In search of sulfate-reducing consortia able to degrade acetate under acidic conditions

BACKGROUND: Sulfate-reducing microorganisms (SRM) can help to remediate acidic effluents containing metals. One drawback of sulfate reduction is that some SRM do not completely oxidize the substrate to CO₂ and acetic acid may remain as a byproduct, affecting the process efficiency. Acidic environments are a potential source of sulfate-reducers able to thrive in acidic conditions. This work aimed to develop cultivable consortia of sulfate-reducing microorganisms able to consume acetate at acidic pHs and analyze their community composition. RESULTS: Starting from sediment enrichments from a natural acidic source, by successive transfers and combinations of electron donors and pHs we obtained seven sulfate-reducing consortia. All of the consortia consumed the acetate produced from the incomplete oxidation of the substrate (lactate or glycerol) and used 53–75% of the reducing equivalents for sulfate reduction. The sulfide production rate of the consortia was between 0.22 and 0.26 mmol L⁻¹ day^–1 in the pH range 3–6, being slightly higher at acidic conditions (pH 4–5). The microbial diversity of the consortia was dominated by 21 operational taxonomic units, including taxa of acetotrophic sulfate reducers (i.e. Desulfotomaculum and Desulfatirhabdium) and fermenting bacteria. CONCLUSION: The consortia reported here have the potential to serve as inoculum for sulfate-reducing bioreactors and could help to overcome acetate accumulation at low pHs.