Comparative analysis to identify determinants of changing life style in Thermosynechococcus elongatus BP-1, a thermophilic cyanobacterium.

A comparative genomics analysis among all forty whole genome sequences available for cyanobacteria (3 thermophiles- Thermosynechococcus elongatus BP-1, Synechococcus sp. JA-2-3B'a (2-13), Synechococcus sp. JA-3-3Ab and 37 mesophiles) was performed to identify genomic and proteomic factors responsible for the behaviour of T. elongatus BP-1, a thermophilic unicellular cyanobacterium with optimum growth temperature [OGT] of 55°C. Majority of genomic and proteomic characteristics for this cyanobacterium indicated contrasting features indicating its mesophilic behaviour while the role of mutational biasness and selection pressure is thought to be responsible for high OGT. Contradictory results were obtained for T. elongatus for synonymous codon usage, CvP-bias and amino acid composition with respect to thermophilic behaviour. Calculated J2 index is lowest among all cyanobacterial genomes. Except for proline and termination codons, T. elongatus showed synonymous codon usage pattern which is expected for mesophiles. Results indicated that among cyanobacterial genomes, majority of genomic and proteomic determinants put T. elongatus very close to mesophiles and the whole genome of this organism represents continuous gain of mesophilic rather than thermophilic behavior.