®cantly enhanced the nodulation and nitrogenase activity of soybean cv. Clark. Root control of restricted nodulation of soybean cv. Centaur did not respond to the addition of daidzein in nutrient solution indicating that this character is not related to iso¯avonoids. Therefore, autoregulation in Clark and Centaur plants may be separate events in legume±rhizobia symbiosis and regulated by di€erent kinds of signals.

Abstract: SixBradyrhizobium (lupin) strains were evaluated for their ability to produce siderophores using four chemical assays. Two strains gave positive reactions with chrome azurol S assay (CAS) and produced hydroxamate-type siderophores. The other four strains gave negative results for siderophore production using the four assays. Generation time, growth yield and hydroxamate production of one strain (WPBS 3201 D) were affected by the iron concentration of the culture medium and the previous culture history of the cells. Resuspension of washed cells grown previously in media supplemented with 0 and 20 μmol/L Fe into differing iron regimes (0, 0.5, 1, 2, 4, 8, 10, 15 and 20 μmol/L Fe) suggest that the extent of hydroxamate production depended on the growth history of the cells. Cells pregrown in 20 μmol/L Fe produced a high amount of hydroxamates compared with cells pregrown in iron-free medium when resuspended in medium containing up to 4 μmol/L Fe. Cells pregrown in 20 μmol/L Fe were more sensitive to iron repression than those pregrown in 0.5 μmol/L Fe. Mannitol was the best carbon source for siderophore production. Siderophore synthesis was inhibited by 4-chloromercuribenzenesulfonic acid, 2,4-dinitrophenol, sodium azide and MgCl2 suggesting that an energized membrane and a mercapto group are essential and required for hydroxamate synthesis in strain WPB5 3201 D

Abstract: Soil salinity is a major limitation to legume production. We evaluated specific soybean [Glycine max (L.) Merr.] genotypes to identify a salt-tolerant soybean-Bradyrhizobium system, and to determine by grafting experiments if the scion or the root was responsible for salt tolerance. The effects of three levels of salinity (0, 30, and 60 mM NaCl) on nitrogenase activity (acetylene reduction), nodule number, nodule dry matter, and growth of four soybean genotypes (Williams 82, PI 416937, DR-1 [an Egyptian cultivar], and NOD1-3 [a hypernodulating mutant selected from Williams]) were investigated in hydroponic cultures and growth chamber environments. Salt stress significantly inhibited nitrogenase activity, nodule number, and dry matter accumulation per plant of all four cultivars. The detrimental effects of salinity on nodulation parameters and dry matter accumulation were most pronounced for NOD1-3 and Williams 82, intermediate for DR-l, and less marked for PI 416937. Self-grafted NOD1-3 plants showed 50 to 62% inhibition in nodulation responses (activity, number, mass) while grafting of P1416937 scions to NOD1-3 roots resulted in less than 7% inhibition by salt. Nodule number on PI 416937 roots was greater when grafted to NOD1-3 scions (relative to self-grafted PI 416937 plants), confirming a shoot role in autoregulation of nodule number. Conclusions are that shoot factors are of primary importance in determining salt-tolerance of the PI 416937 genotype and that hypernodulation expression in the mutant is negatively affected by salt treatment.

Abstract: Twenty-oneRhizobium andBradyrhizobium strains were testedin vitro against the mycelial growth of three pathogenic fungi on solid and liquid media. All tested rhizobia and bradyrhizobia significantly suppressed the growth of the three soil-borne root-infecting fungi (Fusarium solani, Macrophominia phasolina andRhizoctonia solani) either in the absence or presence of iron. This indicates that the siderophore played a minor role in the biocontrol potential ofRhizobium andBradyrhizobium against pathogenic fungi. Pot experiments revealed that the numbers of propagules causing disease after 4 weeks of planting varied with species and host plant. The three most activeRhizobium andBradyrhizobium strains (R. leguminosarum bv.phaseoli TAL 182,B. japonicum TAL 377 andBradyrhizobium sp. (lupin) WPBS 3211 D) tested under greenhouse conditions for their ability to protect one leguminous (soybean) and two non-leguminous (sunflower and okra) seedlings from root rot caused byFusarium solani, Macrophominia phaseolina andRhizoctonia solani provided significant suppression of disease severity compared with nonbacterized control in both leguminous and non-leguminous seedlings.Bradyrhizobium sp. (lupin) WPBS 3211 D provided the lowest degree of resistance against all the tested pathogens with all host plants

