جستجوی مقالات مرتبط با کلیدواژه « siderophore » در نشریات گروه « آب و خاک »

To date, no research has been done on the role of periphyton in paddy fields, especially on phosphate solubilizing ability of bacteria and fungi isolated from the biofilm. The aim of this study was to investigate the phosphate solubilizing ability and some other plant growth promoting (PGP) traits of bacteria and fungi isolated from the periphyton sampled from 20 paddy fields in Guilan province. In this study, 44 bacterial isolates and 32 fungal isolates capable of solubilizing phosphate were isolated. Among the microbial isolates, effective 10 bacterial isolates and 5 fungal isolates were selected for additional tests. The results showed that bacterial isolates 13B25 and 6B11, with the highest phosphate solubilization, solubilized 354 and 327.3 mg P l-1, respectively. The ability to produce siderophore (based on HD / CD index) by isolate 13B25 and 6B11 was equal to 3.2 and 3.4, respectively, with a significant increase (p < 0.001) compared to other isolates. The production of indole-3-acetic acid by the isolates 13B25 and 6B11 was 175.3 and 205.7 μg ml-1, respectively. Among the fungal isolates, two isolates, 6F11 and 8F12, were the best in PGP traits. The solubilization content of phosphorus by these two fungal isolates was 742 and 818 mg l-1, respectively. The results of molecular identification of effective bacterial isolates showed that 13B25 and 6B11 were most similar to Bacillus cereus and Acinetobacter calcoaceticus, respectively. In addition, fungal isolates 6F9 and 8F12 were most similar to Talaromyces minioluteu and Talaromyces stipitatus, respectively.

Azospirillum bacteria are one of the most important plant growth promoting rhizobacteria which exist in the rhizosphere of many crop plants. In this research, some soil and plant roots were collected from wheat and maize rhizosphere of the fields in Isfahan and were cultured in the tubes containing Nitrogen Free Bromothymol (NFB) medium. In order to isolate Azospirillum strains, the grown bacteria pellicles were streaked on NFB and Rojo Congo (RC) specific and semi-specific media. The bacteria were isolated and purified using morphological characteristics on the medium. After gram staining, catalase, oxidase and oxidative-fermentative tests, the detection and identification of Azospirillum isolates was done by molecular tests using PCR test with Az16S-A and Azo494-F/Azo756-R specific primers and 16S rRNA gene sequencing. Plant growth promoting characteristics (PGP) of Azospirillum isolates were determined by investigating the presence of NifH and NifD genes of nitrogenase enzyme by PolF/PolR and FdB260/FdB261 specific primers respectively. The properties of phosphate solubilization and production of chitinase, HCN, siderophores and indole acetic acid of isolates were performed by using specific tests. The replication of 646, 263, 360, and 390 bp fragments by Az16S-A, Azo494-F/Azo756-R, PolF/PolR and FdB260/FdB261 primers respectively, confirmed the presence of Azospirilum bacteria and the presence of NifH and NifD genes. Specific tests also revealed the ability of indole acetic acid production, insoluble phosphate solubilizationwith average value of 15 and 18.8 mg/l respectively and siderophore production in isolates. The results showed that some of the isolates possessed several PGP properties, while some of them had one or no characteristic. Finally, the sequencing of the 16S rRNA gene in some isolates determined and three species of A. brasilense, A. lipoferum and A. zeae identified in rhizosphere of wheat and maize plants.

Pseudomonas bacteria are the most important plant growth promoting rhizobacteria due to their widespread distribution in soil, their potential to colonizemany plant roots and possessing different plant growth promoting characteristics. The present study aimed to identify isolates of Pseudomonas fluorescens strains of olive tree rhizosphere in saline gardens of Qazvin province.  Plant growth promoting characteristics of  fifteen isolates of Pseudomonas fluorescens strains such as siderophore, auxin, hydrogen cyanide, ACC deaminase enzyme production, phosphorus solubility in liquid medium, pH changes and salt tolerance (NaCl, MgCl2 and CaCl2) (100, 200, 400 mM) were evaluated . Results showed that the dominant strains in producing ACC deaminase were Q7 and Q9, respectively. The Q2 strain was the best one to enhance the production of auxin (11.96 µg.ml-1). The solubility of phosphorus in conjunction with pH showed a negative correlation and the highest amount of dissolved phosphorus was related to Q13 (251) isolate. Also, the half of strains (40%) was not able to produce HCN. Commonly, all studied strains were able to produce siderophore after two, four and six days of incubation. Expect Q1 and Q8, other strains were able to grow in the considered salt concentrations. Based on the results, we concluded that some of these strains can be targeted for genomics studies to improve salt stress resistance in plants and orchards under saline soils conditions.

