Viruses of the Thermotogota; the vehicles on the highways of gene sharing

Abstract Viruses are drivers of microbial ecology and evolution controlling populations and disseminating DNA laterally among the cells they infect. Phylogenetic and comparative genomic analyses of Thermotogota bacteria have shown high levels of lateral gene transfer with distantly related organisms, particularly with Firmicutes. One likely source of such DNA transfers is viruses, however, to date only three temperate viruses infecting Marinitoga bacteria have been characterized in this phylum. Here we use a bioinformatic approach to identify an additional 17 proviruses integrated into genomes of eight Thermotogota genera including Marinitoga. We also induce viral particle production from one of the newly identified proviruses. The proviruses fall into two groups based on sequence similarities, gene synteny and virus classification tools. Group-1 shows similar genome structure to the three previously identified Marinitoga viruses while Group-2 are distantly related to these viruses and have different genome organization. Both groups show close connections to Firmicutes in genomic- and phylogenetic analyses, and the Group-2 viruses show evidence of very recent transfer between these lineages and are likely capable of infecting cells from both phyla. We suggest that viruses are responsible for a large portion of the laterally transferred DNA between these distantly related lineages.