Abstract
Ice-binding proteins (IBPs) have been isolated from various sea-ice organisms. Their characterisation points to a crucial role in protecting the organisms in sub-zero environments. However, their in situ abundance and diversity in natural sea-ice microbial communities is largely unknown. In this study, we analysed the expression and phylogenetic diversity of eukaryotic IBP transcripts from microbial communities of Arctic and Antarctic sea ice. IBP transcripts were found in abundances similar to those of proteins involved in core cellular processes such as photosynthesis. Eighty-nine percent of the IBP transcripts grouped with known IBP sequences from diatoms, haptophytes and crustaceans, but the majority represented novel sequences not previously characterized in cultured organisms. The observed high eukaryotic IBP expression in natural eukaryotic sea ice communities underlines the essential role of IBPs for survival of many microorganisms in communities living under the extreme conditions of polar sea ice.
Highlights
The proteins change the microstructure of sea ice, helping to retain more liquid brine and making it more habitable to the microorganisms (Bayer-Giraldi et al, 2011; Krembs et al, 2011; Raymond and Kim, 2012)
Sanger sequenced metatranscriptomes (Supplementary Table 1) were established from RNA collected from Arctic sea ice (Kongsfjord, Svalbard: Arctic sample (ARC), organism size 1.2–200 μm) and Antarctic sea ice (Dumont dUrville Sea: ANT-A1, ANT-A2, organism size 0.2–50 μm; Weddell Sea: ANT-B1, ANT-B2, organism size 41.2 μm)
A replicate of the samples ANT-B1/B2 was sequenced with Roche (Rotkreuz, Switzerland) 454 GS-FLX (NERC sequencing facility, Liverpool, UK) and GS-Titanium (Roche 454, Branford, CT, USA) techniques by Toseland et al (2013)
Summary
The proteins change the microstructure of sea ice, helping to retain more liquid brine and making it more habitable to the microorganisms (Bayer-Giraldi et al, 2011; Krembs et al, 2011; Raymond and Kim, 2012). IBPs were shown to be highly expressed both at the transcript and protein level in two diatom species under laboratory conditions resembling sea ice (Bayer-Giraldi et al, 2010, 2011).
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