Anaerobic biodegradation of four sulfanilamide antibiotics: Kinetics, pathways and microbiological studies

Large amounts of sulfanilamide antibiotics (SAs) have been excreted into the manure. In this study, the anaerobic biodegradation of four kinds of SAs including sulfaquinoxaline (SQX), sulfamethoxazole (SMX), sulfamethoxine (SMD) and sulfathiazole (STZ) was investigated. The degradation rates of SQX and STZ decreased with the increase of the concentrations of other organics, but those of SMX and SMD were less affected. The average degradation rates of SAs were in the order of SMX >SMD ≈QX >STZ, with the best degradation rate constants of 0.30125, 0.14752, 0.16696, and 0.06577 /d, respectively. STZ had the greatest effect on the population richness of microbes, whereas SQX had the largest impact on the population diversity. The degradation rates of SAs were positively correlated with the abundances of Proteobacteria and Bacteroidetes, and negatively correlated with the abundance of Firmicutes. The common degradation pathways of SAs were S-N cleavage and substitution. The specific functional groups of SQX, SMX and SMD, including quinoxaline, isoxazole and pyrimidine rings, could be opened, but the thiazole ring of STZ was difficult to be decomposed. After the rings of the specific functional groups were opened, they would be further substituted or decomposed to be products with small molecules.