Abstract
In this study, thirty-six local isolates of rhizobial bacteria were isolated from root nodes of different leguminous plants collected from different areas in Nineveh Governorate/Iraq. The rhizobial colonies were purified and their agronomic and biochemical characteristics were studied. Results of this study showed that the local isolates had the ability to consume different sugars as a carbon source. Also, the antibiotic sensitivity test showed that only one isolate, Rhizobium leguminosarum bv. phaseoli AS12 was resistant to the antibiotic Azithromycin 15 µg/ml, and the isolate Rhizobium leguminosarum bv. phaseoli AS14 showed resistance to the antibiotic Gentamycin 10 µg/ml, and the rest of the isolates showed different rates of resistance and sensitivity for the rest of the antibiotics. The local isolates showed different NaCl tolerance levels up to 8.0 %, while no tolerance was observed for Rhizobium leguminosarum bv. viciae AS11 isolate at any of the studied concentrations. Results of heavy metal salt tolerance study showed that the isolates of Ensifer meliloti AS34 and Rhizobium leguminosarum bv. viciae AS36 were sensitive to ZnSo4 at a concentration of 25 µg/ml, while the tolerability of the other isolates to the studied heavy salts differed at concentrations higher than 25 µg /ml. All the studied isolates showed a positive result in staining with Congo red and Aniline blue dyes. Maximum exopolysaccharide production was 494 mg/Li by Rhizobium leguminosarum bv. viciae AS35. Antimicrobial activity test showed maximum inhibition zone 17 mm by Rhizobium leguminosarum bv. viciae AS36 against Proteus vulgaris.
Highlights
Gaseous nitrogen (N2) is abundantly available in the atmosphere
Research Method Isolation of rhizobial bacteria from the root nodules of leguminous plants: Host leguminous plants were uprooted with an amount of soil and washed
After that the root nodules were destroyed under sterile conditions with sterile rod glass in 1 ml of physiological solution. 0.1 ml of different dilutions of bacterial suspensions were spread with glass diffuser on Tryptone Yeast Extract (TY) agar plates to obtain single pure colonies
Summary
Gaseous nitrogen (N2) is abundantly available in the atmosphere. Plants and animals cannot convert it into a biological useful form. These organisms reduce the gaseous dinitrogen (N2) to ammonia This process, known as biological nitrogen fixation, is carried out by the enzyme system nitrogenase. Other organisms fix nitrogen only in symbiotic relationship with a eukaryotic host plant, like rhizobia in legume symbiosis, Frankia in actinorhizal symbiosis and Cyanobacteria in Gunnera symbiosis [1]. The establishment of symbiotic association takes place in several steps like recognition and infection of root hairs, development and differentiation of root nodules, multiplication of rhizobia and their converts into bacteroids within plant cells and conversion of nitrogen to ammonia. Tryptone Yeast Extract (TY) Swarm Plate Medium: This medium was prepared by adding 3 gm/Li agar to the TY medium
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