Biodiversity of prokaryotic communities in sediments of different sub-basins of the Venice lagoon

Microbial community structure and diversity in the wide and shallow Venice lagoon were assessed, before the construction of mobile dams, in nine stations representative of different four sub-basins previously selected on the basis of international guidelines for sediment quality. The sediments were mostly anoxic and colonised by microbial communities whose species richness was quantitatively correlated to total elemental sulphur and acid volatile sulphide. Automated Ribosomal Intergenic Spacer Analysis clustered the stations in three groups. One station for each group has been hence analysed in detail for bacterial and archaeal diversity by the screening of 16S rRNA gene clone libraries. The dominance of Gammaproteobacteria clones (84% with a high proportion of Vibrionaceae, indicator of urban pollution) determined a significant divergence of the station adjacent to industrial and metropolitan areas. Bacteroidetes were widespread especially where prairies of aquatic plants are located. The other two analysed stations were dominated by bacterial taxa implicated in the sulphur cycle: the anoxygenic photosynthetic Chromatiales, sulphate and sulphur reducing Desulfobacterales and Desulfuromonadales, and members of the Alpha- and Epsilonproteobacteria.