Bacterial Community Structure in Coastal Marine Sediments, Assessed by Pyrosequencing of 16S rRNA Genes

MARCOS, M.S.; LOZADA, M; GIL, M.N; DI MARZIO, W.D; DIONISI, H.M

Villa Cárlos Paz

Congreso; VI Congreso Argentino de Microbiología General; 2009

Sociedad Argentina de Microbiología General (SAMIGE)

Marine bacteria drive globally important biogeochemical cycles and have a major role determining the environmental quality of marine ecosystems. Marine sediments can act as a trap of hydrophobic contaminants, and they may become sufficiently polluted to disrupt these essential biological processes. The aim of this study was to analyze bacterial community structure in coastal sediments of Patagonia in the context of environmental variation. This project is part of the International Census of Marine Microbes initiative. Composite intertidal sediment samples were retrieved at two sites with a different history of hydrocarbon exposure: Fracasso Beach (FB), located in the protected natural area of Valdes Peninsula, and Cordova Cove (CC), near Comodoro Rivadavia and close to oil exploitation activities. The measured physico-chemical parameters include pH, temperature, oxidation-reduction potential, granulometry, organic matter, as well as ammonia and polycyclic aromatic hydrocarbon (PAH) concentrations. Pyrosequencing of the V6 hypervariable region of 16S rRNA genes from Bacteria was performed at the Marine Biological Laboratory in Woods Hole, USA, using a GS20 system (Roche). Rarefaction curves, species richness indexes (ACE and Chao1) and taxonomical assignment of V6 sequences were performed by using the VAMPS interface (Visualization and Analysis of Microbial Population Structures). Both sediment samples differed markedly in their total PAH concentration (FB: not detected, CC: 758 mg kg-1 dry sediment), particle sizes, ammonia concentrations and organic matter content. The polluted sediment contained a lower ammonia concentration, suggesting the existence of a nutrient limitation in this environment. Although almost 60,000 bacterial V6 sequences were obtained from both samples, rarefaction curves still show that additional sampling would be needed to estimate total number of OTUs present in each sample. These results are an evidence of the vast diversity of bacterial communities indigenous of coastal sediments. Species richness indexes ACE and Chao1 were 20% higher in CC than in FB, suggesting that microbial diversity in CC is not being affected by its exposure to anthropogenic pollutants. Community composition was similar in both samples at the Phylum level, although differences were found at lower taxonomic resolution. In both samples Gammaproteobacteria was the dominant group within the Phylum Proteobacteria, followed by Alphaproteobacteria or Deltaproteobacteria in the non-polluted and impacted sample, respectively. In this study, we used next-generation sequencing to deeply characterize the bacterial community structure in coastal marine sediments, with an extensive analysis of metadata. The characterization of microbial communty structure is the starting point for understanding ecological and environmental processes shaping the microbial communities in the marine environment.