Abstract: Seeds of three species of lupine (Lupinus termis, L. triticale andL. albus) were tested to determine if the seed contains diffusable substances toxic to bradyrhizobia.L. albus seeds were less toxic to bradyrhizobia, followed byL. triticale. Six strains ofBradyrhizobium were evaluated for their resistance to the toxic substances in lupine seeds. Zones of growth inhibition were determined on yeast-mannitol-agar medium surrounding surface-sterilized seed. The effect of surface sterilization of seeds by different chemical treatments on seed toxicity was assessed. Seeds soaked in water for 1 h before placing on agar surface significantly decreased the inhibition zone. Also, the effect of soaking seeds in water for 4 h before planting and inoculation on nodulation, nitrogen fixation and plant growth were investigated. Addition of seed diffusate to soaked seeds significantly decreased nodulation and plant growth. Autoclaving the seed diffusate had no effect on the toxicity of the seed diffusate. Addition of the absorbent polyvinylpolypyrrolidone (PVPP) to seed diffusates significantly decreased the inhibitory effect of seed diffusate on nodulation and plant growth. Seed diffusate substances were water-soluble, heat-stable and partially bound to PVPP.

Abstract: Seeds of three species of lupine (Lupinus termis, L. triticale andL. albus) were tested to determine if the seed contains diffusable substances toxic to bradyrhizobia.L. albus seeds were less toxic to bradyrhizobia, followed byL. triticale. Six strains ofBradyrhizobium were evaluated for their resistance to the toxic substances in lupine seeds. Zones of growth inhibition were determined on yeast-mannitol-agar medium surrounding surface-sterilized seed. The effect of surface sterilization of seeds by different chemical treatments on seed toxicity was assessed. Seeds soaked in water for 1 h before placing on agar surface significantly decreased the inhibition zone. Also, the effect of soaking seeds in water for 4 h before planting and inoculation on nodulation, nitrogen fixation and plant growth were investigated. Addition of seed diffusate to soaked seeds significantly decreased nodulation and plant growth. Autoclaving the seed diffusate had no effect on the toxicity of the seed diffusate. Addition of the absorbent polyvinylpolypyrrolidone (PVPP) to seed diffusates significantly decreased the inhibitory effect of seed diffusate on nodulation and plant growth. Seed diffusate substances were water-soluble, heat-stable and partially bound to PVPP.

Abstract: Identification of commonality of nodulation control among legumes will facilitate progress in improving symbiotic N2 fixation in agricultural systems. Interspecies grafts between soybean [Glycine max (L.) Merr] and mung bean (Vigna radiata L.), or soybean and hyacinth bean (Lablab purpureus L.), were made to evaluate whether a common translocatable signal controls expression of hypernodulation among legume species. Grafting of a ‘NOD1-3’ (hypernodulating soybean) shoot to roots of mung bean or hyacinth bean resulted in hypernodulation, a 4.1-fold increase in nodule number for mung bean, and a 2.7- to 5.5-fold increase (depending on bacterial strain) in nodule number for hyacinth bean, relative to self-grafted mung bean or hyacinth bean, respectively. ‘Williams 82’ shoots doubled nodule number when grafted to mung bean roots, but had no effect on nodulation when grafted to hyacinth bean roots. Symbiotic Nz fixation (as measured by nitrogen accumulation in the plant) by nodulated mung bean roots was enhanced by 67% when grafted to Williams 82 and by 78% when grafted to NOD1-3 soybean shoots, compared with self-grafted mung bean plants. Grafting soybean shoots to hyacinth bean roots positively affected symbiotic N2 fixation (9–40% depending on bacterial strain), but the magnitude was less than observed when mung bean roots were grafted to soybean shoots. It was concluded that control of hypernodulation expression by a shoot-transmissible factor is common among soybean, mung bean, and hyacinth bean. Seed were obtained from reciprocal grafts between soybean and mung bean to test for bacterial specificity for infection and nodule development. Seedling progeny from the reciprocal mung bean-soybean grafts were not altered in terms of bacterial specificity for nodulatiou.

