Interspecific Electron Transfer-Driven Oxytetracycline Degradation by Autotrophic Coculture of Sulfur-Oxidizing and Sulfate-Reducing Bacteria

Interspecific electron transport (IET) can promote the cometabolism of microorganisms, so it is of great significance in environmental remediation. Herein, a coculture of autotrophic sulfur-oxidizing bacteria (SOB) and heterotrophic sulfate-reducing bacteria (SRB) was constructed to biodegrade oxytetracycline (OTC) (upgraded to 120.9 ± 3.9 μg mg–1 protein d–1) under inorganic conditions, and the biodegradation was markedly improved (1.5 times) after loading biosynthetic FeS (bio-FeS). The increase of the NAD+/NADH ratio and ATPase activity indicated that more electrons generated by intracellular metabolism inside the SOB (lacking the OTC enzyme) outflowed extracellularly to the SRB via the IET chain in the coculture system. Linear sweep voltammetry (LSV) and I–t analysis indicated that bio-FeS on the SRB could enhance direct interspecific electron transport (DIET) mainly via c-Cyts, together with the mediated interspecific electron transport (MIET) via flavins, thus accelerating the OTC efflux. Community analysis demonstrated that the SRB introduction increased the abundance of genes related to environmental information, cell motility, membrane transport, and signal transduction in the coculture system. This discovery revealed the feasibility of antibiotic degradation using heterotrophic bacteria (such as SRB) under inorganic conditions and deepened the understanding of the antibiotic degradation in biogeochemical cycles involving carbon, nitrogen, and sulfur in natural ecosystems.