Arsenic tolerance and presence of specific resistance genes in heterotrophic consortia obtained from Copahue geothermal system.

DONATI E.R.; URBIETA M.S.; LIMA A.

Congreso; SAMIGE; 2017

The major sources of arsenic (As) pollution are related to anthropogenic intervention. Thiscarcinogenic metalloid can be found mainly in two oxidizing states: As(III) and As(V), being the first themost toxic form. Fortunately some microorganisms are able to metabolize arsenic contaminantsthrough several specific enzymes and proteins contributing to remediate polluted sites. The presentwork describes the influence of As on microbial growth and the presence of a variety of genes relatedto As metabolism and As resistance in two heterotrophic consortia obtained from a sample collectedfrom Caviahue-Copahue geothermal system (Salto del Agrio) and enriched in LB medium at 30°Csupplemented with increasing concentrations of NaAsO2 or Na2HAsO4.7 H2O. The consortia provedto be able to adapt to concentrations up to 20 mM of As(III) (culture called Het(As+3 20 mM)) and 450mM of As(V) (culture called Het(As+5 450 mM)). The phylogenetic analysis indicated the prevalence ofPaenibacillus profundus in both cultures. Control cultures, without As added, were carried out tocompare growth profiles ((As+3 0 mM) and (As+5 0 mM)). Growth was measured by OD600 every 24hours. After 4 days of incubation, Het(As+5 450 mM) reached their maximum OD600 meanwhileHet(As+5 0 mM) did that after 3 days; Het(As+3 20 mM) reached their maximum OD600 after 8 daysinstead of 2 days for Het(As+3 0 mM. Due to the lower toxicity of As(V), its influence on growth ofHet(As+5 450 mM) was less than As(III) on Het(As+3 20 mM). The growth profiles also showed thatthe cultures supplemented with As had longer lag phases than the controls without As, although finalconcentration of cells was similar in both. The screening of As resistance genes was done using 12primer sets. Interestingly, Het(As+3 20 mM) showed positive amplifications with 6 primers setcorresponding to two types of arrA genes that coded for a respiratory arsenate reductase, the acr3gen that coded for an arsenite transporter, two types of aioA genes that coded for an arsenite oxidaseand the arsC gen that coded for a cytoplasmic arsenate reductase. Curiously, the culture Het(As+5450mM) did not amplify with any of the primers assayed in spite of a great optimization effort. Ourstudy opens the door for the study of many diverse aspects of As tolerant microorganisms, from thegenetic resistant characteristics to the potential use in the remediation of contaminated sites.