Phyletic patterns of bacterial growth temperature in and reveal gradual and sporadic evolution towards cold adaptation.

Bacterial species adapt to cold environments with diverse molecular mechanisms enabling their growth under low ambient temperature. The emergence of cold-adapted species at macro-evolutionary scale, however, has not been systematically explored. In this study, we performed phylogenetic analysis on the growth temperature traits in the genera that occupy broad environmental and host niches and contain known cold-adapted species. Our results demonstrate that in the genus , cold-adapted species formed a distinct and conserved clade, whereas in , cold-adapted species were sporadically distributed throughout the phylogenetic tree. The cold-adapted clade of exhibited genome-wide signatures of adaptation and possessed clade-specific genes. This indicates that there are diverse evolutionary patterns in the divergence of cold-adapted species among different bacterial genera.