skafta2006
An oligarchic microbial assemblage in the anoxic bottom waters of a volcanic subglacial lake
In 2006, we sampled the anoxic bottom waters of a volcanic lake beneath the Vatnajökull ice cap (Iceland).  The sample contained 5 10^5 cells/ml^-1 and whole-cell fluorescent in situ hybridization (FISH) and polymerase chain reaction with domain-specific probes showed these to be essentially all bacteria, with no detectable archaea.  Pyrosequencing of the V6 hypervariable region of the 16S ribosomal RNA gene, Sanger sequencing of a clone library, and FISH-based enumeration of four major phylotypes revealed that the assemblage was dominated by a few groups of putative chemotrophic bacteria whose closest cultivated relatives use sulfide, sulfur, or hydrogen as electron donors, and oxygen, sulfate, or CO_2 as electron acceptors.  Hundreds of other phylotypes are present at lower abundance in our V6 tag libraries and a rarefaction analysis indicates that sampling did not reach saturation, but FISH data limit the remaining biome to <10-20% of all cells. The composition of the oligarchy can be explained if mixing of sulfidic lake water and oxygenated glacial meltwater supported the growth of microaerobic sulfide and hydrogen oxidizers and suppressed the growth of methanogens  in favor of acetogens.       454 sequence data is available from the Short Read Archive (SRA): <a href="ftp://ftp.ncbi.nih.gov/pub/TraceDB/ShortRead/SRA002254  ">SRA002254</a>.