Endophytic fungi increase plant growth and confer stress resistance to plants  with different mechanisms. In order to identify endophytic fungiof Pistacia vera and to evaluate their growth promoting and biocontrol properties, samples were taken fromthe leaves and fruits of Pistacia vera in Rafsanjan. After morphological and molecular identification, Growth stimulating factors were evaluated by estimating auxin production, siderophore production and inorganic phosphate solubilizing activity. Biocontrol activities were evaluated based on chitinase and hydrogen cyanide production. Mean comparison of the data showed that the highest amounts of auxin at levels of 0 and 50 mg/L of tryptophan were produced with Trichoderma atroviride TA2-2-1as the amount of 19.34 and 32.88 mg/L, respectively. Quambalaria cyanescens QC11-3-2 produced the highest amount of siderophore which the ratio of the diameter of the halo zone to the colony was 2.96. Only, Byssochlamys nivea BN1-1-1had the ability to solubilize the inorganic phosphate which the ratio of the halo zone diameter to the colony diameter was 1/1. Most chitinase activities were observed by Trichoderma harzianum TH 5-1-2 (2.92 U/mL) and T. atroviride TA2-2-1 (2.34 U/mL), respectively. T. atroviride TA2-2-1 and Clonostachys rosea CR2-3-1 were able to produce the HCN.

Wheat is one of the most important food crops. In modern agriculture, due to the increase in human population and the detrimental effects of pesticides such as environmental pollution, concerns about human and animal health, adapting suitable alternatives which have none of these dangerous effects would be necessary. This is possible by increasing the production of bio-fertilizers. Plant growth-promoting rhizobacteria (PGPR) are the beneficial rhizosphere bacteria that can enhance plant growth directly or indirectly through a wide variety of mechanisms. PGPR can stimulate plant growth directly by supplying nutrients such as phosphorous and nitrogen or by the production of phytohormones such as auxins, cytokinins (CK), gibberellins (GAs) or ACC deaminase synthesis. They can also promote plant development indirectly by the suppression of pathogens by different mechanisms such as biosynthesis of antimicrobial molecules or antibiosis induced systemic resistance (ISR), rhizosphere competition, cell wall degrading enzymes like chitinase and HCN production. In this study, amplified ribosomal DNA restriction analysis was performed for screening the bacterial isolates. Then phosphate solubilization, siderophore and auxin release activities and effect of bacterial isolates on wheat seed germination traits were studied.
In order to isolate wheat rhizosphere bacteria, soil samples were taken from the wheat rhizosphere of Tehran, Qazvin, Zanjan, West and East Azerbaijan, Kurdistan and Hamadan provinces. Genomic DNA of each isolate was extracted by using a modified cetyl trimethylammonium bromide (CTAB) method. Amplified ribosomal DNA restriction analysis with HpaII and RsaI restriction enzymes was done for genetic screening. Growth stimulating factors were evaluated by auxin production, siderophore production, and inorganic phosphate solubilizing activity. Siderophore production was determined by measuring the diameters of the colony (mm) and of any orange halo (mm) formed from the blue medium surrounding bacterial growth on CAS Blue Agar medium. To examine Pi solubilization capability, 2µ bacteria suspension was placed on the plates containing Sperber’s medium. Cultures were incubated at 25 ± 2 °, when the diameters of the colony and of the halo zone surrounding it were measured and the mean ± SE of the ratios of halo (mm)/colony (mm) calculated. In order to evaluate the production of auxin, isolates were grown in 100ml flasks containing 25ml TSB medium for 48h on a rotary shaker. 1 ml supernatant was mixed with 2ml of Salkowsky reagent after centrifugation at 10000g for 15min. The absorbance of the complex was read at 535nm in a Spectrophotometer. To investigate the effect of bacterial isolates on germination traits, radicle and plumule fresh and dry weight, radicle and plumule length, germination percentage, germination rate, and germination average rate were measured. The data were analyzed with using SAS 9.1. Mean comparisons were performed by LSD and main effective interaction was found significant at P 20 isolates of wheat rhizosphere bacteria were subjected to amplified ribosomal DNA restriction analysis. The 16S rDNA region was amplified by polymerase chain reaction and PCR products were digested by HpaII and RsaI restriction enzymes. From each pattern, one sample was sent to sequencing. Different species including; Chryseobacterium ginsenosidimutans, C. lathyri, C. piperi, C. taiwanense, Novosphingobium aromaticivorans, Pedobacter duraquae, and Sphingomonas koreensis were identified from the wheat rhizosphere. Bacteria were tested for their plant growth promoting qualities. All of the strains produced auxin from 1.90 to 25.93. Mean comparison of the data showed that the highest level of auxin was produced with F1 and the lowest amount was observed by F18. Phosphate solubilization measured as a halo zone on Sperber’s medium was observed with F6 and F56 isolates. The ratio of the diameter of the halo zone to the colony diameter was 2.86 with F6. The highest level of siderophore production by wheat rhizosphere bacteria, observed as halo formation around colonies on CAS Blue Agar medium, was obtained with F46, followed by F45 and F3. The ratio of the diameter of the orange halo surrounding bacterial growth to the colony diameter was 2.86 with F46. The result showed that the effect of wheat rhizosphere bacteria on germination traits such as radicle fresh and dry weight, plumule fresh weight, radicle and plumule length, germination percentage, germination rate, and germination average rate was significant at the one percent level and the effect of wheat rhizosphere bacteria on plumule fresh weight was significant at the five percent level.
Plant growth promoting bacteria enhance the growth and development of plants with different ways. These bacteria affect the growth and development of crops by phosphate solubilization, production of hydrogen cyanide, siderophore, and hormones such as auxin, gibberellic acid and cytokinins. According to the result, due to growth promoting characteristics such as siderophore and auxin production, phosphate solubilization, and the improvement of the seed germination traits, it can be possible to prepare bacterial inoculant for the field experiment in order to increase the availability of nutrients and improve the growth of plants.

