Isolation and Identification of Arsenic-Resistant Extremophilic Bacteria from the Crater-Lake Volcano "El Chichon", Mexico.

The crater lake at "El Chichón" volcano is an extreme acid-thermal environment with high concentrations of heavy metals. In this study, two bacterial strains with the ability to resist high concentrations of arsenic (As) were isolated from water samples from the crater lake. Staphylococcus ARSC1-P and Stenotrophomonas ARSC2-V isolates were identified by use of the 16S rDNA gene. Staphylococcus ARSC1-P was able to grow in 400 mM of arsenate [As(V)] under oxic and anoxic conditions. The IC values were 36 and 382 mM for oxic and anoxic conditions, respectively. For its part, Stenotrophomonas ARSC2-V showed IC values of 110 mM and 2.15 for As(V) and arsenite [As(III)], respectively. Arsenic accumulated intracellularly in both species [11-25 nmol As × mg cellular prot in cells cultured in 50 mM As(V)]. The present study shows evidence of microbes that can potentially be a resource for the bio-treatment of arsenic in contaminated sites, which highlights the importance of the "El Chichón" volcano as a source of bacterial strains that are adaptable to extreme conditions.