Abstract: This study was performed to evaluate the ability of cellulolytic fungi and wheat straw incorporation to improve the nodulation, growth and nitrogen status of fenugreek grown in saline soils. NaCl addition to the growth medium at rates of 0.5 and 1% strongly decreased the enzymatic activity of the ten tested moulds. Three of these fungi, Aspergillus niger, Chaetomium globosum and Trichoderma harzianum, showed the highest enzymatic activity. The three moulds have the ability to degrade straw in the presence of NaCl and T. harzianum was the best straw degrader. Inoculating the plants with Rhizobium meliloti strain TAL1373 and cellulolytic fungi slightly promoted nodulation, growth and nitrogen accumulation when plants were grown with the addition of 0.5% NaCl when compared to plants inoculated with R. meliloti alone. However, application of wheat straw with cellulolytic fungi significantly enhanced growth, nodulation and nodule efficiency at 0.5 and 1.0% salinity. The greatest values of nodulation and growth parameters were obtained with a straw-Trichoderma harzianum combination. Cellulolytic fungi and wheat straw increased the concentration of Ca, Mg and K in the shoots and roots of plants. The increase in dry matter production and N content was mainly due to improved N2 fixation reflected by enhanced formation and growth of nodules as well as nitrogenase activity.

Abstract: The effects of application of combined nitrogen fertilizer (ammonium nitrate or urea) on root-hair infection and nodulation of four grain legumes were studied. Young roots of each legume were inoculated with their compatible rhizobia. The application of the two forms of combined N either at the early stages of plant growth and/or at the time of nodule formation depressed root-hair curling, infection and nodulation. Infection of hairs on the primary roots was more sensitive to the N fertilizer than hair infection of secondary roots in bothVicia faba andPisum sativum. The nodule number and total fresh mass of the four legumes were drastically affected by fertilizer application. The combined N added both at early and at later stages significantly reduced the nodulation ofV. faba, Phaseolus vulgaris andVigna sinensis. The inhibitory effect of urea on nodulation ofP. sativum was only observed when the fertilizer was applied at the late stages of plant growth. It is concluded that, although the nodulation of the four legumes was suppressed by combined N, the initial events ofRhizobium-legume symbiosis (infection of roots and nodule initiation) are more sensitive to combined N than the stages after nodule formation.

Abstract:

Abstract: Three-week-old nodulated faba bean plants were subjected to two levels of water stress (0.5 and 0.25 field capacity; soil water content of 20 and 10%) for five weeks. Half of the stressed plants was treated with potassium chloride (KC1) at 10 (K1) and 150 mg (K2)/kg soil at the beginning of water deficit. Nodulation was examined and some nodule activities were assayed. Nodulation, nitrogenase activity, total nitrogen (N), and dry matter yield were significantly decreased by increasing stress but were significantly higher with the two levels of potassium (K) supply. Leghaemoglobin and protein contents of cytosol as well as nodule protease and invertase were severely depressed by drought stress. Soluble carbohydrate contents of nodules, however, was significantly increased. Protein and leghaemoglobin contents and enzyme activities were greater with K fertilization but less soluble carbohydrate was accumulated. The results indicate that K supply, particularly at the 150 mg/kg soil level, increased faba bean resistance to water stress.

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Abstract: Three-week-old nodulated faba bean plants were subjected to different levels of drought stress (onehalf, one-quarter, or one-eighth field capacity) for 5 weeks. Half the stressed plants were treated with KCl at 10 mg kg-1 soil or 150 mg kg-1 soil at the beginning of the drought stress. Nodulation and nitrogenase activity were significantly decreased by increasing drought stress. Leghaemoglobin and protein contents of nodule cytosol were also severely inhibited by drought sttess. This decline was attributed to the induction of protease activity. However, carbohydrate contents of the nodule cytosol increased significantly. This accumulation was attributed to a sharp decline in invertase activity and low use of sugar by the bacteroids We conclude that harmful effects of water deficits can be alleviated by increasing K+ supplementation.

Abstract: The effects of nitrogen applied at increasing levels of 0, 4, 8, 16 and 32 mM N (KNO3 or NH4Cl) were studied in faba bean (Vicia faba) nodulated byRhizobium leguminosarum bv.viceae RCR lool. Nitrogenase activity was higher at 4 and 8 mM N than the zero N treatment (control), but 16 and 32 mM N significantly reduced the efficiency of nodule functions. Nitrate reductase activities (NRA) of leaves, stems, roots, nodules and nodule fractions (bacteroid and cytosol) were increased with rising the NO3 − or NH4 + levels. NRA decreased in the order of nodules>leaves>stems>roots. Cytosolic NR was markedly higher than that recorded in the bacteroid fractions. Nitrate levels were linearly correlated to NRA of nodules. Accumulation of NO2 − within nodules suggests that NO2 − inhibits nodule’s activity after feeding plants with NO3 − or NH4 +.

