Microbial Population Dynamics and the Role of Sulfate Reducing Bacteria Genes in Stabilizing Pb, Zn, and Cd in the Terrestrial Subsurface

Milling and mining metal ores are major sources of toxic metals contamination. The Spring River and its tributaries in southeast Kansas are contaminated with Pb, Zn, and Cd because of 120 years of mining activities. Trace metal transformations and cycling in mine waste materials greatly influence their mobility and toxicity and they affect both plant productivity and human health. It has been hypothesized that under reduced conditions in sulfate-rich environments, these metals can be transformed into their sulfide forms, thus limiting mobility and toxicity. We studied biogeochemical transformations of Pb, Zn, and Cd in flooded subsurface mine waste materials, natural or treated with organic carbon (OC), and/or sulfur (S), by combining advanced microbiological and X-ray spectroscopic techniques to determine the effects of treatments on the microbial community structure and identify the dominant functional genes that are involved in the biogeochemical transformations, especially metal sulfide formation over time. Samples collected from medium-, and long-term submerged columns were used for microarray analysis via functional gene array (GeoChip 4.2). The total number of detected gene abundance decreased under long-term submergence, but major functional genes abundance was enhanced with OC-plus-S treatment. The microbial community exhibited a substantial change in structure in response to OC and S addition. Sulfate-reducing bacteria genes dsrA/B were identified as key players in metal sulfide formation via dissimilatory sulfate reduction. Uniqueness of this study is that microbial analyses presented here in detail are in agreement with molecular-scale synchrotron-based X-ray data, supporting that OC-plus-S treatment would be a promising strategy for reducing metal toxicity in mine waste materials in the subsurface environment