N-124. Spatial and Temporal Distribution of Cariaco Basin Bacterial Communities in Relation to Biogeochemical Gradients

M. Rodriguez-Mora1, A. Chistoserdov1, X. N. Li2, M. I. Scranton2, G. T. Taylor2, X. Lin3;
1Univ. of Louisiana, Lafayette, LA, 2Stony Brook Univ., Stony Brook, NY, 3Stroud Water Res. Ctr,, Avondale, PA.

Oxic-anoxic transition zones play a crucial role in biogeochemical cycles of several elements in the ocean. Because microorganisms mediate many reactions of these cycles, they actively participate in establishing geochemical gradients. In turn, the geochemical gradients structure microbial communities across the oxic-anoxic transition zones. Using canonical correspondence analysis (CCA), we studied the interrelationship between the microbial community structure and geochemical gradient in the Cariaco Basin, the largest true marine redox transition zone in the ocean water column. A dataset used in the study included the composition of microbial community in 113 water column samples as well as the data for the environmental variables (gradients of O2, H2S, ammonia, nitrate, nitrite, dissolved Mn, dark CO2 fixation and bacterial abundance) collected in 1997-2006. CCA indicated that the microbial communities were separated along the vectors representing oxygen, the suboxic gradients (nitrite, nitrate) and the anoxic gradients represented by the chemoautotrophy, ammonia, dissolved manganese and H2S vectors. The weighted averages of the samples with respect to hydrogen sulfide and chemoautotrophy result in close rankings. Due to strong correlation between chemolithotrophy and sulfide profiles we conclude that chemolithotrophy is to large extent is fueled by oxidation of sulfide or sulfide oxidation product. The bacterial abundance was not a defining factor in microbial community composition and did not correlate with any other environmental factors. Although we observed several prominent bacterial groups to be present across the whole depth profile (a specific uncultured γ-proteobacterium and δ-proteobacterium), most bacterial groups are highly specific to their specific redox environment (e.g., Pelagibacter ubique is only found in oxic and suboxic zones; ε-proteobacteria in suboxic and anoxic zones). Yet other groups, such as the candidate OP11-associated division, were represented by different ecotypes in oxic anoxic, suboxic and anoxic zones.