Bacterial diversity patterns of the intertidal biofilm in urban beaches of Río de la Plata

•We studied the bacterial community of intertidal biofilms by 454-pyrosequencing.•Bacterial diversity was high at all the analyzed sites.•Bacterial assemblages appeared structured mainly by salinity and dissolved oxygen (DO).•The site strongly influenced by oil refinery and having low DO clustered apart.•That sample had a high abundance of a Betaproteobacteria from Thauera genus.

Intertidal benthic ecosystems in estuaries are productive sites where microbial processes play critical roles in nutrients mineralization, primary production and trophic web. In this groundwork study we analyzed the bacterial community of intertidal biofilms from Río de la Plata beaches with different anthropogenic impacts. Several environmental parameters were measured and bacterial assemblages were analyzed by 16S-rDNA pyrosequencing. The average OTU found per sample was 527.3 ± 122.5, showing similar richness and diversity among them. However, sites having the highest and lowest salinity displayed higher bacterial diversity. Assemblages from a site nearby an oil refinery, showing the lowest salinity and oxygen concentration, were clearly distinct from the rest. The weight of this splitting relied on OTUs belonging to Thauera, known by its ability to metabolize aromatic compounds. Our results suggest that intertidal bacterial assemblages would be structured by major estuarine variables such as salinity, and that anthropogenic-induced environmental parameters might also be relevant.