Plant inoculation with effective plant growth promoting and heavy metal resistant rhizobacteria is an efficient method to improve the phytoremediation efficiency and extraction of heavy metals from contaminated soils. With respect to this reason, astudy was conducted to isolate, identify and evaluate the growth stimulating traits of copper-resistant bacteria from a Cu-contaminated soil. Six rhizospheric soil samples of indigenous plants were collected in Sarcheshmeh Khatoonabad, Kerman province. After screening, six strains were selected. Phenotypic, biochemical and genetic identification data showed that five and one isolates were belong to Pseudomonas and Bacillus genera respectively. Then, the minimum inhibitory concentration of copper, siderophore production, auxin and hydrogen cyanide production, the ability to solubilize mineral phosphate in solid and liquid medium, the ability to solubilize Zn low soluble compounds in solid and liquid medium and production of ACC-deaminase were investigated. The results indicated that all of the isolates were resistant to various concentrations of copper. The maximum resistance to inhibitory concentration of copper was related to K4 and K5 strains at a concentration of 400 mg L-1 of copper. All of the strains were able to produce siderophore in CAS medium except for K6 strains and strain K5 was also the superior in siderophore production. Among the strains, K4 and K6 were not able to produce auxin. There was also a significant difference between auxin productions by isolates K1 with the other isolates, with the highest auxin production (2.07 mg L-1). The results also demonstrated that among the strains, only K4 strain was capable of producing hydrogen cyanide (degree: four=relatively high) and the other isolates were reported as non-production of hydrogen cyanide (degree: one). The results of Three Calcium Phosphate (TCP) solubilizing by isolates in PKV broth medium showed that K1, K2, and K3 strains had the most phosphorus solubility (706, 661 and 588 mg L-1) respectively and there wasn’t significant difference between them. The results demonstrated that K4 and K5 isolates with 0.910 and 0.850 halos to colony diameter had a significant difference with other isolates in solid medium containing ZnCO3 and the rest of the strains, K1, K2, K3 and K6 did not show the ability to solubilize the zinc carbonate as well. The solubilizing of solid zinc oxide in solid medium by K4 strain (halo:colony, 2.11) was the highest solubility of zinc oxide and K1, K2, K3 and K6 strains were not able to dissolve the zinc oxide in the solid medium. They did not show the ability to dissolve the low soluble zinc oxide nor the zinc carbonate compounds. K4 strain had the highest zinc carbonate solubility in the broth (12.5 mg L-1) and the highest solubility of zinc oxide in the broth was attributed to K4 strain (9.76 mg L-1). According to the results, these isolates can be used for enhancing phytoremediation efficiency of this element in contaminated soils.

