Sulfadiazine degrading bacteria Vibrio alginolyticus isolated from mariculture wastewater: Performance, degradation pathways, and mechanisms based on transcriptomic analysis

In this study, two strains of novel sulfadiazine (SDZ)-degrading bacteria Vibrio alginolyticus SUL-3 and SUL-5 were isolated from the SDZ contaminated mariculture wastewater. The degradation rate of two strains reached 54.11% ± 0.15% and 63.57% ±0.07% of 1 mg/L SDZ within 4 d, respectively, and could also degrade other 3 sulfonamides (sulfamethoxazole, sulfamonomethoxine, and sulfamethazine). Optimal degradation conditions were identified as: neutral pH (7.0), marine salinity (35‰), and temperature of 30 °C. The addition of exogenous carbon and nitrogen sources was found to enhance bacterial degradation of SDZ at a concentration of 10 mg/L. However, this stimulatory effect was either insignificant or even inhibitory at lower SDZ concentrations. Through bond cleavage, hydroxylation and ring opening, 12 SDZ biodegrading intermediates were verified, showing less toxic than their parent. Multidrug resistance genes were identified in SUL-5 through whole-genome analysis, including sulfonamide resistance gene sul2 , which was the most prevalent sulfonamide resistance determinant in aquatic environments. Comparing differentially expressed genes (DEGs) between groups with or without SDZ, oxidoreductases, transferases, hydrolases, and lyases were proved to participate in the biodegradation of SDZ. SUL-5 adapted to and degraded SDZ by upregulating genes encoding ATP-binding cassette (ABC) transporters, degradation-related, and multidrug efflux pump enzymes. This research provides insights into the survival and biodegradation mechanisms of Vibrio sp. and evaluates its potential for environmental bioremediation.