Bioleaching of heavy metals and removal of antibiotic resistance genes from sludge by diverse functional microbial consortia

Sewage sludge often contains heavy metals and antibiotic resistance genes (ARGs), posing challenges for its safe disposal. Bioleaching is a promising technique for heavy metal removal, but its impact on antibiotic resistance genes (ARGs), particularly when mediated by diverse consortia, remains unclear. This study systematically compared the efficiency of different functional microbial consortia, including Acidithiobacillus ferrooxidans (A. ferrooxidans), Acidithiobacillus thiooxidans (A. thiooxidans), and their combinations with the acid-tolerant yeast Rhodotorula mucilaginosa (R. mucilaginosa), for simultaneous bioleaching of heavy metals and removal of ARGs from sewage sludge. Results showed that the tripartite consortium (A. ferrooxidans + A. thiooxidans + R. mucilaginosa) achieved the highest removal efficiencies for copper (85.77%), arsenic (77.19%), and lead (70.88%). ARGs abundance generally decreased after bioleaching, with consortia containing A. ferrooxidans being most effective. A significant positive correlation was found between the reduction in Proteobacteria and the decrease in multiple ARGs. Interestingly, positive correlations were also observed between several heavy metals (Cr, Cu, Ni, As, Zn) and specific ARGs (IreK, macB, mlaF), indicating a complex interplay. This study highlights the importance of microbial synergy and heavy metal speciation in the co-control of heavy metals and ARGs in sewage sludge, providing insights for developing strategies for harmless treatment of sludge.