Distinctive microbial communities linked with pH and heavy metals in mine drainages across all regions of Japan

Passive treatment using microorganisms is a promising method for removing toxic metals from acid mine drainage (AMD). To provide a better understanding of the compositions of mine microbial communities and their relationship with pH and metal concentrations in mine water, we analyzed both physicochemical data and 16S rRNA gene amplicon sequences from 40 untreated drainages from 30 abandoned mines across all regions of Japan. In the 40 mine drainages, higher concentrations of metals (iron, lead, cadmium, copper, and manganese) were detected in mine drainages with acidic pH (< 4.5; 24 samples) than in those with circumneutral pH (> 6.0; 16 samples), except for arsenic. Comparison of principal coordinate analysis scatter plots between mine drainages of acidic and circumneutral pH revealed a relatively clear separation of microbial compositions except for one mine drainage sample. In the 24 AMDs, the dominant operational taxonomic units (OTUs) found at relative abundance levels >3 % were generally one of three related to Caballeronia arationis, Ferrovum myxofaciens, or Gallionella capsiferriformans, except for two mine drainage samples. Although the microbial communities of the 40 mine drainages were obtained from a single sampling time (triplicate analysis), they may reflect the typical microbial communities of each mine drainage, because analysis of drainage samples taken from the same sampling point over three different seasons (summer, autumn, and winter) revealed similar communities regardless of the season. Among mine drainages analyzed in this study, the OTU showing 96.8 % identity to C. arationis was the most prevalent bacterial OTU, which was found in 23 drainages (the top OTU in 15 mine drainages) with >3 % relative abundance.