The Potential Role of Halothiobacillus spp. in Sulfur Oxidation and Acid Generation in Circum-Neutral Mine Tailings Reservoirs

Abstract

The biogeochemistry of acid mine drainage (AMD) derived from waste rock associated sulfide mineral oxidation is relatively well-characterized and linked to <i>Acidithiobacillus</i> spp.. However, little is understood about the microbial communities and sulfur cycling before AMD develops, a key component of its prevention. This study aimed to examine circum-neutral mining impacted water (MIW) communities and its laboratory enrichments for sulfur oxidizing bacteria (SoxBac). MIW <i>in situ</i> microbial communities differed in diversity, structure and relative abundance consistent with site specific variations in total aqueous sulfur concentrations (TotS; ~2-17 mM), pH (3.67-7.34), and oxygen (22-93% saturation). However, the sulfur oxidizer, <i>Halothiobacillus</i> spp. dominated seven of the nine total SoxBac enrichment communities (~76-100% relative abundance), spanning three of the four mines. The presence and relative abundance of the identified sixteen known and five unclassified <i>Halothiobacillus</i> spp. here, were the important clustering determinants across parent MIW and enrichment communities. Further, the presence of <i>Halothiobacillus</i> spp. was associated with driving the pH <4 in enrichment experiments, and the combination of specific <i>Halothiobacillus</i> spp. in the enrichments affected the observed acid to sulfate ratios indicating differential sulfur cycling. <i>Halothiobacillus</i> spp. also dominated the parent communities of the two acidic MIWs providing corroborating evidence for its active role in net acid generation within these waters. These results identify a putative indicator organism specific to mine tailings reservoirs and highlight the need for further study of tailings associated sulfur cycling for better mine management and environmental stewardship.