Nitrate and sulfate reducers-retrievable number of bacteria and their activities in Indian waters

Abstract

Culturable heterotrophic, nitrate reducing and sulfate reducing bacteria (HB, NRB and SRB) were enumerated from 25, 50, 100 and 200 m depths at 15 stations and their potential activities viz. Nitrate reducing (NRA) and Sulfate reducing (SRA) were determined. NRB and SRB were observed throughout these depths and did not relate to HB numbers. HB and NRB were recorded at 3 orders per ml and SRB at 2. High numbers of reducers were encountered in shallow depths as frequently as in deeper waters and did not correlate to potential activities. Average NRA showed decreasing trend with depth from 60 mu g at/ml/hr. at 25 m to 2.4 mu g at/ml/hr. at 100 m. However the activity was 2.6 times higher at 200 m when compared to that at 25 m. SRA showed a steady decreasing trend from 0.16 mu g at/ml/hr at 25 m to 0.03 mu g at/ml/hr at 200 m. It is suggested that while activities of SRB and shallow water NRB are dependant more on the carbon regime of their source, NRA of the deeper waters are more dependant on the nitrate regime