Microorganisms have evolved through years by adapting their genomes to survive under specific conditions. Thermophiles are a group of microorganisms thriving under continuous stress and must adapt to environmental changes, incorporating novel genetic features and physiological capabilities to inhabit extreme environments. The transference of genetic material among distantly related phyla has been reported to play a major role in microbial evolution. In this study, we will present a couple of examples of thermophilic microorganisms with metabolic features apparently gained through horizontal gene transfer. These cases are Caldanerobacter subterraneus and Fervidobacterium spp. Three genomes of Caldanaerobacter subterraneus strains are available. These strains posses a gene cluster encoding carbon monoxide dehydrogenase and energy converting hydrogenase, which are key enzymes in the metabolism of CO utilization, that forms distinct clades as seen by phylogenetic reconstruction. Four genomes of Fervidobacterium species are available. In this genus, around 40 transposase genes were detected per genome. A large fraction of these transposase genes had as closest relatives sequences from different phyla suggesting the potential for active horizontal gene transfer events. The question on whether the transference of DNA between distantly related species is uni- or bi-directional remains to be answered. This study presents some evidences on the importance of horizontal gene transfer in thermophiles and analyzes if these transference events represent a process for the benefit of only some species or if it is a mechanism that microorganisms are looking for to all gain from the physical interaction and potential sharing of genetic material.

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