The Mechanisms Of Synthesis Of Prodigiosin Involved In Cd²⁺ Tolerance And Elimination In Serratia Marcescens KMR-3

A strain of Serratia marcescens KMR-3 which was isolated by our previous research and have high efficiency of heavy metal tolerance and ability of production of prodigiosin was used in this study.The mechanisms of yynthesis of prodigiosin involved in Cd²⁺tolerance and elimination in Serratia Marcescens KMR-3 was investigated by several technologies in this study.At the first,the effect of Cd²⁺on KMR-3 production of was investigated by phenotype and high performance liquid chromatography.Meanwhile,transcriptome sequencing and RT-PCR technology have been used.Secondly,based on the resistance of KMR-3 toward heavy metal cadmium,the tolerance and removal mechanism of heavy metal cadmium in KMR-3 were studied.It was found that the synthesis of prodigiosin improved the resistant toward heavy metal cadmium.The research results are described as follows in detail:1.The Cd²⁺significantly inhibited production of prodigiosin in KMR-3.The synthesis of prodigiosin can be completely inhibited by Cd²⁺at concentration of 142(±10)mg/L.The synthesis of prodigiosin always occurred after 8 hours of cultivation of KMR-3.2.It has been illustrated that three major metabolic pathways were involve in the inhibitory of Cd²⁺on the synthesis of KMR-3 prodigiosin.First,Cd²⁺inhibited the production of prodigiosin promoters and precursor substances.The genes involved in aspartic acid and glutamic acid synthesis are down-regulated when Cd²⁺was added.The results of transcriptome analysis showed that genes involved in synthesis of arginine and proline were down-regulated,while some decomposed genes is up-regulated when Cd²⁺was added,resulting in less synthesis of arginine and proline.In addition,Cd²⁺also inhibited the expression of some genes involved in prodigiosin synthesis pathway and14 related genes have been suppressed.3.The synthetase gene of azi B2(pig F)and pps A(pig C)were significantly down-regulated up to 80%and 55%when Cd²⁺was added respectively,meanwhile the synthesis of phosphoenolpyruvate synthase/pyruvate phosphodikinase and SAM-dependent methyl transferase were decreased,which lead to synthesis of prodigiosin is reduced.The removal rate of Cd²⁺by KMR-3 is confirmed to be 93.57%.The removal is mainly dependent on intracellular absorption,supplemented with extracellular adsorption.Transcriptome analysis and RT-PCR analysis showed that several mechanisms related to resistance of KMR-3 to heavy metal cadmium have been involved:the expression of precursors related to flagella synthesis is enhanced,which can increase the mobility of KMR-3;gene expression related to biofilm formation is enhanced,which can effectively isolate or regulate the transport of harmful ions;the efflux of heavy metal cadmium based on P-type ATPase(related genes are znt R,znt A,znt B)and Znu protein chelation system(related genes include znu A,znu B,and znu C).Our result s indicated that two tolerance mechanisms effectively increased the resistance of KMR-3 toward heavy metal cadmium.