Abstract: Two strains (RCR 1001 and 1044) and a commercial inoculant (Okadin) ofRhizobium leguminosarum biovarviceae were tested for their ability to survive in autoclaved clay soil for up to four months under heat, salinity and drought stress. Resistance to heat was tested by incubating rhizobia in soil at 27, 37 and 42 °C. Tolerance of rhizobia to salinity was investigated by growing rhizobia in soil salinized with 1 and 2 % NaCl (m/m). Drought resistance was tested by subjecting bacteria to soil moisture contents of 20, 10 and 5%. Strain RCR 1001 was more resistant to heat and nodulated faba bean better than other tested strains. A commercial inoculant Okadin survived more (plate count method) and nodulated faba bean (plant infectivity, most probable number, MPN) at moisture content of 5% and 2% NaCl. Although, strains RCR 1001 and 1044 resisted these stress conditions (plate count) they lost their abilities to nodulate faba bean (MPN-test). There is a possibility for selection of effective rhizobia which are more tolerant to harsh conditions.

Abstract: The effects of nitrogen applied at increasing levels of 0, 4, 8, 16 and 32 mM N (KNO 3 or NHaCI ) were studied in faba bean (Vicia faba) nodulated by Rhizobium leguminosarum bv. viceae RCR 1ool. Nitrogenase activity was higher at 4 and 8 mM N than the zero N treatment (control), but 16 and 32 mM N significantly reduced the efficiency of nodule functions. Nitrate reductase activities (NRA) of leaves, stems, roots, nodules and nodule fractions (bacteroid and cytosol) were increased with rising the NO 3" or NH4 + levels. NRA decreased in the order of nodules > leaves > stems > roots. Cytosolic NR was markedly higher than that recorded in the bacteroid fractions. Nitrate levels were linearly correlated to NRA of nodules. Accumulation of NO 2" within nodules suggests that NO 2 inhibits nodule's activity after feeding plants with NO 3" or NH4 §

Abstract: Two strains (RCR 1001 and 1044) and a commercial inoculant (Okadin) of Rhizobium leguminosarum biovar viceae were tested for their ability to survive in autoclaved clay soil for up to four months under heat, salinity and drought stress. Resistance to heat was tested by incubating rhizobia in soil at 27, 37 and 42 ~ Tolerance of rhizobia to salinity was investigated by growing rhizobia in soil salinized with 1 and 2 % NaCI (m/m). Drought resistance was tested by subjecting bacteria to soil moisture contents of 20, 10 and 5 %. Strain RCR 1001 was more resistant to heat and nodulated faba bean better than other tested strains. A commercial inoculant Okadin survived more (plate count method) and nodulated faba bean (plant infectivity, most probable number, MPN) at moisture content of 5 % and 2 % NaCI. Although, strains RCR 1001 and 1044 resisted these stress conditions (plate count) they lost their abilities to nodulate faba bean (MPN-test). There is a possibility for selection of effective rhizobia which are more tolerant to harsh conditions.

Abstract: The effect of N fertilizers on nodulation, nitrogenase, nitrate reductase activities and growth of two cultivars of soybean, Clark and Crauford was evaluated in a field experiment. KNO3 or NH4Cl were applied 27 days after planting at 0,16, 32, 64 and 128 kg N/ha. Nodulation and growth of both cultivars significantly increased when N was applied at low levels whereas specific N2-ase activity (SNA) slightly and insignificantly increased. Cv Crauford showed a greater positive response than cv. Clark. Higher rates of KNO3 and NH4Cl (128 kg N/ha) significantly depressed nodulation and SNA but slightly decreased the plant dry matter. Cv. Crauford was more tolerant to N fertilizers than cv. Clark. The decline in SNA was ascribed to increased nitrate reductase activity (NRA) and higher accumulation of nitrites in nodule cytosol. NRA and nitrate contents in nodules of cv. Clark were greater than that in cv. Crauford. Results showed that NH4 + is the preferred N source with occasional increases in nodule number and weight. This study provides an evidence for the nodulation and growth variability of soybean cultivars fertilized with different levels of N. The results also suggest that diminishing NRA could contribute to increased N2 fixation and the interaction between NO3 – assimilation and N2 fixation is strongly dependent on the plant cultivar.

