Unveiling the environmental fate and risks of non-heterocyclic sulfacetamide: From a novel degradation mechanism to microecological effects.

The presence of sulfonamides (SAs) in the environment has been demonstrated to be a significant factor in pollution. Despite extensive research on heterocyclic SAs, the degradation mechanisms and ecological effects of non-heterocyclic sulfacetamide (SA) remain poorly understood. Our previous study isolated a challenging-to-culture strain, Leucobacter sp. HA-1, known for its SAs-degrading capacity, contains the conserved gene sadA. However, SA was not detected within the degradation spectrum linked to monooxygenase SadA activity. This indicates that other genes may be involved in SA degradation in strain HA-1. In this study, two adjacent and functionally similar amidohydrolases, SamA1 and SamA2, were identified from strain HA-1 as initiators of SA degradation to sulfanilamide (SN). The amino acid sequence similarities of SamA1 and SamA2 with reported enzymes were 39.44% and 34.54%, respectively. The combined expression of SamA1 and SmaA2 had a synergistic effect in enhancing the degradation and resistance of SA. The molecular mechanism behind strain HA-1's SA degradation was elucidated through microscopic analysis combining enzyme characterization with toxicological assessments and comparative genomics. An artificial bioremediation microecosystem targeting SA was established, notably, adding HA-1 enhanced bioaugmentation efficacy for SA elimination significantly. Metagenomic analyses revealed dynamic changes in antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and potential functional enzymes related to SA biodegradation within these microecosystems. Under our experimental conditions, bioaugmentation with HA-1 showed potential as a strategy for SA removal and reduced the accumulation or spread risk of ARGs and MGEs. This study revealed the fate mechanisms and microecological effects of non-heterocyclic sulfacetamide SA, which are different from typical SAs, and contributes to the further promotion of the elimination of the negative environmental and ecological impacts of antibiotics.