Bacterial community composition in a large marine anoxic basin: a Cariaco Basin time-series survey.

Redox transition zones play a crucial role in biogeochemical cycles of several major elements. Because microorganisms mediate many reactions of these cycles, they actively participate in establishing geochemical gradients. In turn, the geochemical gradients structure microbial communities. We studied the interrelationship between the bacterial community structure and the geochemical gradient in the Cariaco Basin, the largest truly marine anoxic basin. This study's dataset includes bacterial community composition in 113 water column samples as well as the data for environmental variables (gradients of oxygen, hydrogen sulfide, sulfite, thiosulfate, ammonia, nitrate, nitrite, dissolved manganese and iron, dark CO2 fixation, and bacterial abundance) collected between 1997 and 2006. Several prominent bacterial groups are present throughout the entire water column. These include members of Gamma-, Delta-, and Epsilonproteobacteria, as well as members of the Marine Group A, the candidate divisions OP11 and Car731c. Canonical correspondence analysis indicated that microbial communities segregate along vectors representing oxygenated conditions, nitrite, nitrate and anoxic environments represented by chemoautotrophy, ammonia, sulfite, and hydrogen sulfide.