Distinctive microbial communities in subzero hypersaline brines from Arctic coastal sea ice and rarely sampled cryopegs

Abstract

Hypersaline aqueous environments at subzero temperatures are known to be inhabited by microorganisms, yet information on community structure in subzero brines is very limited. Near Utqiaġvik, Alaska, we sampled subzero brines (–6°C, 115–140 ppt) from cryopegs, i.e. unfrozen sediments within permafrost that contain relic (late Pleistocene) seawater brine, as well as nearby sea-ice brines to examine microbial community composition and diversity using 16S rRNA gene amplicon sequencing. We also quantified the communities microscopically and assessed environmental parameters as possible determinants of community structure. The cryopeg brines harbored surprisingly dense bacterial communities (up to 108 cells mL–1) and millimolar levels of dissolved and particulate organic matter, extracellular polysaccharides and ammonia. Community composition and diversity differed between the two brine environments by alpha- and beta-diversity indices, with cryopeg brine communities appearing less diverse and dominated by one strain of the genus Marinobacter, also detected in other cold, hypersaline environments, including sea ice. The higher density and trend toward lower diversity in the cryopeg communities suggest that long-term stability and other features of a subzero brine are more important selective forces than in situ temperature or salinity, even when the latter are extreme.

Viral Ecogenomics of Arctic Cryopeg Brine and Sea Ice

“…These results indicate that the cryopeg brine supports a unique viral community (consistent with a previous study [15]), which may be due to this cryopeg system having been separated from the atmosphere and meteoric water for at least 14,000 years and possibly much longer (9,17,18). Viral communities inhabiting the middle and top layers of the ice core were similar to each other and to that of sea-ice brine, as expected given that this brine was drained from these two sea-ice layers.…”

“…Microbial communities in sea ice and cryopegs have been investigated previously in many studies. Taxonomically, Proteobacteria and Bacteroidetes dominate PCR-based amplicon sequencing of both types of brine (7,9). For example, in one comparative study, cryopeg brines were dominated by Gammaproteobacteria and Bacteroidia, with average relative abundances of 57% and 22%, respectively, while sea-ice brines were dominated by Bacteroidia (average relative abundance of 51%) followed by Gammaproteobacteria (average relative abundance of 30%) (9).…”

“…Taxonomically, Proteobacteria and Bacteroidetes dominate PCR-based amplicon sequencing of both types of brine (7,9). For example, in one comparative study, cryopeg brines were dominated by Gammaproteobacteria and Bacteroidia, with average relative abundances of 57% and 22%, respectively, while sea-ice brines were dominated by Bacteroidia (average relative abundance of 51%) followed by Gammaproteobacteria (average relative abundance of 30%) (9). Although some microbes may only be dormant in these systems (19), studies have documented active microbial communities in sea ice (reviewed in reference 8) and cryopeg brines (9,11,15).…”

“…For example, in one comparative study, cryopeg brines were dominated by Gammaproteobacteria and Bacteroidia, with average relative abundances of 57% and 22%, respectively, while sea-ice brines were dominated by Bacteroidia (average relative abundance of 51%) followed by Gammaproteobacteria (average relative abundance of 30%) (9). Although some microbes may only be dormant in these systems (19), studies have documented active microbial communities in sea ice (reviewed in reference 8) and cryopeg brines (9,11,15). Thus, at least some microbes in these environments have adapted to the extremely cold and saline conditions and are contributing to ecosystem functioning and biogeochemical cycling.…”

Microbiota entrapped in recently-formed ice: Paradana Ice Cave, Slovenia

“…Cold ecosystems include deep oceans, polar regions, high mountains and subterranean caves with a large variety of aquatic and terrestrial ecosystems 1 . In recent years, cold habitats such as glaciers and ice sheets 2 , sea ice 3 , lake ice 4 and permafrost 5 have received most attention as regards microbiological studies, mainly because of their sensitivity to climate change. Also, there is a growing research interest related to frozen ecosystems as analogues of extraterrestrial habitats 6 .…”