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Metagenomic library screening, by functional or sequence analysis, has become an established method for the identification of novel genes and gene products, including genetic elements implicated in microbial stress response and adaptation. We have identified, using a sequence-based approach, a fosmid clone from an Antarctic desert soil metagenome library containing a novel gene which codes for a protein homologous to a Water Hypersensitivity domain (WHy). The WHy domain is typically found as a component of specific LEA (Late Embryogenesis Abundant) proteins, particularly the LEA-14 (LEA-8) variants, which occur widely in plants, nematodes, bacteria and archaea and which are typically induced by exposure to stress conditions. The novel WHy-like protein (165 amino acid, 18.6 kDa) exhibits a largely invariant NPN motif at the N-terminus and has high sequence identity to genes identified in Pseudomonas genomes. Expression of this protein in Escherichia coli significantly protected the recombinant host against cold and freeze stress., (© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

An Antarctic sea ice bacterium of the Gram-negative genus Colwellia, strain SLW05, produces an extracellular substance that changes the morphology of growing ice. The active substance was identified as a approximately 25-kDa protein that was purified through its affinity for ice. The full gene sequence was determined and was found to encode a 253-amino acid protein with a calculated molecular mass of 26,350 Da. The predicted amino acid sequence is similar to predicted sequences of ice-binding proteins recently found in two species of sea ice diatoms and a species of snow mold. A recombinant ice-binding protein showed ice-binding activity and ice recrystallization inhibition activity. The protein is much smaller than bacterial ice-nucleating proteins and antifreeze proteins that have been previously described. The function of the protein is unknown but it may act as an ice recrystallization inhibitor to protect membranes in the frozen state.

Shewanella sp. Ac10 is a psychrotrophic bacterium isolated from the Antarctica that actively grows at such low temperatures as 0 degrees C. Immunoblot analyses showed that a heat-shock protein DnaK is inducibly formed by the bacterium at 24 degrees C, which is much lower than the temperatures causing heat shock in mesophiles such as Escherichia coli. We found that the Shewanella DnaK (SheDnaK) shows much higher ATPase activity at low temperatures than the DnaK of E. coli (EcoDnaK): a characteristic of a cold-active enzyme. The recombinant SheDnaK gene supported neither the growth of a dnaK-null mutant of E. coli at 43 degrees C nor lambda phage propagation at an even lower temperature, 30 degrees C. However, the recombinant SheDnaK gene enabled the E. coli mutant to grow at 15 degrees C. This is the first report of a DnaK supporting the growth of a dnaK-null mutant at low temperatures.