Effect of substrate composition on microbial diversity and efficiency of in situ pilot-scale passive sulfate-reducing bioreactors treating acid mine drainage

Acid mine drainage (AMD) is an environmental problem of a global scale. Passive remediation strategies utilizing the metabolism of sulfate-reducing bacteria have emerged as promising options for the mitigation of impacted AMD sites. In order to test the effect of varying complex and simple carbon sources on AMD remediation efficiency, pilot-scale bioreactors were constructed and exposed to AMD in situ over a ten-month period. Geochemical analyses suggested that the efficiency of AMD remediation depended more on the seasonal weather patterns of Southern Illinois, USA than the substrate composition of each bioreactor. Enrichment cultures targeting sulfate-reducing organisms yielded several isolates most closely related to members of the genera Desulfovibrio and Clostridium. Microbial community analysis was performed using fluorescent in situ hybridization, 16S rRNA gene targeted pyrosequencing, and quantitative polymerase chain reaction (qPCR). Results suggested that the depth from which samples were taken as well as the substrate composition impacted the microbial communities within each bioreactor. Over the course of the experiment the community changed from one similar to that of a bovine rumen to one more adapted to the acidic nature and high metal content of AMD. Community abundance based on 16S rRNA gene and dsrB gene copy number suggested an overall decrease in the bacterial population over the course of the study.