Effects of sulfamethoxazole on nitrogen transformation and antibiotic resistance genes in short-cut nitrification and denitrification process treating mariculture wastewater

The influential mechanism of sulfamethoxazole (SMX) on short-cut nitrification and denitrification (SCND) and antibiotic resistance genes (ARGs) was evaluated in a sequencing batch reactor (SBR). Excellent removal for NH4+-N and total inorganic nitrogen (TIN) was realized with above 95.7 and 93.0 % under 0.0-1.2 mg/L SMX, while 2.0 mg/L SMX induced the deterioration of their removal to 53.5 and 55.2 %, respectively. SMX altered the microbial composition by showing positive correlation to microbes, resulting in the dominant microorganisms changing from Denitromonas to Vibrio and occurrence of more antibiotic resistance bacteria (ARB). SMX dosage suppressed significantly ammonia oxidizing bacteria (AOB) Nitrosomonas, but enriched and diversified the denitrifying bacteria (DNB). 2.0 mg/L SMX led to the emergence of heterotrophic nitrification-aerobic denitri-fication (HNAD) as a nitrogen removal pathway and strengthened the sulfide-oxidizing autotrophic denitrifi-cation (SOAD) process by enrichment of SOAD bacteria (Candidatus_Thiobios, Sedimenticola). Metagenomic analysis revealed that 2.0 mg/L SMX decreased the NH4+-N removal by reducing nitrification related genes (amoABC, hao) at genetic level. Compared with 0.0 mg/L SMX, 2.0 mg/L SMX significantly inhibited the electron supply for heterotrophic denitrifying process by restraining the carbon source metabolism related genes (such as ACSS, sucC, mdh), but stimulated the electron generation for autotrophic denitrification by enhancing sulfide oxidation related genes aprA and aprB. Moreover, 2.0 mg/L SMX induced higher diversity and relative per-centage of antibiotic resistance genes (ARGs) but barely affected the potential ability of dissemination of ARGs, revealing SCND was a promising system for controlling transmission of ARGs under SMX treating mariculture wastewater.

Automated summary

The influence of sulfamethoxazole (SMX) on short-cut nitrification and denitrification (SCND) and antibiotic resistance genes (ARGs) was evaluated in a sequencing batch reactor (SBR). SMX dosage significantly affected the removal efficiency of NH4+-N and total inorganic nitrogen (TIN). The presence of SMX altered the microbial composition, leading to changes in dominant microorganisms and an increase in antibiotic resistance bacteria (ARB). 2.0 mg/L SMX induced the emergence of alternative nitrogen removal pathways and influenced the expression of nitrification and carbon source metabolism related genes, as well as the diversity and relative percentage of ARGs.