Abstract: The effect of N fertilizers on nodulation, nitrogenase, nitrate reductase activities and growth of two cultivars of soybean, Clark and Crauford was evaluated in a field experiment. KNO3 or NH4Cl were applied 27 days after planting at 0,16, 32, 64 and 128 kg N/ha. Nodulation and growth of both cultivars significantly increased when N was applied at low levels whereas specific N2-ase activity (SNA) slightly and insignificantly increased. Cv Crauford showed a greater positive response than cv. Clark. Higher rates of KNO3 and NH4Cl (128 kg N/ha) significantly depressed nodulation and SNA but slightly decreased the plant dry matter. Cv. Crauford was more tolerant to N fertilizers than cv. Clark. The decline in SNA was ascribed to increased nitrate reductase activity (NRA) and higher accumulation of nitrites in nodule cytosol. NRA and nitrate contents in nodules of cv. Clark were greater than that in cv. Crauford. Results showed that NH4 + is the preferred N source with occasional increases in nodule number and weight. This study provides an evidence for the nodulation and growth variability of soybean cultivars fertilized with different levels of N. The results also suggest that diminishing NRA could contribute to increased N2 fixation and the interaction between NO3 – assimilation and N2 fixation is strongly dependent on the plant cultivar.

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Abstract: Azotobacter chroococcum was isolated from straw-amended soil and found to utilize 4-hydroxybenzoic acid, resorcinol, pyrocatechol and vanillic acid as sole carbon source. Growth and nitrogenase activity ofA. chroococcum were supported by 8, 6 and 4 mmol/L of 4-hydroxybenzoic acid, resorcinol and pyrocatechol, respectively. The generation time of 1.71 h in 4-hydroxybenzoic acid did not significantly differ from the generation time of 1.64 h, observed when grown in mannitol. 4-Hydroxybenzoic acid was utilized rapidly. However, the decomposition of other tested phenolic compounds set in only slowly. It was concluded that this isolate has good potential to utilize some phenolic compounds released during biodegradation of plant wastes.

Abstract: The ability of different microorganisms to alleviate the noxious effect of salinity was tested. Barley grains were planted under salt stress and were inoculated with cyanobacteria, Pseudomonas fluorescens and Dunaliella tertiolecta. All tested microorganisms improved growth of barley plants as indicated by dry weight, photosynthetic pigments and vitality of the plants. Cyanobacterial inoculant was the most effective and significantly diminished the adverse effect of salinity. Results of the present study hold promise for use of such microorganisms to cultivate plants in saline soils.

Abstract: The ability ofRhizobium andBradyrhizobium strains to solubilize phosphate from hydroxyapatite was determined in a medium containing NH4Cl or KNO3. The presence of NH4 + in the medium resulted in higher solubilization of phosphate as compared to the presence of KNO3, with the exception ofR. leguminosarium bv. viceae strain TAL 1236 and 1402 which solubilized comparable amounts of phosphate in a medium containing either KNO3 or NH4Cl. These results suggest that the strains employ two different mechanisms for phosphate solubilization, one depending on the presence of NH4 +, the other not requiring its presence. Temperature and aeration (O2 demand) optima were 30°C and 4.2 Hz (shaking frequency), respectively. In nonsterile soil the tested strain (R. meliloti TAL 1236) was very effective in solubilizing rock phosphate.

Abstract: Of 13 Rhizobium and Bradyrhizobium strains investigated for the production of cellular and extracellular phosphodiesterase and phosphotriesterase, all were found to produce both enzymes. Phosphodiesterase was produced at a much higher level than phosphotriesterase. Rhizobium meliloti TAL 1373 was the most productive. The extracellular enzymes were activated by inclusion in the assay mixture of Ca2+ or Mg2+. The enzymes were inhibited by Zn2+ but not significantly affected by Cu2+, Co2+ and Mn2+. Both hydrolases were inhibited by dithiothreitol but not by thiol-directed inhibitors, suggesting that sulphydryl groups are not directly involved in catalysis. The enzymes have the ability to hydrolyse some organophosphorus compounds, suggesting that Rhizobium and Bradyrhizobium strains play an important role in the degradation of organophosphorus pesticides

Abstract: Survival and nitrogenase efficiency ofNostoc commune andN. austinii were evaluated monthly in four carrier materials (sugarcane bagasse, wheat straw, wheat bran and peat) at 10, 30 and 40 °C. Survival, as well as nitrogenase activity, of both species was much better in peat, followed by wheat bran, sugarcane bagasse than in wheat straw at 10 and 30 °C up to three months, the activity ofN. commune being better thanN. austinii. None of the materials tested was found to be superior to peat as carrier ofNostoc species but the results indicated that wheat bran and sugarcane bagasse can be used as inoculant carriers with relative success. Storage of inoculants in these carriers is feasible at 30 °C up to three months.

