Heterotrophic and autotrophic microbial populations in cold perennial springs of the high arctic

Abstract

The saline springs of Gypsum Hill in the Canadian high Arctic are a rare example of cold springs originating from deep groundwater and rising to the surface through thick permafrost. The heterotrophic bacteria and autotrophic sulfur-oxidizing bacteria (up to 40% of the total microbial community) isolated from the spring waters and sediments were classified into four phyla (Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria) based on 16S rRNA gene analysis; heterotrophic isolates were primarily psychrotolerant, salt-tolerant, facultative anaerobes. Some of the isolates contained genes for thiosulfate oxidation (soxB) and anoxygenic photosynthesis (pufM), possibly enabling the strains to better compete in these sulfur-rich environments subject to long periods of illumination in the Arctic summer. Although leucine uptake by the spring water microbial community was low, CO(2) uptake was relatively high under dark incubation, reinforcing the idea that primary production by chemoautotrophs is an important process in the springs. The small amounts of hydrocarbons in gases exsolving from the springs (0.38 to 0.51% CH(4)) were compositionally and isotopically consistent with microbial methanogenesis and possible methanotrophy. Anaerobic heterotrophic sulfur oxidation and aerobic autotrophic sulfur oxidation activities were demonstrated in sediment slurries. Overall, our results describe an active microbial community capable of sustainability in an extreme environment that experiences prolonged periods of continuous light or darkness, low temperatures, and moderate salinity, where life seems to rely on chemolithoautotrophy.

FIG. 1.

Culturable microbial counts (CFU/g) obtained by the spread plate method on heterotrophic (M2216, AH-H2, and AH-H8) and thiosulfate (AH-S2) media for the GH spring sediments.

FIG. 2.

Phylogenetic relationships of 16S rRNA gene sequences from the GH springs' bacterial isolates (in boldface type) related to the Actinobacteria, Bacteroidetes, and Firmicutes. The tree was inferred by neighbor-joining analysis of 1,018 homologous positions of sequence from each isolate. Numbers on the nodes are the bootstrap values (percentages) based on 1,000 replicates. The scale bar indicates the estimated number of base changes per nucleotide sequence position.

FIG. 3.

Phylogenetic relationships of 16S rRNA gene sequences from the GH springs' bacterial isolates (in boldface type) related to the Proteobacteria. The tree was inferred by neighbor-joining analysis of 827 homologous positions of sequence from each isolate. Numbers on the nodes are the bootstrap values (percentages) based on 1,000 replicates. The scale bar indicates the estimated number of base changes per nucleotide sequence position.

FIG. 4.

Neighbor-joining tree based on 465 nucleotide positions of the soxB gene from the GH springs' bacterial isolates (in boldface type). Numbers on the nodes are the bootstrap values (percentages) based on 1,000 replicates. The scale bar indicates the estimated number of base changes per nucleotide sequence position.

FIG. 5.

Neighbor-joining tree based on 184 nucleotide positions of the pufM gene from the GH springs' bacterial isolates (in boldface type). The scale bar indicates the estimated number of base changes per nucleotide sequence position. The bootstrap values were lower than 50 and are not indicated on the nodes.

FIG. 6.

Evolution of the sulfate concentration (ppm) in microcosms for the GH-4 spring sediment. (a) 2006 aerobic microcosms. ▴, S₂O₃/molybdate (Mo); ▪, S₂O₃; dashed line, unamended; ○, S₂O₃, autoclaved. (b) 2007 aerobic microcosms. ▵, 2.5% NaCl at RT under light incubation; ▴, 2.5% NaCl at RT under dark incubation; ♦, 2.5% NaCl at 5°C under dark incubation; □, 7.5% NaCl at RT under light incubation; •, 7.5% NaCl at 5°C under dark incubation; ▪, 7.5% NaCl at RT under dark incubation. (c) 2006 anaerobic microcosms. □, lactate/Mo; ▪, lactate; ▵, Mo; dashed line, unamended. The error bars represent the standard errors.