New Perspectives on the Mechanisms Underlying the Biodegradation of Sulfadiazine-Contaminated Substrates by Hermetia Illucens

The growing discharge of antibiotic residues into the natural environment, stemming from both human activities and animal farming, has increasingly detrimental effects on natural ecosystems and serves as a significant driving force for the spread of antibiotic resistance. Biodegradation is the substantial method for the elimination of antibiotics from the contaminated substrates, but the authentication of in situ degrader populations remains a formidable task. Here, DNA stable isotope probing (DNA-SIP) was employed to identify active sulfadiazine (SDZ) degraders involved in the biodegradation of SDZ among the gut microbes of black soldier fly larvae (BSFLs). The highest degradation efficiency with an initial SDZ concentration of 100 mg kg-1 reached 73.99% after 6 days at 28 °C. DNA-SIP revealed the incorporation of 13C6-labeled SDZ into 9 genera, namely, Clostridum sensu stricto 1, Nesterenkonia, Bacillus, Halomonas, Dysgonomonas, Caldalkalibacillus, g_unclassified_f_Xanthomonadaceae, g_unclassified_f_Micrococcaceae and Enterococcus. Co-occurrence network analysis revealed that there may exist synergistic interactions among the SDZ degraders in the gut microbiota, such as between Clostridium sensu stricto 1 and Nesterenkonia, which are the most abundant components of sulfonamide-degrading bacterial communities in sediment according to previous literature. In terms of function prediction, the significant increase in the KEGG level 2 pathways carbohydrate metabolism, membrane transport and translation as well as the significant enrichment of unique KOs related to the metabolism of ATP, the PTS system, saccharides and transcription played a crucial role during the biodegradation of SDZ in the BSFL gut. The results contributed to illustrating the structure of SDZ-degrading microbes in the BSFL gut and the degradation mechanisms in situ.