Identification of culturable anaerobic bacteria associated with paddy field soil and its influence on RSA modulations under in vitro condition

Culturable anaerobic bacterial populations on paddy field soil were found on the order of 102 CFU-1 g of soil-1, and the percentages of spores were usually less than 1% of the total anaerobes. Anaerobic bacteria were isolated from the soil samples by picking up colonies on the roll tube agar. The nitrogen fixing obligate and facultative anaerobes were isolated and characterised from paddy ecosystem. The phylogenetic analysis of 30 isolates based on 16S rRNA gene sequences revealed that the composition of dominant culturable anaerobic bacteria on rice soil was rather simple. Molecular analysis based on 16S rRNA gene sequencing revealed that the anaerobic N2 fixing bacterial isolates NFTh2 showed maximum similarity with Clostridium pasteurianum. Higher nitrogenase activity was noticed for the screened obligate and facultative anaerobic bacteria and exhibited maximum activity on 132th day (19.81 n moles of C2H4 mg-1 protein h-1. In the present investigation, the occurrences of anaerobic nitrogen fixer in the paddy ecosystem and their role in the RSA modulations as influenced by anaerobic nitrogen fixer under gnotobiotic condition have been examined.