from Ahmad Iskandar Bin Haji Mohd Taha, Rifat Zubair Ahmed, Taro Motoigi, Kentaro Watanabe, Norio Kurosawa and Hidetoshi Okuyama writing in Cold-Adapted Microorganisms:

Ever since Escherichia coli, which is a mesophilic bacterium, was found to adjust its membrane fluidity in a liquid crystalline state by modulating fatty acid composition and the designation of this process as homeoviscous or homeophasic adaptation, numerous analogous phenomena have been reported in cold-adapted bacteria [psychrophilic or psychrotrophic (psychrotolerant) bacteria]. Unsaturation, which includes the biosynthesis of monounsaturated or long-chain polyunsaturated fatty acids and branched fatty acids, and branched-chain formation are the most important types of fatty acid modulation in psychrophilic and psychrotrophic (psychrotolerant) bacteria. The distribution of these fatty acids is not restricted to cold-adapted microorganisms: rather, it appears to depend on bacterial diversity (Gram- positive or negative) and/or habitat (terrestrial or marine environment) than on temperature. Eicosapentaenoic acid, which has been detected only in marine Gram-negative bacteria, had been regarded to confer significant membrane fluidity in bacteria, but it is now considered that it may also have a function in antioxidation or membrane modulation by constraining membrane fluidity. The mode of fatty acid modulation is unlikely to differ between psychrophilic and psychrotrophic bacteria, which had narrower and wider growth temperature ranges, respectively. The sole difference seems to be higher capacity to modulate fatty acid composition in psychrotrophic bacteria than in psychrophilic bacteria.

Further reading: Cold-Adapted Microorganisms

from Katayama Taiki and Michiko Tanaka writing in Cold-Adapted Microorganisms:

Bacteria and fungi preserved for long periods at sub-zero temperatures in Alaskan and Siberian permafrost ice wedge were reactivated on agar by aerobic cultivation at 15°C. Culturable bacteria differed among ice samples, but several phylogenetic groups were closely related to those in other frozen environments. Incubation under controlled temperatures and the Arrhenius profiles of bacterial isolates from the Alaskan ice wedge indicated that they could grow at temperatures below 0°C without remarkable alterations in their cellular process. The novel ice wedge isolates, Glaciibacter superstes AHU1791T and Tomitella biformata AHU1821T, increased membrane fluidity at lower to subzero temperatures by modulating the fatty acid composition of the cytoplasmic membrane. Reactivating the non-culturable state of ice wedge isolates using resuscitation promoting factor (Rpf) and culturing melted ice wedge with Rpf provided indirect evidence that non-culturable bacteria exist within the ice wedge in situ. Bacteria in ice wedges can change their membrane fatty acid composition and/or structure to survive, but may then lose the ability to grow under laboratory conditions, as a final adaptation to long periods in a frozen natural environment.

Further reading: Cold-Adapted Microorganisms

from Kazuaki Yoshimune, Jun Kawamoto and Tatsuo Kurihara writing in Cold-Adapted Microorganisms:

This chapter primarily describes cold shock proteins (CSPs), which are induced in response to temperature downshift in both psychrophiles and mesophiles. These proteins are important for various cellular processes, including transcription, translation, protein synthesis and folding, and membrane functions, to maintain their viability under cold conditions. Here, the CSPs in psychrophilic and mesophilic microorganisms are represented on the basis of the results of proteome analyses. In particular, CSPs that were isolated from the Antarctic psychrophile Shewanella livingstonensis Ac10 are described in detail. A number of microorganisms induce molecular chaperones in response to the cold, although the majority of chaperones are induced as a result of heat shock. Chaperones with peptidyl prolyl cis-trans isomerase activity are often induced by cold to accelerate protein folding by interconverting the cis and trans isomers of proline imidic peptide bonds, and these cold shock chaperones are also discribed here. Cold adapted proteins often have higher flexibility as compared to mesophilic proteins. The features of cold adapted proteins are briefly described. Finally, the production of recombinant proteins in psychrophiles is shown to suggest a future application of psychrophiles.

Further reading: Cold-Adapted Microorganisms

from Yuichi Nogi writing in Cold-Adapted Microorganisms:

Psychrophilic microorganisms are extremophiles that are capable of growth and reproduction at low temperatures. They are present in marine environments, which occupy slightly more than 70% of Earth's surface, especially in the Arctic, Antarctica, and deep seas at temperatures lower than 15°C. Marine psychrophiles utilize a wide variety of metabolic pathways, including photosynthesis, chemoautotrophy, and heterotrophy. The deep-sea bacteria called psychropiezophiles "love" both high pressure and low temperature. Marine psychrophiles are characterized by lipid cell membranes chemically resistant to hardening in response to the cold. Most psychrophiles are Bacteria, and psychrophily is present in widely diverse microbial lineages within the broad groups of Alpha-, Beta-, Delta-, and Gammaproteobacteria and the Bacteroidetes phylum.

Further reading: Cold-Adapted Microorganisms