Optimal growth temperature of prokaryotes correlates with class II amino acid composition.

Partitioning of aminoacyl-tRNA synthetases and their associated amino acids into two classes allows us to distinguish between thermophilic and mesophilic species based only on amino acids composition. The CLASSDB program has been developed for amino acid content analysis in organisms treated individually or pooled together to form a pattern of characteristic properties. A strong correlation has been observed between optimal growth temperature (OGT) of organisms and class II amino acids content. Amino acid composition in organisms closely related phylogenetically but dissimilar in their OGT testifies that thermo-adaptation happens rather rapidly on the time scale of evolution.