Biodegradation Of Sulfonamides By Shewanella Oneidensis MR-1 And Shewanella Sp.strain MR-4

Sulfonamides?SAs?as chemical drugs for prevention and treatment of bacterial infectious diseases have been widely used in veterinary and clinical,a increasing attention was paid to the pollution problem.The microbial degradation method because of its mild and no pollution,simple operation and other characteristics has gradually become a research hotspot.The degradation of sulfonamides by microbial was affected by many environmental factors,such as initial concentration,pH,antibiotics,microorganisms and other influence factors.Dissimilatory iron-reducing bacteria can use Fe?III?as a terminal electron acceptor to respiratory.Dissimilatory iron-reducing bacteria could degrade a variety of pollutants.In this study,the resistance in Shewanella oneidensis MR-1 and Shewanella sp.strain MR-4 to the sulfonamides sulfapyridine?SPY?and sulfamethoxazole?SMX?were determined,and sulfonamides degradation by these strains was assessed.Different environmental factors were studied under laboratory condition.The results can be a guidance for the bioremediation of sulfonamide-polluted environments.The main research contents and results are as follows:1.To evaluate the antibiotic resistance of different concentrations of SPY and SMX in S.oneidensis MR-1 and Shewanella sp.strain MR-4,the increasing concentrations SPY and SMX on the inhibition of bacterial growth was studied.The growth of S.oneidensis MR-1 and Shewanella sp.strain MR-4 was inhibited by the addition of SPY or SMX to the medium.The growth of S.oneidensis MR-1 and Shewanella sp.strain MR-4 significantly reduced as the sulfonamide concentration increased.When the sulfonamide concentration was 60 mg/L,there was almost no colony growth.2.About 23.91% and 23.43% of SPY and 59.88% and 63.89% of SMX was degraded by S.oneidensis MR-1 and Shewanella sp.strain MR-4 in pure culture conditions,respectively,after incubation for 5 days.Further,2-aminopyridine?2-AP?was enriched in the media with SPY degradation,and SMX degradation led to the accumulation of 3-amino-5-methyl-isoxazole?3A5MI?.Effects of different environmental factors on the degradation of the sulfonamides were investigated.The results showed that the higher initial concentration,the degradation rate of two kinds of bacteria were decreased.At initial sulfonamide concentrations of 50 mg/L,we observed almost no degradation by either strain.Thus,the biodegradation of the two sulfonamides was significantly inhibited by a high initial concentration.The degradation rate was significantly affected by the initial pH,and it declinedsignificantly at around pH 7.0-8.0.After incubation in media containing five for 5days,SMX and SPY were preferentially utilized by strains as carbon and nitrogen sources and the order of the removal rates by two Shewanella was SMX > SPY>ST >SM2 >SDZ.When the degradation of SPY and SMX by the two strains mixed have synergistic effect.3.Adding Fe?III?can promote the degradation of the sulfonamides by S.oneidensis MR-1 and Shewanella sp.strain MR-4.About 53.5% and 66.02% of SPY were degraded by S.oneidensis MR-1 and Shewanella sp.strain MR-4 after adding Fe?III?,respectively.The degradation of SMX was almost 100% by two strains after 3 days.The concentration of Fe?II?was 1.91 mmol/L and 2.33 mmol/L by S.oneidensis MR-1 and Shewanella sp.strain MR-4 respectively.There were different degrees of inhibitory effects on the reduction and degradation of sulfonamides by two strains when adding other heavy metals(Pb²⁺,Cd²⁺,Zn²⁺,Hg²⁺)?To expore the effect of adding As?V?on the degradation of sulfonamides by S.oneidensis MR-1,after 5days,As?V?reduction rate was 0%,and the degradation of SPY and SMX was15.10% and 38.71%,respectively.S.oneidensis MR-1 does not have the dissimilatory reduction of As?V?.When adding As?V?to the system of Shewanella sp.strain MR-4and sulfonamides,As?V?reduction rate was14.21%,and the degradation of SPY and SMX was 19.80% and 40.71%.The results suggested that Shewanella sp.strain MR-4have ability to reduce As?V?.The co-existence of As?V?and sulfonamides maybe have a synergistic effect on the degradation of two sulfonamides4.The degradation products of SPY and SMX by S.oneidensis MR-1 and Shewanella sp.strain MR-4 were analyzed by LC-MS,with SPY as a substrate,2-AP?2-aminopyridine?was the main stable metabolite,and with SMX as a substrate,3A5MI?3-amino-5-methyl-isoxazole?was the main stable metabolite.The co-occurrence of 2-AP or 3A5 MI and 4-aminobenzenesulfonic acid suggests that the initial step in the biodegradation of the two sulfonamides is S–N bond cleavage.