Phylogenetic diversity of transition and anoxic zone bacterial communities within a near-shore anoxic basin: Nitinat Lake

Abstract

Summary At two stations surveyed in Nitinat Lake, a ∼200-m-deep anoxic tidal fjord, sulfide was detected as close as 15 m from the surface. Biological characterization, determined from small subunit ribosomal RNA gene sequencing, of the chemocline and anaerobic zone revealed many sequences related to sulfur-oxidizing bacteria, suggesting that sulfur cycling is a dominant process. γ- and ε-Proteobacteria related to thiotrophic symbionts, as well as Chlorobium sp., dominated the transition zone. These are expected to play a role in dark and phototrophic CO2 fixation, respectively. ε-Proteobacteria phylotype abundance increased with depth, eventually comprising 69-97% of all sequences recovered from the anoxic zone. The vast majority (74%) of these phylotypes were affiliated with a novel Acrobacter sp. group (NITEP5). Quantification of NITEP5 revealed that up to 2.8 × 10 5 cells ml-1 were present in the anoxic zone. Surprisingly, although sequences related to known sulfate-reducing bacteria were recovered from the transition zone, quantification of the dsr gene and 35SO42- uptake tests suggest that sulfate-reduction within the water column is negligible. Overall, sequence diversity between different vertical zones was high, although the spatial segregation of γ-Proteobacteria, Chlorobi, and ε-Proteobacteria did not appear to vary significantly between seasons. © 2009 Society for Applied Microbiology and Blackwell Publishing Ltd.