Abstract: Rhizobium leguminosarum biovar viceae strain TAL 1236 growing on different organic phosphorus compounds as sources of phosphate exhibited phosphatase activities. The strain was able to produce both acid and alkaline phosphatases. However, its ability to produce alkaline phosphatase was much higher. When cellular phosphate fell to 0.115% of cell protein, cellular and extracellular phosphatase activities were promoted. Mg2+, Co2+ and Ca2+ enhanced slightly the activity of alkaline phosphatase more than acid phosphatase. However, Mn2+ and Fe2+ activated acid phosphatase rather than alkaline phosphatase. It may be concluded that Rh. leguminosarum plays an important role in the release of phosphorus from its organic compounds through the action of phosphatases which can be slightly activated by a range of cations.

Abstract: Inoculation of different plant wastes with microorganisms resulted in a release of maximum reducing sugars (33%) from sugar-cane leaves when subjected toPenicillium oxalicum. Maximum protein was formed from sugar-cane bagasse inoculated withAspergillus fumigatus. Association of sugar-cane leaves withP. oxalicum showed the highest digestibility. The use of such microorganisms may help to provide additional and valuable proteins ultimately for human use

Abstract: The effect of four bacterial and six fungal species on nodulation and growth ofVicia faba cv. Giza 3 inoculated withRhizobium leguminosarum biovarviceae strain RCR 1001 were assessed in a pot experiment.Bacillus cereus, Pseudomonas fluorescens, Aspergillus niger andA. quadriliniatus either alive cells or sterile filtrate significantly promoted nodulation, growth and nitrogen accumulation. Heat-killed cells had no effect.

Abstract: Of 13 Rhizobium and Bradyrhizobium strains investigated for the production of cellular and extracellular phosphodiesterase and phosphotriesterase, all were found to produce both enzymes. Phosphodiesterase was produced at a much higher level than phosphotriesterase. Rhizobium meliloti TAL 1373 was the most productive. The extracellular enzymes were activated by inclusion in the assay mixture of Ca2+ or Mg2+. The enzymes were inhibited by Zn2+ but not significantly affected by Cu2+, Co2+ and Mn2+. Both hydrolases were inhibited by dithiothreitol but not by thiol-directed inhibitors, suggesting that sulphydryl groups are not directly involved in catalysis. The enzymes have the ability to hydrolyse some organophosphorus compounds, suggesting that Rhizobium and Bradyrhizobium strains play an important role in the degradation of organophosphorus pesticides.

Abstract: Seeds of faba bean (Vicia faba L.) cultivar Giza 3 were screened for the presence of mycotoxins. Eleven out of 100 samples were positive. Aflatoxins B1 and B2 were found in 7 samples with a mean concentration of 30 μg kg−1 seeds. Aflatoxins B1 B2, G1 and G2 and ochratoxin A were each detected twice in separate samples with a mean concentration of 25 and 20 μg kg−1, respectively. Mycotoxins at concentrations of 100 or 200 μg kg−1 soil significantly decreased nodule number, nodule fresh weight and total nitrogenase activity. This was translated into reductions in dry matter accumulation and nitrogen yield of the bean. Mycotoxins also suppressed specific nitrogenase activity, NADH-dependent glutamate dehydrogenase (NADH-GDH) as well as glutamate synthase (NADH-GOGAT) activities. In addition, mycotoxins inhibited synthesis of leghaemoglobin, carbohydrate and protein in the nodule cytosol. Of the mycotoxins tested, aflatoxin B1 was the most toxic. The decline in nitorgenase activity and total N concentration in the plants could be attributed to mycotoxins interfering with normal nodule physiology and function.

Abstract: In soil salinized with different concentrations of sodium chloride, the total counts of soil fungi were significantly decreased during 11 weeks of incubation. Similarly, the total count of bacteria and actinomycetes were severely depressed by increasing salinity level above 5%. Invertase and urease activities were severely decreased as NaCl concentration increase during the incubation. Also, the effect on nitrate reductase was inhibitory with most treatments.

