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The availability of genome sequences of Thermotogales species from across the order allows an examination of the evolutionary origins of phenotypic characteristics in this lineage. Several studies have shown that the Thermotogales have acquired large numbers of genes from distantly related lineages, particularly Firmicutes and Archaea. Here, we report the finding that some Thermotogales acquired the ability to synthesize vitamin B12 by acquiring the requisite genes from these distant lineages. Thermosipho species, uniquely among the Thermotogales, contain genes that encode the means to synthesize vitamin B12 de novo from glutamate. These genes are split into two gene clusters: the corrinoid synthesis gene cluster, that is unique to the Thermosipho and the cobinamide salvage gene cluster. The corrinoid synthesis cluster was acquired from the Firmicutes lineage, whereas the salvage pathway is an amalgam of bacteria- and archaea-derived proteins. The cobinamide salvage gene cluster has a patchy distribution among Thermotogales species, and ancestral state reconstruction suggests that this pathway was present in the common Thermotogales ancestor. We show that Thermosipho africanus can grow in the absence of vitamin B12, so its de novo pathway is functional. We detected vitamin B12 in the extracts of T. africanus cells to verify the synthetic pathway. Genes in T. africanus with apparent B12 riboswitches were found to be down-regulated in the presence of vitamin B12 consistent with their roles in B12 synthesis and cobinamide salvage. [ABSTRACT FROM AUTHOR]

Here we describe the genome of Mesotoga prima MesG1.Ag4.2, the first genome of a mesophilic Thermotogales bacterium. Mesotoga prima was isolated from a polychlorinated biphenyl (PCB)-dechlorinating enrichment culture from Baltimore Harbor sediments. Its 2.97 Mb genome is considerably larger than any previously sequenced Thermotogales genomes, which range between 1.86 and 2.30 Mb. This larger size is due to both higher numbers of protein-coding genes and larger intergenic regions. In particular, the M. prima genome contains more genes for proteins involved in regulatory functions, for instance those involved in regulation of transcription. Together with its closest relative, Kosmotoga olearia, it also encodes different types of proteins involved in environmental and cell–cell interactions as compared with other Thermotogales bacteria. Amino acid composition analysis of M. prima proteins implies that this lineage has inhabited low-temperature environments for a long time. A large fraction of the M. prima genome has been acquired by lateral gene transfer (LGT): a DarkHorse analysis suggests that 766 (32%) of predicted protein-coding genes have been involved in LGT after Mesotoga diverged from the other Thermotogales lineages. A notable example of a lineage-specific LGT event is a reductive dehalogenase gene—a key enzyme in dehalorespiration, indicating M. prima may have a more active role in PCB dechlorination than was previously assumed. [ABSTRACT FROM AUTHOR]