Sulfate-Reducing and Sulfur-Oxidizing Bacterial Activity in the Coastal Waters of Arabian Sea During Post Upwelling Season

Abstract

The synergistic existence of sulfate-reducing bacteria (SRB) and colorless sulfur-oxidizing bacteria (CSOB) involved in nutrient turnover is sparsely documented in coastal waters. To understand the processes mediated by these physiological groups we proposed to analyze their abundance and activities and the extent of interaction with various environmental parameters. Therefore, water samples were collected during post upwelling phase off Calicut and Kochi in August 2008. Stations at 30 m, 50 m, 100 m water depths were considered as nearshore, and those at 300 m and 500 m were considered as offshore. Maximum sulfate-reducing activity (SRA) of 86 nM d−1 was in the nearshore surface waters of Kochi and 30 nM d−1 in offshore bottom waters of Calicut. In these waters, SRA was dictated by total suspended load and phaeophytin, respectively. Maximum number of CSOB of 1.76 × 106 cells l−1 was detected in the surface waters of both the stations. At both nearshore and offshore waters of Kochi and Calicut, CSOB related to the sulfur-oxidizing activity (SOA) which ranged from 3 to 577 µM d−1 and 3 to 223 µM d−1, respectively. This paper elucidates the coupling between SRB and CSOB and their contribution towards nutrient regeneration and restoration of homeostasis during the waning phase of upwelling in these coastal waters.