Nitrogen fixation is a biological process, which provides atmospheric nitrogen in usable form for plants, and satisfies the plants N requirement and can replace chemical fertilizers in high proportion. On the other hand, calcareous and high pH soils have usually small amounts of nutrients in available forms and use of plant growth promoting rhizobacteria can increase the availability of nutrients. Soybean nodulating rhizobia and establishment of their symbiosis is affected by different factors in soil. The objective of this research was to isolate and screen the root nodule rhizobia of soybean and evaluation of their resistance to some stresses and capability production of some growth promotion metabolites and biocontrol agents in selected bacteria.
Soybean root nodules have been collected from 21 different fields in various zones of Golestan province, Iran. Root nodules surface sterilization was performed by immersing intact nodules for 30 seconds in 95% alcohol and immediately transferred into 2.5% sodium hypochlorite for 2-3 minutes and finally were rinsed seven times by sterile distilled water. The sterilized nodules were crushed using 1 ml of sterile water in test tube and the slurry was streaked on Yeast Extract Mannitol Agar (YMA) containing Congo red. The inoculated petri plates were incubated at 28°C for 3-6 days. Plant nodulation test was done with 21 rhizobial isolates under sand condition in pot experiment. The different rhizobial isolates were screened for stresses tolerance (salinity, drought, temperature,), herbicide and antibiotics resistance, production of hydrolytic enzymes, siderophore and hydrogen cyanid (HCN).
Nodulation assay showed only 11 of 21 isolated strains formed nodule on soybean roots. Only three of the isolates produced siderophore and none of them showed HCN production capability. The results showed that all the strains tolerated up to 5% NaCl. Evaluation of tolerance to temperatures showed that only isolates No. 2 and 16 were sensitive to 42 °C and the other strains grew well at high temperature. All the isolates were sensitive to tetracycline antibiotic while no inhibitory effect of the chloramphenicol and streptomycin was observed on growth of rhizobial isolates. Between two herbicides Trifluralin showed more inhibitory effect on rhizobial growth than Gallant super. Drought stress imposed by polyethylene glycol affect negatively the rhizobial growth and the severity effect depends on rhzobial isolates and drought levels. Capability of hydrolytic enzymes secretion showed that 14.2, 42.8 and 47.6 % of the isolstes produced α-amlyase, cellulose and protease, respectively.
Plant growth promotion characteristics of bacterial isolates, in this research, showed that some of the isolates had the potential to use as PGPB. Those isolates capable to produce siderophore and protease, amylase and cellulase secretion as well as have the ability to grow under various stresses conditions, could use as potential isolates in inoculum production to evaluate their nitrogen fixation in soybean –rhizobium symbiosis under pot and field culture.

Successful phytoremediation of metal-contaminated soils largely depends on their bioavailability in soil. Samples of a contaminated soil with elevated concentration of Zn were applied in the pots to evaluate the interactive effects of DFOB siderophore (0, 70 and 140 μM kg−1) and metal tolerant bacterial inoculation (p0, p15, p18, and p19) on Zn accumulation in corn and metal speciation and sequential fractions in soil. Results indicated that bacterial inoculation increased Zn concentrations in corn shoot. Addition of DFOB (140 μM kg−1) to pots of the soil which was inoculated with p15 isolate significantly enhanced Zn concentration in roots as compared to control. The uptake of Zn by shoots was increased in pots inoculated by bacterial isolates compared to those in the un-amended soils. Ligand addition significantly enhanced the concentration of DTPA-extractable Zn. Also co-application of DFOB and bacterial inoculation significantly decreased Zn bound to carbonates fraction and increased water soluble Zn concentration. Based on the results of this study, it can be concluded that co-application of DFOB and metal tolerant bacteria are efficient in increasing the bioavailability of Zn when expressed relative to the control treatment, which might be of great significance for the successful phyto-extraction of Zn-polluted soils.

