Abstract
Nodules obtained from the roots of fenugreek (Trigonella foenum graecum), a leguminous plant yielded three distinct classes of Nitrogen fixing bacteria. Molecular phylogeny based on 16S rRNA gene sequences showed them to be Enterobacter cloacae (R1), Pantoea dispersa (R10) and Enterobacter ludwigii (R12). The biochemical and morphological characterization of the three bacteria showed many similarities. All were gram negative, rod shaped, giving identical biochemical reactions like Catalase test, MR tests, oxidase test etc. However there were differences in their sensitivity to the abiotic stresses like salinity, tolerance to heavy metal ions and temperature. Sensitivity to antibiotics also showed similar responses. Co-infecting the same plant and occurrence in the same nodules by different genera of bacteria, capable of Nitrogen fixation is a novel phenomenon. The commonly held belief that all Nitrogen fixing mucoid bacteria occurring in nodules of legumes are Rhizobial species is not tenable. Plant growth promoting effects of these bacteria were observed by IAA, siderophore production and inhibition of ethylene biosynthesis by plants by producing the enzyme, ACC Deaminase. The host specificity for one of the bacterium, R1 was shown as only Fenugreek showed nodulation but not mung bean or Bengal Gram seedlings. Nitrogen fixation by the isolated bacteria showed all of these could reduce acetylene to ethylene by gas chromatography.
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