Low temperature S~0 biomineralization at a supraglacial springsystem in the Canadian High Arctic

摘要

Elemental sulfur (S~0) is deposited each summer onto surface ice at Borup Fiord pass on Ellesmere Island, Canada,when high concentrations of aqueous H2S are discharged from a supraglacial spring system. 16S rRNA geneclone libraries generated fromsulfur deposits were dominated by b-Proteobacteria, particularly Ralstonia sp. Sulfur-cycling micro-organisms such as Thiomicrospira sp., and e-Proteobacteria such as Sulfuricurvales and Sulfurovumalesspp. were also abundant. Concurrent cultivation experiments isolated psychrophilic, sulfide-oxidizingconsortia, which produce S~0 in opposing gradients of Na2S and oxygen. 16S rRNA gene analyses of sulfur precipitatedin gradient tubes show stable sulfur-biomineralizing consortia dominated by Marinobacter sp. in associationwith Shewanella, Loktanella, Rubrobacter, Flavobacterium, and Sphingomonas spp. Organisms closelyrelated to cultivars appear in environmental 16S rRNA clone libraries; none currently known to oxidize sulfide.Once consortia were simplified to Marinobacter and Flavobacteria spp. through dilution-to-extinction and agarremoval, sulfur biomineralization continued. Shewanella, Loktanella, Sphingomonas, and Devosia spp. werealso isolated on heterotrophic media, but none produced S~0 alone when reintroduced to Na2S gradient tubes.Tubes inoculated with a Marinobacter and Shewanella spp. co-culture did show sulfur biomineralization, suggestingthat Marinobacter may be the key sulfide oxidizer in laboratory experiments. Light, florescence and scanningelectron microscopy of mineral aggregates produced in Marinobacter experiments revealed abundant cells,with filaments and sheaths variably mineralized with extracellular submicron sulfur grains; similar biomineralizationwas not observed in abiotic controls. Detailed characterization of mineral products associated with low temperaturemicrobial sulfur-cycling may provide biosignatures relevant to future exploration of Europa and Mars.