Bacterial Community Composition Markedly Altered by Coastal Hypoxia.

Monsoonal upwelling along south and central west coast of India leads to intense biological productivity. As a consequence of excess organic matter production following upwelling during June-October and low dissolved oxygen in the upwelled waters, denitrification occurs in the near shore waters. Implicitly, these processes ought to bring alterations in microbial communities. Therefore, diversity and community structure of bacteria from subsurface layers of a tropical region experiencing intense seasonal lows of oxygen were analyzed through sequencing of 16S rRNA gene clones. The overall diversity was more during hypoxic period of Fall intermonsoon (FIM, October) compared either to Spring intermonsoon (SIM, March) or summer monsoon (SuM, June) months. As many as 14 lineages of bacterial domains: (37%), (21%), (20%), (3%), (3%), (2%), (2%), (7%), (2%), (1%), (1%), (0.4%), (0.2%) and (0.2%), were recognized from our coastal location. Notably, sequences of , and were found exclusively during FIM. A generally higher representation of sequences of during SuM and of and during SIM was discernible. This study is thus useful to recognize that microbial community might undergo strong temporal shifts in the monsoon affected tropical coastal ecosystems.