ISSN: 0973-7510

E-ISSN: 2581-690X

B. Deb Roy1 , B. Deb1 and G.D. Sharma2
1Microbiology Laboratory, Department of Botany, Gurucharan College, Silchar – 788 004, India.
2Microbiology Laboratory, Department of Life Science, Assam University, Silchar – 788 011, India.
J Pure Appl Microbiol. 2009;3(1):117-124
© The Author(s). 2009
Received: 27/11/2008 | Accepted: 08/01/2009| Published: 30/04/2009
Abstract

Six species viz., Azotobacter chroococcum, Azospirillum amazonense, Beijerinckia indica, Derxia gummosa, Bacillus polymyxa and Pseudomonas fluorescence of diazotrophs were isolated from the acid stress rice agro-ecosystem soils of South Assam (Barak Valley). Azotobacter chroococcum and Azospirillum amazonense have showed a wide range of distribution in the rice fields with higher number of viable cells. The viable cell count of Azotobacter chroococcum, Azospirillum amazonense and Bacillus polymyxa strains was more in autumn or sali cropping season (August-December) than in summer or ahu cropping season (May-August). Beijerinckia indica, Derxia gummosa and Pseudomonas fluorescence strains have shown higher number in summer (ahu) season. The population of diazotrophs fluctuates with the pH of rice agro-ecosystem soil. The population of Azotobacter chroococcum, Azospirillum amazonense and Bacillus polymyxa was high at higher soil pH whereas the population of Beijerinckia indica, Derxia gummosa and Pseudomonas fluorescence was more at lower soil pH. Beijerinckia indica and Derxia gummosa strains were more acid tolerant than the other isolated strains. The N2-fixing potential of Azotobacter chroococcum was highest among the isolated diazotrophs. Overall, Azotobacter chroococcum, Azospirillum amazonense and Beijerinckia indica strains were found to predominate in the rice agro-ecosystem soils of South Assam (Barak Valley).

Keywords

Acid stress, Diazotrophs, Diversity, Rice agro-ecosystem, South Assam

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