Taxonomic shifts in bacterial communities of mine tailings suggest persistence of chemolithotrophic traits under oligotrophic and metal-rich conditions

Mine tailings, resulting from industrial processes, constitute extreme environments due to toxic heavy metals, metalloids, and low concentrations of inorganic nitrogen, phosphorus, and organic carbon. Despite these selective pressures, pioneer microorganisms colonize these substrates, utilize limited resources, alter environmental conditions, and initiate ecological succession. This study characterized the geochemical conditions of mine tailings across three deposition ages (0, 1.5, and 5 years) and compared bacterial community diversity between the 1.5- and 5-year-old tailings from Durango, Mexico, using the 0-year geochemical dataset as a physicochemical reference point. Environmental DNA was extracted from the tailings, and the V4-V5 region of the bacterial 16S rRNA gene was amplified and sequenced using a metabarcoding approach. No environmental DNA was recovered from recently deposited samples; however, 127 bacterial genera were identified across both mine tailings, with 47 genera shared. The 5-year-old tailings exhibited greater genus richness than the 1.5-year-old samples. Pseudomonadota phylum dominated both communities, followed by Actinomycetes . The chemolithoautotrophic genus Thiobacillus , capable of oxidizing sulfide, sulfur, and thiosulfate, was the most abundant. Chemolithoheterotrophic thiosulfate-oxidizing Limnobacter and Sulfurifustis were prevalent in young and old tailings, respectively. Chemoorganoheterotrophic bacteria, including Nocardioides and Kribella ( Actinobacteria ), as well as Hydrogenophaga and Pseudomonas ( Betaproteobacteria ), were also detected. The relative abundance of chemolithoautotrophic bacteria corresponded with the geochemical conditions of the mine tailings, which lack organic carbon and contain abundant reduced inorganic sulfur compounds as energy sources. In this exploratory study, early ecological succession at the bacterial genus level was evident, primarily involving Sulfurifustis , Nocardioides , and Kribella .