Physiology, Heavy Metal Resistance, and Genome Analysis of Two Strains Isolated from the Naica Mine (Mexico).

Here, we report the characterization of two strains, NOV2-1 and OV2-1, isolated from an iron-oxide deposit in an underground tunnel of the Naica mine in Mexico. This unique biotope, characterized by its high temperature (≈50 °C) and the presence of heavy metals, is no longer available for sampling at this time. The genomes of NOV2-1 and OV2-1 comprised two replicons: a chromosome of 3.58 and 3.53 Mb, respectively, and a chromid of 2.1 Mb in both strains. No plasmids were found. The average nucleotide identity and the core genome phylogeny showed that NOV2-1 and OV2-1 belonged to the species. NOV2-1 and OV2-1 grew up to 48 °C, with an optimal temperature of 42 °C. Discrete differences were observed between CCUG38401, NOV2-1, and OV2-1 in the biochemical tests. NOV2-1 and OV2-1 presented resistance to zinc, lead, copper, cadmium, nickel, and cobalt. Several complete and incomplete gene clusters related to the resistance to these heavy metals (, , 1, - 2, , , and ) were detected in the genome of these strains. Although further studies are needed to determine the origin and role of the detected gene clusters, it is suggested that the system may have been mobilized by horizontal gene transfer. This study expands the extreme biotopes where strains can be retrieved.