Bacterial Activity at −2 to −20°C in Arctic Wintertime Sea Ice

Abstract

Arctic wintertime sea-ice cores, characterized by a temperature gradient of ؊2 to ؊20°C, were investigated to better understand constraints on bacterial abundance, activity, and diversity at subzero temperatures. With the fluorescent stains 4,6-diamidino-2-phenylindole 2HCl (DAPI) (for DNA) and 5-cyano-2,3-ditoyl tetrazolium chloride (CTC) (for O 2 -based respiration), the abundances of total, particle-associated (>3-m), freeliving, and actively respiring bacteria were determined for ice-core samples melted at their in situ temperatures (؊2 to ؊20°C) and at the corresponding salinities of their brine inclusions (38 to 209 ppt). Fluorescence in situ hybridization was applied to determine the proportions of Bacteria, Cytophaga-Flavobacteria-Bacteroides (CFB), and Archaea. Microtome-prepared ice sections also were examined microscopically under in situ conditions to evaluate bacterial abundance (by DAPI staining) and particle associations within the brine-inclusion network of the ice. For both melted and intact ice sections, more than 50% of cells were found to be associated with particles or surfaces (sediment grains, detritus, and ice-crystal boundaries). CTC-active bacteria (0.5 to 4% of the total) and cells detectable by rRNA probes (18 to 86% of the total) were found in all ice samples, including the coldest (؊20°C), where virtually all active cells were particle associated. The percentage of active bacteria associated with particles increased with decreasing temperature, as did the percentages of CFB (16 to 82% of Bacteria) and Archaea (0.0 to 3.4% of total cells). These results, combined with correlation analyses between bacterial variables and measures of particulate matter in the ice as well as the increase in CFB at lower temperatures, confirm the importance of particle or surface association to bacterial activity at subzero temperatures. Measuring activity down to ؊20°C adds to the concept that liquid inclusions in frozen environments provide an adequate habitat for active microbial populations on Earth and possibly elsewhere.The constraints on and sustainability of life in frozen environments are of considerable importance in a number of contexts, from polar microbial ecology and astrobiology to cryopreservation and other industrial applications (42). For example, a number of subzero environments, such as Antarctic and Arctic lakes (23,25,38), snow (3), glacial ice (46), and permafrost soils (41), have been investigated as Earth analogs for potential extraterrestrial habitats also at subzero temperatures. To date, fundamental questions underlying the behavior of bacteria in any frozen environment have not been adequately addressed: how do bacteria manage to persist and possibly remain active? At the lowest temperatures observed on Earth, what environmental factors enable and control bacterial survival and even sustained activity?This study focused on Arctic wintertime sea ice, the coldest marine habitat on Earth (temperature range of Ϫ2 to Ϫ35°C) (31) and an important component of polar climate and ecos...

Hydrocarbon biodegradation by Arctic sea-ice and sub-ice microbial communities during microcosm experiments, Northwest Passage (Nunavut, Canada)

“…High degradation rates could be found in the field for several other low pour-point oils, although in some cases oil composition could lead to divergent results. In ice-covered areas however, where temperature in first-year ice varies between -2 and -20°C (Junge et al 2004), degradation rates would potentially be much lower than what was observed in ice microcosms because only 39% of the ITOPF-classified oils would exhibit liquid characteristics below -15°C. At temperature as low as -25 °C in multi-year ice (Perovich & Elder 2001), biodegradation rates would be negligible, if not null, because most oils will solidify (ITOPF 2011) and because very cold ice has little brine volume fraction and thus, fewer microhabitats to support an active bacterial community (Deming 2010).…”

“…In winter, chances are that sea ice would be impermeable because the temperature can drop below -5 °C (Junge et al 2004). This means that oil spilled on the ice cover would not percolate and be in contact with bottom-ice bacterial communities, thereby limiting biodegradation.…”

Microbial community changes along the Ecology Glacier ablation zone (King George Island, Antarctica)

“…The amount of particulate material correlated positively with microbial abundance and functional diversity, whereas CaCO 3 concentration corresponded with bacterial phylogenetic diversity. The beneficial role of particulates for microbial activity have been previously recorded for polar aquatic habitats (Junge et al 2004).…”

Diffusion-controlled metabolism for long-term survival of single isolated microorganisms trapped within ice crystals

“…Junge et al showed that many microorganisms in sea ice occupy brine channels (2) and that many in lake ice occupy veins (3). Mader et al (4) showed that both bacteria and fluorescent beads added to water used to make ice are rejected from the solid phase and incorporated into liquid veins, provided that they are small enough to fit, whereas beads larger than the vein diameter are frozen into solid ice.…”