Deciphering the effects of sulfonamide antibiotics on denitrification from a metagenomic perspective: Inhibition of nitrite reduction and succession patterns of functional microorganisms.

Limited research has thoroughly elucidated the impact mechanisms of antibiotics on the denitrification process at the genomic and gene levels, which has hindered the optimization and development of nitrogen removal technology for antibiotic-containing swine wastewater. Lab-scale sequencing batch reactors were constructed in this study to treat synthetic wastewater containing different sulfonamides and nitrate. Investigations were carried out on denitrification performance, microbial community diversity, denitrifier succession patterns, and functional gene distribution. The stress of sulfonamides inhibited the nitrite reduction process, transforming complete denitrification into partial denitrification and causing significant nitrite accumulation. The average nitrogen removal efficiency in the treatment groups decreased from 81.0% ± 2.2-40.1% ± 6.1%. Alicycliphilus and Thauera were identified as the key taxa, accounting for 32.2% and 16.9% of all potential denitrifying bacteria, respectively. Although metagenome-assembled genomes (MAGs) from Thauera were enriched with genes encoding nitrate reductases (nap, nar) and nitrite reductases (nir), this genus preferentially utilized nitrate as an electron acceptor, resulting in the preferential nitrate reduction and subsequent nitrite accumulation. In contrast, Alicycliphilus MAGs developed tolerance to the sulfonamides stress during later stages, with concomitant enrichment of associated functional genes. They replaced Thauera to reemerge as the dominant group, thereby restoring complete denitrification. This study provides new insights into the regulatory mechanisms governing complete versus partial denitrification in nitrogen removal from antibiotic-containing wastewater.