Two component system CpxR/A regulates the prodigiosin biosynthesis by negative control in Serratia marcescens FS14

Reduced OxyR positively regulates the prodigiosin biosynthesis in Serratia marcescens FS14

OxyR, a LysR family transcriptional regulator, plays vital roles in bacterial oxidative stress response. In this study, we found that the deletion of oxyR not only inhibited the antioxidant capacity of S. marcescens FS14, but also decreased the production of prodigiosin. Further study revealed that OxyR activated the prodigiosin biosynthesis at the transcriptional level. Complementary results showed that not only the wild-type OxyR but also the reduced form OxyRC199S could activate the prodigiosin biosynthesis. We further demonstrated that reduced form of wild type OxyR could bind to the promoter of pig gene cluster, and identified the binding sites which is different from oxidized OxyR binding sites in E. coli. Our results demonstrated that OxyR in FS14 uses oxidized form to regulate the expression of the antioxidant related genes and utilizes reduced form to activate prodigiosin production. Further in silico analysis suggested that the activation of prodigiosin biosynthesis by reduced OxyR should be general in S. marcesencs. To our knowledge, this is the first report to show that OxyR uses the reduced form to activate the gene's expression, therefore, our results provide a novel regulation mechanism of OxyR.

Multicopy expression of sigma factor RpoH reduces prodigiosin biosynthesis in Serratia marcescens FS14

Regulation of prodigiosin biosynthesis is received wide attention due to the antimicrobial, immunosuppressive and anticancer activities of prodigiosin. Here, we constructed a transposon mutant library in S. marcescens FS14 to identify genes involved in the regulation of prodigiosin biosynthesis. 62 strains with apparently different colors were obtained. Identification of the transposon insertion sites revealed that they are classified into three groups: the coding region of cyaA and two component system eepS/R and the promoter region of rpoH. Since the effect of cyaA and eepS/R genes on prodigiosin was extensively investigated in Serratia marcescens, we chose the mutant of rpoH for further investigation. Further deletion mutation of rpoH gene showed no effect on prodigiosin production suggesting that the effect on prodigiosin production caused by transposon insertion is not due to the deletion of RpoH. We further demonstrated that multicopy expression of RpoH reduced prodigiosin biosynthesis indicating that transposon insertion caused RpoH enhanced expression. Previous results indicate that RpoS is the sigma factor for transcription of pig gene cluster in FS14, to test whether the enhanced expression of RpoH prevents prodigiosin by competing with RpoS, we found that multicopy expression of RpoS could alleviate the prodigiosin production inhibition by enhanced RpoH. We proposed that multicopy expressed RpoH competes with RpoS for core RNA polymerase (RNAP) resulting in decreased transcription of pig gene cluster and prodigiosin production reduction. We also demonstrated that RpoH is not directly involved in prodigiosin biosynthesis. Our results suggest that manipulating the transcription level of sigma factors may be applied to regulate the production of secondary metabolites.

Transcriptional factor OmpR positively regulates prodigiosin biosynthesis in Serratia marcescens FZSF02 by binding with the promoter of the prodigiosin cluster

Prodigiosin is a promising secondary metabolite mainly produced by Serratia marcescens. The production of prodigiosin by S. marcescens is regulated by different kinds of regulatory systems, including the EnvZ/OmpR system. In this study, we demonstrated that the regulatory factor OmpR positively regulated prodigiosin production in S. marcescens FZSF02 by directly binding to the promoter region of the prodigiosin biosynthesis cluster with a lacZ reporter assay and electrophoretic mobility shift assay (EMSA). The binding sequence with the pig promoter was identified by a DNase I footprinting assay. We further demonstrate that OmpR regulates its own expression by directly binding to the promoter region of envZ/ompR. For the first time, the regulatory mechanism of prodigiosin production by the transcriptional factor OmpR was revealed.