Genomics of prokaryotic extremophiles to unfold the mystery of survival in extreme environments.

The organisms surviving in extreme environments deploy system support including self-protection, and energy distribution to counter extreme environmental stresses. The biological adaptations provide clues about the metabolic networks and regulatory circuits involved in their success in survival to extreme environments of these organisms. Besides this, genes and proteins of these extremophiles have gained worldwide attention of researchers, due to their immense biotechnological importance including source of novel enzymes and biomolecules for applications in industrial processes. Therefore, obtaining an insight into genomic aspects is of vital importance for basic and applied research. Genome wide studies showed that the microbes living in extreme habitats reorganize their genome using insertion, expansion or reduction of genome size, gene reshuffling through displacements and genes reorganization, G+C skewness in the genome, horizontal transfer of genes, change in polyploidy level, and preference for codon in genes that assists during adaptations to environmental extremes. For example, the comparative genomics studies revealed a significant loss of genes in acidophiles than in alkaliphiles and smaller genome size of thermophiles in comparison to psychrophiles. The genomic adaptations in halotolerance include polyploidy, battery of genes for the biosynthesis of organic osmolytes, mechanism of inorganic osmolytes acquisition and role of inorganic osmolytes and transporter system. Furthermore, it is evident that local niche specific adaptations also play a key role during adaptations to extreme environments. All these adaptations maintain extremophiles as operational units and provide them a competitive advantage over their counterparts. The review article describes the genomic multifaceted adaptation at genomic and physiological levels of extremophiles that assists in reshaping the prokaryotic extremophiles during adaptations to extreme environments to obtain a competitive edge.