Evidence of horizontal gene transfer by transposase gene analyses in Fervidobacterium species

Horizontal Gene Transfer (HGT) plays an important role in the physiology and evolution of microorganisms above all thermophilic prokaryotes. Some members of the Phylum Thermotogae (i.e., Thermotoga spp.) have been reported to present genomes constituted by a mosaic of genes from a variety of origins. This study presents a novel approach to search on the potential plasticity of Fervidobacterium genomes using putative transposase-encoding genes as the target of analysis. Transposases are key proteins involved in genomic DNA rearrangements. A comprehensive comparative analysis, including phylogeny, non-metric multidimensional scaling analysis of tetranucleotide frequencies, repetitive flanking sequences and divergence estimates, was performed on the transposase genes detected in four Fervidobacterium genomes: F. nodosum, F. pennivorans, F. islandicum and a new isolate (Fervidobacterium sp. FC2004). Transposase sequences were classified in different groups by their degree of similarity. The different methods used in this study pointed that over half of the transposase genes represented putative HGT events with closest relative sequences within the phylum Firmicutes, being Caldicellulosiruptor the genus showing highest gene sequence proximity. These results confirmed a direct evolutionary relationship through HGT between specific Fervidobacterium species and thermophilic Firmicutes leading to potential gene sequence and functionality sharing to thrive under similar environmental conditions. Transposase-encoding genes represent suitable targets to approach the plasticity and potential mosaicism of bacterial genomes.