Fnr Negatively Regulates Prodigiosin Synthesis in Serratia sp. ATCC 39006 During Aerobic Fermentation

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.

Global transcriptional regulator FNR regulates the pyruvate cycle and proton motive force to play a role in aminoglycosides resistance of Edwardsiella tarda

Bacterial metabolism is related to resistance and susceptibility to antibiotics. Fumarate and nitrate reduction regulatory protein (FNR) is a global transcriptional regulator that regulates metabolism. However, the role of FNR in antibiotic resistance is elusive. Here, fnr deletion mutant was constructed and used to test the role in Edwardsiella tarda EIB202 (EIB202). Δfnr exhibited elevated sensitivity to aminoglycosides. The mutant had a globally enhanced metabolome, with activated alanine, aspartate, and glutamate metabolism and increased abundance of glutamic acid as the most impacted pathway and crucial biomarker, respectively. Glutamate provides a source for the pyruvate cycle (the P cycle) and thereby relationship between exogenous glutamate-activated P cycle and gentamicin-mediated killing was investigated. The activated P cycle elevated proton motive force (PMF). Consistently, exogenous glutamate potentiated gentamicin-mediated killing to EIB202 as the similarity as the loss of FNR did. These findings reveal a previously unknown regulation by which FNR downregulates glutamate and in turn inactivates the P cycle, which inhibits PMF and thereby exhibits the resistance to aminoglycosides.

Biotechnological advances for improving natural pigment production: a state-of-the-art review

In current years, natural pigments are facing a fast-growing global market due to the increase of people's awareness of health and the discovery of novel pharmacological effects of various natural pigments, e.g., carotenoids, flavonoids, and curcuminoids. However, the traditional production approaches are source-dependent and generally subject to the low contents of target pigment compounds. In order to scale-up industrial production, many efforts have been devoted to increasing pigment production from natural producers, via development of both in vitro plant cell/tissue culture systems, as well as optimization of microbial cultivation approaches. Moreover, synthetic biology has opened the door for heterologous biosynthesis of pigments via design and re-construction of novel biological modules as well as biological systems in bio-platforms. In this review, the innovative methods and strategies for optimization and engineering of both native and heterologous producers of natural pigments are comprehensively summarized. Current progress in the production of several representative high-value natural pigments is also presented; and the remaining challenges and future perspectives are discussed.

Organic hydroperoxide induces prodigiosin biosynthesis in Serratia sp. ATCC 39006 in an OhrR-dependent manner

The biosynthesis of prodigiosin in the model prodigiosin-producing strain, Serratia sp. ATCC 39006, is significantly influenced by environmental and cellular signals. However, a comprehensive regulatory mechanism for this process has not been well established. In the present study, we demonstrate that organic hydroperoxide activates prodigiosin biosynthesis in an OhrR-dependent manner. Specifically, the MarR-family transcriptional repressor OhrR (Ser39006_RS05455) binds to its operator located far upstream of the promoter region of the prodigiosin biosynthesis operon (319-286 nt upstream of the transcription start site) and negatively regulates the expression of prodigiosin biosynthesis genes. Organic hydroperoxide disassociates the binding between OhrR and its operator, thereby promoting the prodigiosin production. Moreover, OhrR modulates the resistance of Serratia sp. ATCC 39006 to organic hydroperoxide by regulating the transcription of its own gene and the downstream co-transcribed ohr gene. These results demonstrate that OhrR is a pleiotropic repressor that modulates the prodigiosin production and the resistance of Serratia sp. ATCC 39006 to organic hydroperoxide stress. IMPORTANCE Bacteria naturally encounter various environmental and cellular stresses. Organic hydroperoxides generated from the oxidation of polyunsaturated fatty acids are widely distributed and usually cause lethal oxidative stress by damaging cellular components. OhrR is known as a regulator which modulates the resistance of bacteria to organic hydroperoxide stress. In the current study, organic hydroperoxide disassociates OhrR from the promoter of prodigiosin biosynthesis gene cluster, thus promoting transcription of pigA-O genes. In this model, organic hydroperoxide acts as an inducer of prodigiosin synthesis in Serratia sp. ATCC 39006. These results improve our understanding of the regulatory network of prodigiosin synthesis and serve as an example for identifying the cross-talk between the stress responses and the regulation of secondary metabolism.