Transcriptomics of Planococcus kocurii O516 reveals the degrading metabolism of sulfamethoxazole in marine aquaculture wastewater.

Environmental threat induced by residual antibiotics in marine aquaculture wastewater is an urgent problem to be solved. In this study, one sulfamethoxazole (SMX)-degrading bacterium, Planococcus kocurii O516 was isolated from high SMX marine aquafarm. The isolate was able to consume more than 60% of SMX with the initial concentration of 10 mg L-1 within 72 h. Transcriptome analysis found great gene expression differences in the strains with or without SMX dosage. Three putatively differentially expressed proteins, namely AbrB/MazE/SpoVT family DNA-binding domain-containing protein, pantoate-beta-alanine ligase and MerR family transcriptional regulator, were annotated in detail. They were inferred to trigger the strain's response to SMX stress. Reverse transcription-quantitative PCR (RT-qPCR) analysis of four significantly different expressed genes accorded well with expression changes revealed by transcriptomics and confirmed the validity of transcriptome analysis. According to functional annotations of the proteins obtained by transcriptome sequencing and structural analysis of the intermediate metabolites by GC-MS, a possible SMX degradation pathway was reasonably proposed. SMX was first decomposed into sulfonamide and 5-methylisoxazole. The sulfonamide was then hydroxylated to form 4-(hydroxyamino) benzenesulfonamide. Subsequently, the sulfamic acid was detached, and 4-(hydroxyamino) phenol was formed. Finally, 4-aminophenol was generated from dehydroxylated of 4-(hydroxyamino) phenol. In sum, transcriptome analysis of the P. kocurii in response to SMX stress benefits to revealing the degradation pathway of SMX and will provide theoretical feasibility for the application of microbial method to treat the SMX-contaminated aquaculture wastewater.