Insight into adaptation mechanisms of marine bacterioplankton from comparative genomic analysis of the genus Pseudohongiella

Five novel Pseudohongiella strains were isolated from 400 to 450 m water depths in the South China Sea. The 16S rRNA gene sequences of these isolates, as well as their relatives, were analyzed by the All-Species Living Tree LTPs123, indicating that those Pseudohongiella strains should be phylogenetically classified into the family Alcanivoraceae. Notably, the cultivation-independent results showed that Alcanivoraceae bacteria exhibited enormous quantitative dominance at 450 m. To understand their adaptation mechanisms, the genomes of two representatives (strains SCS-49^T and SCS-111) were sequenced and annotated. Comparative genomic analysis among the strains SCS-49^T, SCS-111 and other Pseudohongiella strains suggested that the SCS strains might adapt to pelagic environments by integrating foreign DNA into their genomes through horizontal gene transfer, which might enhance their abilities in transportation, the metabolism of certain substrates, and responses to external changes.