Abstract:[Objective] The biodegradation of sulfur-containing amino acids is an important factor in the rise of toxic sulfides in the mariculture environment, and the analysis of the mechanisms and influencing factors of microbial degradation of sulfur-containing amino acids is a key link to control the sulfide concentration in this system. [Methods] This study used the dilution coating-stacked dish clamp method to isolate a sulfide-producing anaerobic strain from the sediment of the mariculture environment in this laboratory, and the mechanism and pathway of sulfide production with cysteine as substrate were investigated by metabolomics. [Results] The strain was identified as Citrobacter freundii, which reduced sulfate under anaerobic conditions and degraded cysteine to produce sulfide. The addition of l-cysteine improved its ability to reduce sulfate. The maximum accumulation of sulfide in this strain was 302.4 mg/L at 35 ℃, salinity 10, and pH 8.0 with 1 g/L l-cysteine as substrate. The study of cysteine desulfhydrase, the important contributor to sulfide production in the strain, revealed that the optimum temperature of this enzyme was 35 ℃, and it had high activity at pH 6.0-8.0, which could rapidly degrade cysteine to produce sulfide. Combined with the metabolomics study, it was found that the strain contained 3-mercaptopyruvate sulfotransferase, cystathionine gamma-lyase, and cysteine desulfhydrase catalyzing the degradation of cysteine was the main pathway to produce hydrogen sulfide, and sulfite reductase reducing sulfate and sulfite was its secondary pathway to produce hydrogen sulfide.[Conclusion] By revealing the mechanism of sulfide production from cysteine degradation by Citrobacter, this paper provides a theoretical basis for the prevention and control of sulfide in mariculture.
