Selection of heavy metal tolerant extremophilic consortia from the volcanic area of Caviahue-Copahue

MASSELLO F.; DONATI E.R.

Congreso; SAMIGE 2019; 2018

Biomining and bioremediation are alternatives to the traditional chemical procedures for recovering metals and for the remediation of polluted sites, respectively. Microorganisms useful for such technologies are usually present in very extreme environments with high concentrations of heavy metals under acidic conditions. To survive in such conditions these extreme microorganisms had to develop different tolerance mechanisms. Certain volcanic areas as Caviahue-Copahue (Neuquén) are perfect environments for this kind of polyextremophilic microorganisms. Rio Agrio runs from the crater of Copahue volcano forming several cascades before and after Caviahue lake. A sample from a great cascade after the lake (Salto del Agrio) was taken and several enrichments were performed to select acidophilic iron/sulfur oxidizing microorganisms (using MAC medium), neutrophilic organotrophs (using LB medium), and anaerobic microorganisms (using modified Postgate medium). The maximum tolerant concentration was later assessed for five heavy metals (Cd, Cu, Ni, Zn, and Co) for each consortium obtained from the enrichments. Interestingly, the three consortia were tolerant to relatively high concentrations of each metal being the mean tolerances obtained: cadmium 30 mg.l-1, copper 71 mg.l-1, nickel 203 mg.l-1, zinc 553 mg.l-1, and cobalt 173 mg.l-1. These results confirm the widely reported observation that extremophilic microbial communities are naturally poly-tolerant even when some of the contaminants are not present at such high concentration. At the same time, tolerance was induced artificially through successive cultures in which the metal concentration was increased until no growth was measured. On this wise, we selected fifteen consortia (five acidophilic, five organotrophic, five anaerobic) tolerant to high concentrations of cadmium, copper, nickel, zinc or cobalt. Remarkably, some of them were tolerant to concentrations higher than the 75 % of those reported in literature for resistant microorganism and consortia suggesting they could be used in different processes for recovering or remediating metals. Acidophilic consortia were the most tolerant ones exhibiting tolerance to approximately 11 g.l-1 of cadmium, 0,6 g.l-1 of copper, 23 g.l-1 of nickel, 26 g.l-1 of zinc, and 12 mg.l-1 of cobalt. Some preliminary results on the phylogeny of the microorganisms present in the different consortia are also included in this communication.