Culture/Co-Culture Dependent and Independent Identification of Bacterial Communities along a Chronosequence of Spontaneous Reclamation on Gold Mine Spoils in Peru

Abstract

Cyanide leaching is currently the dominant process used by the mineral industry to extract gold and silver minerals. Cyanide is a nitrogen compound toxic for most living organisms. Many microorganisms are able to tolerate and degrade cyanide and its derivatives. In this study, were considered bacteria from soil and water samples corresponding to a chronological sequence (up to 5 years) of spontaneous cyanide bioremediation in a gold mining area (La Libertad Region, Peru). Culture dependent molecular identifications, based on 16S rDNA amplification and sequencing, were performed for bacteria isolated on agar media. Co-culture dependent molecular identifications were performed through 16S rDNA targeted metagenomics based on Next generation Sequencing with DNA directly extracted from the co-cultures in order to determine bacteria species unable to grow individually on agar media. Culture independent identifications were similarly performed through 16S rDNA targeted metagenomics from DNA directly extracted from water or soil samples in order to establish their respective global microbiota. Concerning cyanide contaminated soils, more than one hundred operational taxonomic units (OTU) were identified by metagenomics with only 30% species co-cultivable in broth medium and 82 isolated strains, in particularPseudomonasspp. The global microbiota in non-contaminated soils was markedly different. Concerning cyanide contaminated waters, about one hundred operational taxonomic units (OTU) were identified by metagenomics with only 30% species co-cultivable in broth medium. The most frequently identified species belong toAlcaligenes, Alkalibacterium, Bacillus, PaenibacillusandSerratia. Bacteria isolated and co-cultivated from contaminated waters and soils are currently analyzed as candidates for cyanide bioremediation.