Bacterial community structure of a coastal area in Kandalaksha Bay, White Sea, Russia: possible relation to tidal hydrodynamics

Kandalaksha Bay is an estuarine system located around the North Polar Circle in the White Sea (Russia). This peculiar environment, showing big sea level differences during tide cycles causing intense water mixing, is almost unknown concerning its microbial diversity. In this work, seawater bacterial communities, mainly obtained from a coastal area, were studied in order to gather information on their structure and most abundant populations. The study was carried out by cluster analysis of polymerase chain reaction-temperature-gradient gel electrophoresis (PCR-TGGE) fingerprinting of partial 16S-rRNA gene amplicons. Bacterial communities were strongly homogenized by tidal water mixing, especially on surface layers and close to the shore. Samples collected from the intertidal zone and the nearby sea surface grouped together with a high percentage of similarity, while those taken offshore at various depths showed evident differences. Multivariate analysis indicated depth as the most significant environmental parameter causing variations in the community structure. High levels of diversity were revealed by both the Simpson's index of diversity and the range-weighted richness index. The functional organization index suggested that the community was potentially able to preserve its functionality under stressing environmental perturbations. Sequencing of TGGE bands showed that most of the bacteria populations were evolutionarily close to alpha-proteobacteria. Some gamma-proteobacteria and Actinobacteria were revealed too. This work represents the first major contribution to understanding bacterial diversity in Kandalaksha Bay.