Unraveling bacterioplanktonic ecology of the estuaries of Urdaibai and Bilbao in the Bay of Biscay by high-throughput sequencing

Abstract

Planktonic communities are widely used as indicators of water pollution level, as they are vulnerableto water quality status. Indeed, it has been proposed that estuaries microbial composition changesduring eutrophication period due to the increase of pollutants and hypoxia. In the present study, wecharacterized the bacterial community structure of two macro-mesotidal estuaries by sequencing theV4 region of the 16s rDNA gene. While Bilbao estuary crosses a densely populated urban area, theUrdaibai estuary is an UNESCO biosphere reserve. Results evidenced that the bacterial speciescomposition and abundance of both estuaries significantly differed between the inner and outer watermasses. Moreover, seasonal effects on community structure were detectable in the inner zones of bothestuaries, but only minor variation were found in the outer waters, presumably due to a more stablephysicochemical environment common in open sea waters. In fact, community structure significantlydiffered in this period, suggesting a low turnover time for inner water mass in this estuary. Moreover,it has been observed that the bacterial metabolism is different in each of water mass, especially in themass of eutrophic water and in the waters around the WWTP of Bilbao.