Microbial sulfur transformations in sediments from Subglacial Lake Whillans

Abstract

Diverse microbial assemblages inhabit subglacial aquatic environments. While few of these environments have been sampled, data reveal that subglacial organisms gain energy for growth from reduced minerals containing nitrogen, iron, and sulfur. Here we investigate the role of microbially mediated sulfur transformations in sediments from Subglacial Lake Whillans (SLW), Antarctica, by examining key genes involved in dissimilatory sulfur oxidation and reduction. The presence of sulfur transformation genes throughout the top 34 cm of SLW sediments changes with depth. SLW surficial sediments were dominated by genes related to known sulfur-oxidizing chemoautotrophs. Sequences encoding the adenosine-5′-phosphosulfate (APS) reductase gene, involved in both dissimilatory sulfate reduction and sulfur oxidation, were present in all samples and clustered into 16 distinct operational taxonomic units. The majority of APS reductase sequences (74%) clustered with known sulfur oxidizers including those within the “Sideroxydans” and Thiobacillus genera. Reverse-acting dissimilatory sulfite reductase (rDSR) and 16S rRNA gene sequences further support dominance of “Sideroxydans” and Thiobacillus phylotypes in the top 2 cm of SLW sediments. The SLW microbial community has the genetic potential for sulfate reduction which is supported by experimentally measured low rates (1.4 pmol cm-3d-1) of biologically mediated sulfate reduction and the presence of APS reductase and DSR gene sequences related to Desulfobacteraceae and Desulfotomaculum. Our results also infer the presence of sulfur oxidation, which can be a significant energetic pathway for chemosynthetic biosynthesis in SLW sediments. The water in SLW ultimately flows into the Ross Sea where intermediates from subglacial sulfur transformations can influence the flux of solutes to the Southern Ocean.

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

“…Similar sequences are found in other environmental samples including lake sediments [81,82] and in Blood Falls [8] but the organisms containing them have not been isolated or characterized. Below 8 cm, key genes involved in sulfate reduction were observed [52]. The appearance of dissimilatory sulfite reductase (dsrA) and aprA related to known sulfate-reducing prokaryotes within the genera Desulfobacterium and Desulfotomaculum indicate the potential for sulfate reduction [52].…”

“…The water column of SLW was more species rich than the surficial sediments (0-2 cm depth) containing 3931 and 2424 groups or OTUs. Cluster analysis indicated that the top 2 cm of sediments and water column were similar [7] but community structure at sediment depths below 2 cm were statistically different ( [52]; A Achberger 2015, unpublished data). The Betaproteobacteria were the most abundant bacterial division in both the water (more than 38% of sequences) and sediments (more than 59% of sequences).…”

“…Sulfate is present in excess of seawater in the top 15 cm of the SLW core, suggesting contributions from sulfur oxidation [7]. Purcell et al [52] analysed sediment samples to a depth of 34 cm and detected genes involved in S-oxidation including the adenosine-5 -phosphosulfate (APS) reductase and reverse-acting dissimilatory sulfite reductase (rDSR). Using quantitative PCR, these authors determined that aprA-containing prokaryotes were a significant portion of the community (i.e.…”

“…Nucleic acids were extracted from sediment samples as previously described [52] in a class II type A2 clean hood (LabConco model no. 3460001) using the FastDNA TM SPIN Kit (MP Biomedicals) according to the manufacturer's protocol.…”

“…Bulk sediment samples from the multi-core were collected for molecular analyses (see [52] for sampling and storage protocols). Nucleic acids were extracted from sediment samples as previously described [52] in a class II type A2 clean hood (LabConco model no.…”