Comparative genomics study of completely sequenced Thermus sp. strains to enhance and facilitate their application in biotechnology

Abstract

Thermus bacteria are of special interest because of their ability to live in high temperature environments. Their enzymes exhibit higher and stable activity in industry as compared to mesophilic or synthetic counterparts. Thermus bacteria are capable of reducing heavy metals which is essential in eradication of heavy metal pollution and controlling global warming. Genome rearrangements were investigated in Thermus species and the extent to which they affected the distribution of functionally related genes on the chromosome and its implication on the coherence of the metabolic network. The contribution of horizontal gene transfer to genome rearrangements and the shuffling of genes on the chromosome were analysed. Horizontally transferred genes were identified alongside their donors and recipients, their age and relative time of insertion. Metabolic networks were clustered and compared to determine the extent to which they were affected by rearrangements as a measure of evolutionary pressures experienced by organisms. Factors that enhance protein thermostability were analysed by determining dominant substitutions for amino acid residues and their properties. Protein thermostability was measured using the UNAFold algorithm. Amino acid substitutions were compared between less and highly thermophilic orthologous sequences in T. scotoductus SA-01 and T. thermophilus HB27 respectively. Protein structures were modelled for orthologs that met a defined selection criterion. Dominant amino acid substitutions were analysed in the structures to determine their locations. The contribution of dominant substitutions to energy changes in structures was analysed using FoldX program. Results revealed a uniform distribution of functionally related genes among thermophilic and mesophilic organisms. The contribution of horizontal gene transfer to genome rearrangements was found to be insignificant. Metabolic networks for Thermus species were poorly clustered in correlation with their optimum environmental growth temperatures. Non-polar, small and charged amino acids were found to significantly enhance thermostability. Higher occurrence of alanine substituted by serine and threonine; and arginine substituted by glutamine and lysine were observed to influence thermostability. Structural comparison showed that mutations were mostly located on the surfaces and helices of structures. The positions of mutations appeared to influence their energy contribution to the overall structure as measured by FoldX algorithm.