Biochemical and molecular mechanisms of resilience in the response of prokaryotes of an active volcano to cadmium-induced stress.

The crater lake of the active volcano "El Chichón" in Mexico, represents an ecosystem characterized by changing conditions of salinity, acidity, temperature, and the concentration of different heavy metals, posing significant challenges to the abundance and diversity of microorganisms. In this study, anaerobic mesophilic and hyperthermophilic prokaryotic microbiomes isolated from the volcano-lake were evaluated to elucidate the molecular and biochemical mechanisms involved in Cd2+ bioremoval. Cultures consumed actively carbohydrates, triacetylglycerol, acetate and methanol; the hyperthermophilic microbiome produced 50% more biomass than mesophiles at the end of the growth curve; however, the presence of Cd2+ stimulated the biomass and methane production in the mesophilic microbiome. The relative abundance of the 16S rRNA metabarcoding analysis showed dominance of Firmicutes and Euryarchaeota in both microbiomes. The constitutive synthesis of biofilm and the overproduction of polyphosphates and thiol group molecules were protection mechanisms against Cd2+ toxicity. Such mechanisms allowed 68-74% of Cd2+ bioremoval (biosorption plus accumulation) at concentrations up to 500 µM CdCl2. Data suggested that the prokaryotic microbiome isolated from the extreme environment of the "El Chichón" volcano is forming a complex metabolic resilient network involving methanogenesis with phosphate and sulfur metabolism that is capable of thriving under extreme conditions of pH, temperature, and the ability for the Cd2+ removal. This work provides for the first time, information on the mechanisms of tolerance to poly-extreme conditions; moreover, microbiomes studied here may be a promising strategy for biotechnological applications under extreme conditions.