Abstract: The organophosphorus insecticide Selecron [O-(4-bromo-2-chlorophenyl) O-ethyl S-n-propyl-phosphorotioate] at 10 and 50 ppm significantly decreased respiration, mycelial protein, extracellular protein and mycelial dry weight of Aspergillus fumigatus, A. terreus and Myceliophthora thermophila when grown at 45°C. Cx and C1 cellulases of tested fungi were significantly decreased. However, C1 cellulase of A. fumigatus was slightly increased.

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Abstract: Survival of five genera of N-fixing cyanobacteria were studied under salt and drought stress 2 in clay and sand soil. These conditions considerably decreased the survival of the tested organisms. Nitrogenase activity was also decreased and this could be attributed to the reduced of heterocyst frequency under the exper- imental conditions. Apparently, Nostoc microscopicum and Rivulara natans appeared to be water stress-toler- ant species and remained for long period. There is a scope for selection of cyanobacterial species more tolerant to harsh conditions to prepare commercial inoculants for Agronomic practice.

Abstract: Six strains and a commercial inoculant ofBradyrhizobium japonicum were evaluated in association withGlycine max (L.) cultivar Clark. Inoculated and uninoculated plants were grown in pot and field experiments. Nodules were counted and weighed and roots and shoots were separated and analysed for total nitrogen. In pot experiments, two of six bacterial strains were superior to the other four, and to the commercial inoculant (Nitragin) in promoting greater root and top growth and plant nitrogen accumulation. In the field experiment, there were indications that environmental conditions may have affected nodulation by the bacteria. The strains could be divided into three groups according to nodule efficiencies, accumulation of plant dry matter, and total nitrogen content. The greater variations in nodule efficiencies of the tested strains could be attributed to the quantities of bacteroid, cytosol protein and leghaemoglobin in the nodules.

Abstract: Faba bean cultivar Giza 3 inoculated with Rhizobium leguminosarum RCR 1001 was grown in a pot experiment and irrigated with saline water (mixture of NaCl and CaCl sub(2) 0.25 Ca:Na on molar basis). Salinity levels of 5.8, 8.8, 11.6 and 14.6 dSm super(-1) (equivalent to 50, 75, 100 and 125 mM NaCl) significantly decreased nodule number, nodule fresh weight and total nitrogenase activity. Salinity inhibited specific nitrogenase activity, protein, leghaemoglobin and carbohydrate content of the nodules at 11.6 and 14.6 dSm super(-1) (100 and 125 mM NaCl). Salinity levels of 8.8, 11.6 and 14.6 dSm super(-1) (75, 100 and 125 mM NaCl) caused a significant reduction in dry weights of roots, stems, leaves and total plant nitrogen

Abstract: Pesticides (Brominal, Cuprosan and Fenvalerate) at 10 and 50 ppm suppressed growth, respiration and nitrogenase activity ofAzotobacter chroococcum, Azospirillum brasilense andAzospirillum lipoferum. The inhibitory effect on respiration ofAsm. lipoferum was most pronounced after 3 and 4 days

Abstract: Azotobacter chroococcum was grown on cultures containing five carbon sources alone and also in co-cultures with three cellulolytic fungi (Aspergillus niger, Penicillium funiculosum andTrichoderma harzianum). In the absence of fungal species, nitrogenase activity was relatively low. The best nitrogenase activity was recorded in cultures containing faba bean straw followed by that in cultures having wheat straw, sugar cane leaves, carboxymethyl cellulose (CMC) or cellulose. In co-cultures with fungi,Azotobacter showed substantial nitrogenase activity on all tested substrates.Azotobacter —Trichoderma association showed the highest nitrogenase activity.

Abstract: Potential nitrogen-fixing freshwater photosynthetic bacteria of 32 isolates from the Aswan High Dam Lake were investigated using the acetylene reduction technique to ascertain the magnitude of their contribution of fixed nitrogen to the ecosystem. The superior nitrogen-fixing Rhodospirillaceae were Rhodocyclus gelatinosus and Rhodomicrobium vannielii followed by Rhodobacter capsulatus, Rhodopseudomonas viridis and Rhodopseudomonas palustris. High and moderate nitrogenase activities (534 to 1528 nmol ethylene produced/4 ml/h) were found in 56% of the isolates, while the remainder showed low activities (76 to 477 nmol ethylene produced/4 ml/h).

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