Metagenomic and transcriptome elucidating the sulfamethoxazole degradation and metabolism pathways in fermentative bacteria and microalgae coupling system for mariculture wastewater treatment

Acidogenic fermentation coupled with microalgae cultivation is cost-effective for treating mariculture wastewater (MW), however the molecular responses of fermentative bacteria and microalgae to antibiotic in MW at the metagenomic and transcriptome levels remain unclear. In this study, the degradation process of sulfamethoxazole (SMX) and its effects on microbial metabolism pathways were investigated in a bacterial-algal coupling reactor (BACR). The SMX degradation efficiency reached to 73.5%, and the toxic impacts was reduced. The algal cell density analyzed with flow cytometer was improved by 72.8% under SMX stress. Higher superoxide dismutase activity and the accumulation of carbohydrate (40.2%), protein (36.8%), lipid (33.7%) reflected the intracellular responses of microalgae. Transcriptome analysis disclosed upregulation of photosynthesis, electron transport, ATP and DNA synthesis in response to SMX, thus promoting microalgae biomass accumulation. In fermentation unit, Proteobacteria and Bacteroidota as dominant functional microorganisms were enriched. Metagenomic analysis revealed that the abundance of carbon metabolism pathways and two-component signal transduction pathways increased by 32.3% and 82.9%, thus improved the adaptability of microbial community to antibiotic stress. The establishment of the fermentative bacteria and microalgae coupling system enhanced the biodegradability and promoted the tolerance to antibiotics stress.