ABSTRACT
Stenotrophomonas maltophilia was isolated from paddy field of Kyaukse District, Mandalay Division, Myanmar. Nitrogen fixing activity of S. maltophilia was detected in nitrogen free mineral medium supplemented with different carbon sources. S. maltophilia accumulated highest amounts of ammonia in glucose supplemented medium. But their nitrogen fixing activity was best at 0.7% glucose concentration. When 0.5609 ppm of glucose still remained in the medium after 24 hours incubation, no ammonia was detected. After incubation of 32 hours, ammonia began to accumulate and the amount of 0.5 ppm of ammonia was detected but no sugar remained in the medium. Highest amount of ammonia (2 ppm) was accumulated in the medium after 48 hour incubation. So we found that ammonium accumulation began when no sugar remained in the medium, supposing that sugar plays a key role in ammonia accumulation.