In order to study the effect of Synorhizobium meliloti on growth and nutrients uptake of sesame, a greenhouse test was carried out. The first isolates investigated in IAA and siderophore producing and their ability in solubilizing inorganic phosphates. The results showed that all of isolates were able to produce auxin with different among. The maximum amount of IAA production was 59.5 g ml-1 that was related to SR24 isolate. All isolates could solubilize tricalcium phosphate (Ca3(PO4)2) in Sperber medium, and SR18 with 139 µg ml-1 had the highest ability to solubilize tricalcium phosphate. Also SR3 and SR32 isolates produced the highest amont of siderophore. According to the results, five isolates that were better in IAA and siderophore producing and solubilizing inorganic phosphates were selected and used in a greenhouse test. This experiment was conducted base on completely randomized design with five treatment including four isolates of Synorhizobium meliloti and one treatment without bacteria as control and four replications. The results indicated that inoculation of isolates enhanced Sesame shoot dry weight compared to control and this increasing was significant for SR18, SR16 and SR3. Application of most isolates also increased measured nutrients uptake in Sesame shoot. However only isolate SR18 significantly increased the nutrients uptake including P, Zn, Cu and Fe compared to control.

Quality control of biofertilizers has several aspects that attention to properties of plant growth promoting of bacteria which used in biofertilizers as part of their quality control is taken into consideration. In this study, four kinds of biofertilizer commonly used in the Iran, including Nitroxin, Supernitroplus, Biosuperphosphate (industrial biotechnology company mehre Asia) and Barvar2 (produced in Greenbiotech Company) were selected and examined. Isolates used in Biofertilizers Ba1 and Ba2 from Barvar2, Bio1, Bio2, Bio3 and Bio4 of Biosuper phosphate, SN1 and SN2 of Supernitroplus and N1, N2, N3, N4 and N5 of Nitroxin were evaluated for the solubilizing ability of organic and inorganic phosphates, auxin and siderophore production, and K release in both qualitative and quantitative methods. The results showed that the Ba1 strain with a maximum ratio of diameter of the clear zone to the colony (3.26 mm) and phosphate solubilizing (606.4 mg/l) in both qualitative and quantitative methods, had the maximum ability to dissolve insoluble inorganic phosphate compound Ca3(PO4)2 compared with other treatments. However, Ba2, another strain of Barvar2, with mineralizing ability of 62.23 mg/l had the greatest ability in phosphate mineralization. The isolates used in Nitroxin had good results for production of auxin and siderophore. So, maximum production of auxin and siderophore were observed in N4 (15.13 mg/l) and N3, respectively. Isolate N3 produced largest orange zone in qualitative assay and 124.54 µm siderophore in quantitative methods, respectively. The isolates, Ba1 and Bio1 had highest ability to release potassium from the Muscovite and Biotite respectively compared with other treatments. In view of the PGPR features, Biofertilizers Barvar2 and Nitroxin had a better situation. Biofertilizer Biosuperphosphate was in the next order but isolates used in Supernitroplus had the weakness results.

This study was performed in order to isolate lead (Pb)-tolerant plant growth promoting rhizobacteria in Pbcontaminated soils and to evaluate their potential for production of plant promoting substances. The isolated Pbtolerant rhizobacteria were identified as Rhodococcus sp., Bacillus stearothermophilus strain A, Corynebacterium sp., Bacillus pumilus, Mycobacterium sp., Bacillus stearothermophilus strain B, Bacillus licheniformis and Bacillus sp. The results showed that all isolates were able to tolerate high concentrations of Pb. The minimum inhibitory concentration (MIC) of these bacteria was in the range of 1100 1720 mg l-1 (3.3-5.19 mM). In addition, all isolates produced IAA (ranging from 3.53 to 43.64 mg l-1) and siderophore (ranging from 57.74 to 86.24%). However, only two isolates (i.e., Bacillus licheniformis and Mycobacterium sp.) had the ability to produce bacterial enzyme ACC-deaminase. Inoculation of medium containing poorly soluble PbCO3 with bacterial strain Corynebacterium sp. significantly increased the available concentration of Pb.

