Modelled and measured dynamics of viruses in Arctic winter sea‐ice brines

Abstract

We describe a model based on diffusion theory and the temperature-dependent mechanism of brine concentration in sea ice to argue that, if viruses partition with bacteria into sea-ice brine inclusions, contact rates between the two can be higher in winter sea ice than in seawater, increasing the probability of infection and possible virus production. To examine this hypothesis, we determined viral and bacterial concentrations in select winter sea-ice horizons using epifluorescence microscopy. Viral concentrations ranged from 1.6 to 82 x 10(6) ml(-1) of brine volume of the ice, with highest values in brines from coldest (-24 to -31 degrees C) ice horizons. Calculated virus-bacteria contact rates in underlying -1 degrees C seawater were similar to those in brines of -11 degrees C ice but up to 600 times lower than those in ice brines at or below -24 degrees C. We then incubated native bacterial and viral assemblages from winter sea ice for 8 days in brine at a temperature (-12 degrees C) and salinity ( approximately 160 psu) near expected in situ values, monitoring their concentrations microscopically. While different cores yielded different results, consistent with known spatial heterogeneity in sea ice, these experiments provided unambiguous evidence for viral persistence and production, as well as for bacterial growth, in -12 degrees C brine.

Characterization of a cold-active bacteriophage on two psychrophilic marine hosts

“…3B) compared to ~10 d for P. ingrahamii at -12°C. These results parallel experimental evidence from winter sea-ice brines for bacterial metabolic activity at -2 to -20°C (Junge et al 2004) and viral production and bacterial growth at -12°C (Wells & Deming 2006a). Significant production of 9A at -10°C was not observed (by PFU assay) in frozen samples, possibly due to impingement of host cells by ice crystals or to high salinities in liquid brine inclusions where cells and viruses presumably partitioned.…”

“…The intention of the first experiment between -10 and -12°C was to measure phage production in a frozen sample, presumably within the brine inclusions formed during freezing (Junge et al 2001, Wells & Deming 2006a. Surprisingly, only about half of the experimental samples froze, even after 15 d. Failure to freeze may reflect an absence of ice-nucleation events: in this case, neither 34H nor 9A has substantial icenucleating ability (K. Junge pers.…”

“…Spencer (1955Spencer ( , 1960Spencer ( , 1963, in particular, demonstrated phage infection of indigenous marine bacteria (rather than enteric hosts) specifically under conditions mimicking those in situ (3 to 4% salinity and 0°C). Later workers have generally remained attentive to use of seawater salinities for marine phage-host cultivation but have overlooked Spencer's (1955Spencer's ( , 1960Spencer's ( , 1963 emphasis on temperature, despite the predominance of cold waters (≤ 4°C) at depth and high latitudes, as well as mounting evidence that viruses play active ecological roles in cold waters (Steward et al 1996, GuixaBoixereu et al 2002, Wells & Deming 2006b) and sea ice (Wells & Deming 2006a).…”

Microbial diversity and activity in hypersaline high Arctic spring channels

“…In addition to prolonged exposure to subzero temperatures, microbial communities existing in such cryoenvironments must overcome extremely low rates of nutrient and metabolite transfer, high solute concentrations, low water activity, and potentially high background radiation (Ayala-del-Rio et al 2010;Bakermans 2008;Steven et al 2006). Nevertheless, microbial diversity, ecology and activity have been recently described in numerous cryoenvironment habitats and generally indicate that viable microbial communities consisting of bacteria, archaea, viruses, and eukaryotes exist in these extreme habitats (Bakermans 2008(Bakermans , 2012Priscu and Christner 2004;Steven et al 2006;Wells and Deming 2006;and reviewed in Margesin and Miteva 2011) and are capable of both growth and metabolic activity at ambient subzero temperatures (Anesio et al 2007;Bakermans 2012;Bottos et al 2008;D'Amico et al 2006;Niederberger et al 2010;Steven et al 2008). Cold-adapted microorganisms inhabiting such environments exhibit a variety of modifications to their proteins, nucleic acids, and membranes, which allow them to maintain their fluidity, flexibility and associated activity at low temperatures, as well as other adaptations including cryoprotectant production, and highly efficient regulation of growth (Ayala-del-Rio et al 2010;Bakermans 2008).…”

Status and trends in the structure of Arctic benthic food webs

“…Increased impact of algal viruses and parasites would decrease the amount of food available for pelagic and benthic grazers. How these processes affect current blooms in the Arctic Ocean remains largely unknown, but both viruses and parasitic Syndiniales have been reported from sea ice (Wells & Deming 2006;Bachy et al 2011;Collins & Deming 2011;Comeau et al 2013;Piwosz et al 2013) and the water column (HowardJones et al 2002;Lovejoy et al 2006;Bachy et al 2011;Comeau et al 2011;Payet & Suttle 2013).…”