Characterization of an enriched acidophilic sulfate-reducing bacteria community from the sediment of a uranium mine (Minas Gerais-Brazil).

Abstract

Acidophilic sulfate-reducing bacteria (SRB) are anaerobic microorganisms capable of precipitating metals and raising pH levels in acidic drainage waters. Limited genera have been isolated from acidic sediments. This study aimed to characterize enrichment cultures of acidophilic SRB communities found in uranium mine sediments in Minas Gerais, Brazil. Enrichment tests evaluated lactate and acetate as electron donors across various pH levels. Results revealed SRB growth in both carbon sources at pH 3, 4, and 5, with sulfate removal rates of approximately 98% for lactate and 97% for acetate. Notably, Desulfosporosinus was abundant (27%) in both carbon source assays. In the acetate experiment, Acidocella, an acidophilic acetoclastic microorganism, dominated (39%), alongside Desulfosporosinus (27%). The latter, typically exhibiting incomplete metabolism, might use hydrogen or other forms of extracellular electron transfer (EET), potentially including direct interspecies electron transfer (DIET), in syntrophy with Acidocella spp. The predominance of Desulfosporosinus spp. and Clostridium spp. in the enrichment cultures also suggests a cooperative metabolic network in which fermentative bacteria play a critical role in initiating sulfate reduction under acidic conditions. These findings underscore the efficacy of the native acidophilic SRB enrichment strategy, both in recovering indigenous strains and in generating a functionally effective inoculum for sulfidogenic bioreactor systems, operating at low pH. This approach holds promise for treating Acid Mine Drainage (AMD) and merits further scalable research.