Microbial mechanisms of sulfate reduction for low-temperature bioremediation of acid-mined uranium sandstone groundwater

The bioremediation efforts using sulfate-reducing bacteria (SRB) face significant challenges due to prolonged start-up times and instability under extreme environmental conditions, such as the low temperatures and acidic groundwater found in uranium mining areas. To address the issues, cold-tolerant SRB inocula were selectively screened to efficiently remove sulfate and heavy metals from raw groundwater at 15 °C, achieving a high specific sulfate reduction rate of 2.3 gSO₄²⁻·gVSS⁻¹·d⁻¹. Enterobacteriaceae emerged as the most prevalent SRBs in inoculum, constituting 28 % of the total population. We further found that these SRB harbored diverse genes for cold and acidic adaptation, such as ompC and cspA encoding porin protein and cold shock protein, respectively, as well as F-type H⁺-transporting ATPase genes maintaining intracellular pH homeostasis in acidic environments. However, when scaling up from a lab-scale bioreactor (0.1 L) to a pilot-scale system (1000 L), the limited growth of Enterobacteriaceae led to a decrease in the sulfate reduction rate, which may result from the lack of biosynthesis pathways of alanine and tyrosine. Taken together, our results revealed the potential mechanisms of SRB for cold and acidic adaptation, which provides a theoretical foundation to develop in situ bioremediation for acid-mined uranium groundwater at low temperature.