Biodiversity, Adaptation and Biotechnological Importance of Bacteria Occurring in Cold Climates

This review deals with the biodiversity of cold-tolerant bacteria, also known as psychrophiles, from Antarctica, Arctic and Himalayas, strategies used by them to survive and grow at low temperature and their biotechnological potential. Bacterial abundance (5.2 × 104 to 30.7 × 108 cfu/g soil) is highest in soil (Himalayas > Antarctica > Arctic) followed by that in sediment and water. Studies involving cultivation independent methods revealed the occurrence of all major groups viz, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, Acidobacteria and Verrucomicrobia in three locations, albeit with different frequencies. Firmicutes and Acidobacterium were the dominant communities in the Himalayan soils, whereas Alphaproteobacteria and Deltaproteobacteria were found to be predominant in the Antarctic and Arctic samples. Use of cultivation-dependent methods confirmed the presence of the aforementioned groups of bacteria and led to the discovery of many new species of bacteria in the Antarctic, Arctic and Himalayan habitats. Investigations based on functional genes in conjunction with phylogenetic analysis indicate diversity in the functional genes in the bacterial taxa. The ability of psychrophilic bacteria to survive and divide at low temperature can be attributed to strategies unique to these microorganism such as the ability to catalyse reactions and continue metabolism with cold-tolerant enzymes; ability to maintain optimum membrane fluidity at low temperature; occurrence of specific genes required for survival at low temperatures; alteration in the RNA degradosome; presence of antifreeze–activity; increase in intracellular levels of ATP and alterations in DNA replication. The recently reported genome sequences of a number of novel cold-tolerant isolates are likely to provide some more insights into the mechanism of bacterial cryotolerance.