Isolation and selection of nitrogen fixing endophytic bacteria in rice

Rice (Oryza sativa) is an economic crop of Thailand. Nitrogen is an important nutrient for growth and yield of rice. Chemical fertilizers have been used in rice cultivation, which increase cost. Naturally, some endophytic bacteria can fix N2 from the air and convert to nitrogen compounds that are useful to plants. In this study, endophytic bacteria were isolated from five rice varieties (Muey Nong 24, Muey Nong 25, Pathum Thani 1, Suphan Buri 1 and Chai Nat 1). One hundred and twenty- three of endophytic bacteria were isolated from the roots, stems and leaves on Nitrogen free agar. Nitrogenase activities of the endophytic bacteria were determined by Acetylene reduction assay. The endophytic bacteria with high nitrogenase activities in the range of 26-120 nmol C2H4/mg protein/hr were selected for identification. The selected bacterial isolates were found in the genera of Pseudomonas (CS5), Sulfidobacillus (25R14), Enterobacter (SS6), Enterobacter (CR9), Enterobacter (SS5), Bacillus (25R2) and Sulfidobacillus (SR1).