Upwelling induced changes in the abundance and community structure of archaea and bacteria in a recurring mud bank along the southwest coast of India

The present study reports the influence of upwelling on the abundance and community structure of archaea and bacteria in a mud bank formed along the coastal waters of Alappuzha, the southwest coast of India. The signatures of upwelling were observed with the onset of southwest monsoon, characterized by a decrease in sea surface temperature and dissolved oxygen in bottom waters and increase in salinity. Nitrite, nitrate, and phosphate showed a significant increase during upwelling compared to pre-upwelling conditions. There were no significant differences in the abundance of archaea across seasons (pre- and during upwelling conditions) and regions (Station S1, inside and Station S2, outside the mud bank), while the bacterial abundance showed a six-fold increase for S1 and four-fold increase for S2 during upwelling. The PCR–DGGE results show the existence of a transient population of archaea and bacteria in the mud bank region during upwelling. The step up multiple regression models could explain 66.5% and 56.3% of the temporal variations in archaeal and 96.5% and 53.63% in bacterial distribution inside and outside of mud bank respectively, at pre-upwelling conditions. About 67% of the temporal variations in the distribution of archaea and 41.4% in bacteria inside and 49.9% in bacteria outside of mud bank during upwelling conditions could be explained by the same model. The temporal variation in the distribution of archaea outside mud bank during upwelling conditions could not be explained by the present regression model. Our studies indicate that the upwelling induces changes in the abundance and community structure of bacteria in the mudbank, which are modulated by the interactive effects of hydrographic variables. Further studies to unravel the interactive effect of hydrographic variables on the biogeochemical activities of microorganisms would be appreciated.