Positive Autoregulation Of Dkp-luxr Type Quorum Sensing System In Spoilage Potential And Biofilm Formation Of Shewanella Baltica

Large yellow croaker(Pseudosciaene crocea)is a popular seafood with high nutrition and great commercial value.Shewanalla baltica 73 was isolated from large yellow croaker stored at 4 ? and was demonstrated as the specific spoilage organism(SSO),whose spoilage potential was supposed to be regulated by Quorum sensing(QS)system.However,the QS autoinducers and receptors in S.baltica are not fully understood,and the specific regulation network between QS system and spoilage has not been revealed.In the present study,we first identified six luxxR-type genes in S.baltica 73 whole genome through BLAST,and verified their role in QS by autoregulation experiments.The hypothetical QS signals produced by S.baltica 73 were identified by UPLC-MS/MS,among which cyclo-(L-Pro-L-Phe)(PP)was the predominant one according to LuxR01 and LuxR02 binding assay.Deletion of luxR-type genes or c-di-GMP-related gene bfp impaired spoilage potential and biofilm formation of S.baltica 73.Consistently,exogenous PP promoted these effects,which could also be attenuated by luxR01 or luxR02 deletion.Transcriptional analysis showed that spoilage and biofilm-related genes torS,speF and pomA were down-regulated in luxR01 and luxR02 deletion strains,and that torS and speF were also down-regulated in QS-independent bfp deletion strain.Our results revealed torS,pomA and speF as the downstream genes of LuxR-type QS system and the second messenger-mediated biofilm formation were responsible for spoilage activity in S.baltica 73,giving an insight into the mechanism underlying the correlation between QS,biofilm and spoilage,and sheding light on the improvement of seafood preservation.The physiological and clinical aspects of QS have attracted considerable attention and been investigated at the molecular level,and there are many QS systems that involve a transcriptional activator,which responds to an acyl-homoserine lactone signal.Here,we used the SSO of large yellow croaker S.baltica as a model to explore the role of QS system in food quality,and found the positive autoregulation of DKP-LuxR-dependent QS system in spoilage potential and biofilm formation,which expanded the knowledge of QS system and gave a new insight into the improvement of food preservation.