The phosphate solubilization capability of actinomycetes has recently attracted interest but the mechanism and medium composition effect involved in this process was not clarified. Seven actinomycete isolates were characterized and their phosphate solubilizing activity, phytate degradation, siderophores, indole acetic acid (IAA) and hydrogen cyanide (HCN) production were investigated. Additionally, all isolates were evaluated as plant growth promoters to maize in pot experiment. Our results showed that the selected isolates were able to solubilize tri-calcium phosphate (TCP) only when synthetic minimum medium (SMM-agar) was supplemented with ammonium nitrate. Similarly, TCP solubilizing activity in liquid cultures was also observed (from 11 to 216 μgml-1) when medium was supplemented with ammonium nitrate and this behavior was strongly associated with a pH reduction. Phytate degradation (1.7-95%), indole acetic acid production (6.26 to 27.81 μg ml-1) and siderophore production (1.24 to 2.45 Halo to clony ratio) was observed in all strains, but no isolates produced HCN. Significant increase in maize shoot height, fresh weight, dry weight and P uptake (P<0.05) was observed in inoculated plants compared to uninoculated control. Streptomyces sp. 47 showed the best plant growth promotion performance while plants inoculated with Streptomyces sp. 50 showed a remarkably higher P uptake. Both strains were considered as suitable potential inoculants for increasing early maize growth and P uptake.

Azotobacter is an important bacteria in crop rhizosphere. This research aimed the isolation of local Azotobacter under cultivation of soybean plant in Golestan province and their potential growth promoting-ability. After identification of 30 isolates their ability to molecular nitrogen fixation were tested with Acetylene to Ethylene reduction method. Their ability in auxin production and solubilizing the mineral P were tested with colorimetric method and sidrephore production potential was tested with Cas-agar medium. The maximum nitrogen fixation was in Az26 (428.23 nm.vial.h-1 ethylene) and minimum in Az27 (21.39 nm.vial.h-1 ethylene). Auxin production was highest in Az4 isolate (27.3 mg/l) and lowest in Az20 isolate (0.0157 mg/l). Also maximum sidrephore production was in Az9 and minimum in Az18 observed with diameter halo on colony of 6.36 and 2.24 in 72 hours respectively.

In this study, 14 strains of A. chroococcum isolated from wheat grown fields around the city of Tabriz, in northwest of Iran, were assayed for siderophore production using chrome azurol-S agar (CAS-agar) method under in-vitro conditions. Results showed that some strains had relatively higher ability in siderophore production. In a pot culture experiment with sterile soil, wheat plants (Triticum aestivum L.CV. Falat) were inoculated with 14 bacterial strains. Positive control received nitrogen fertilizer without bacterial inoculation and negative control was left un-inoculated and without N- fertilizer. Totally, 16 treatments with four replications were arranged in completely randomized design. Concentartions and contents of Fe, Cu, Zn and Mn in shoot and root as well as translocations of these elements from root to the shoot were determined at the harvest time. Results showed that the inoculation with Azotobacter had significant effects on concentrations and contents of Fe, Zn and Cu in shoot and root. Translocations of Fe, Zn and Cu from root to the shoot were markedly increased in bacterial treatments compared to the positive and negative controls. Mn concentration and content as well as its translocation from root to the shoot were not significantly affected. In-vitro assessment of siderophore production revealed that the higher siderophore production in bacterial stains was in accordance with higher Fe in plant tissue and its translocation as well.

Azotobacter chroococcum is an important PGPR (Plant Growth Promoting Rhizobacteria) producing compounds needed for plant growth. The aim of this research was to study the effects of different native strains of Azotobacter chroococcum on growth and yield of wheat under greenhouse counditions. Seeds of spring wheat (Triticum aestivum L. var. Pishtaz) were inoculated with some Azotobacter chroococcum strains capable of producing IAA, HCN, sidrophore and fixing molecular nitrogen. The inoculation of wheat with those strains had a positive, significant effect on biological yield, seed protein percentage, thousand seed weight, leaf area, N, P, Fe and Zn uptake, in particular, by wheat. The increased growth of wheat was most likely due to the production of IAA and enhanced nitrogen fixation by inoculated strains. Some strains of Azotobacter chroococcum native to Chaharmahal va Bakhtiari are established as PGPR. Results also support the efficiency of Azotobacter chroococcum as an important biofertilizer in wheat cropping systems. The selected strains had a significant effect on wheat growth and yield, including biological yield and seed quality under greenhouse counditions. This beneficial effect of Azotobacter chroococcum on wheat is attributed mainly to IAA production and, to some extent to non symbiotic nitrogen fixation in the rhizosphere. So, these strains can potentially be used to improve wheat nutrition of micronutrients such as Fe and Zn, in particular.