Microbial Sulfur and Arsenic Oxidation Facilitate the Establishment of Biocrusts during Reclamation of Degraded Mine Tailings

Degraded tailings generated by the mining of metal ores
are major
environmental threats to the surrounding ecosystems. Tailing reclamation,
however, is often impeded due to adverse environmental conditions,
with depleted key nutrients (i.e., nitrogen (N) and phosphorus (P))
and elevated sulfur and metal(loid) concentrations. Formation of biocrusts
may significantly accelerate nutrient accumulation and is therefore
an essential stage for tailing reclamation. Although suggested to
play an important role, the microbial community composition and key
metabolisms in biocrusts remain largely unknown and are therefore
investigated in the current study. The results suggested that sulfur
and arsenic oxidation are potential energy sources utilized by members
of predominant biocrust bacterial families, including Beijerinckiaceae, Burkholderiaceae, Hyphomicrobiaceae, and Rhizobiaceae. Accordingly, the S and As oxidation
potentials are elevated in biocrusts compared to those in their adjacent
tailings. Biocrust growth, as proxied by chlorophyll concentrations,
is enhanced in treatments supplemented with S and As. The elevated
biocrust growth might benefit from nutrient acquisition services (i.e.,
nitrogen fixation and phosphorus solubilization) fueled by microbial
sulfur and arsenic oxidation. The current study suggests that sulfur-
and arsenic-oxidizing microorganisms may play important ecological
roles in promoting biocrust formation and facilitating tailing reclamation.