Isolation of free-living nitrogen-fixing bacteria from the rhizosphere of rice.

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Abstract
Bacterial flora of rhizosphere of the rice plant was examined to determine the relationship of nitrogen-fixing bacteria to rice plants. Of 7,344 bacterial strains from the rhizosphere. 1,005 strains (13.7%) reduced acetylene. Representative 74 strains with acetylene reduction activity were selected for identification. All of these strains were gram negative, aerobic or facultatively anaerobic, and most had ubiquinone (Q-10) and cellular fatty acid composition, mainly with straight-chain fatty acids. Twenty-two strains were assigned to the following known species: Azospirillum brasilense Tarrand, Krieg and Dobereiner (1 strain), Azospirillium lipoferum Tarrand, Krieg and Dobereiner (1 strain), Enterobacter cloacae (Jordon) Hormaeche and Edwards (4 strains), Erwinia herbicola (Lohnis) Dye (2 strains), Klebsiella oxytoca (Flugge) Lautrop (6 strains), and Xanthobacter autotrophicus (Baumgarten, Reh and Schlegel) Wiegel, Wilke, Baumgarten, Optiz and Schlegel (8 strains). Fifty-two strains could not be assigned to any known species.