Abstract
Serratia marcescens, a gram-negative bacterium, found in a wide range of ecological niches can produce several high-value products, including prodigiosin, althiomycin, and serratamolide. Among them, prodigiosin has attracted attention due to its immunosuppressive, antimicrobial, and anticancer properties. However, the regulatory mechanisms behind prodigiosin synthesis in Serratia marcescens remains limited. Here, a transposon mutant library was constructed to identify the genes related to prodigiosin synthesis, and BVG90_02415 gene encoding a peptidoglycan synthesizing enzyme D-Ala-D-Ala carboxypeptidase DacA was found to negatively regulates prodigiosin synthesis. Quantitative measurements revealed that disruption of dacA increased prodigiosin production 1.46-fold that of the wild-type strain JNB5-1 in fermentation medium. By comparing differences in cell growth, pigA gene expression level, cell morphology, membrane permeability, and intracellular prodigiosin concentration between wild-type strain JNB5-1 and dacA mutant SK4-72, results revealed that the mechanism for hyper-producing of prodigiosin by the dacA mutant was probably that dacA disruption enhanced prodigiosin leakage, which in turn alleviated feedback inhibition of prodigiosin and increased expression of pig gene cluster. Collectively, this work provides a novel insight into regulatory mechanisms of prodigiosin synthesis and uncovers new roles of DacA protein in regulating cell growth, cell morphology, and membrane permeability in Serratia marcescens. Finally, this study offers a new strategy for improving production of high-value compounds in Serratia marcescens.
Highlights
Serratia marcescens (S. marcescens), is a gram-negative rod-shaped bacterium of the Enterobacteriaceae family found in a wide range of environments like soil, water, plants, insects, foods, and machinery (Abreo and Altier, 2019)
The prodigiosin biosynthesis pathway consists of a total of 14 genes, named pigA, pigB, pigC, pigD, pigE, pigF, pigG, pigH, pigI, pigJ, pigK, pigL, pigM, and pigN, whereby the pigB, pigD, and pigE genes are responsible for the synthesis of monopyrrole moiety (MAP), while the pigA, pigF, pigG, pigH, pigI, pigJ, pigM, and pigN genes are responsible for the synthesis of bipyrrole moiety (MBC)
To identify the genes involved in prodigiosin synthesis in S. marcescens, a random Tn5G transposon insertion library using E. coli/pRK2013 Tn5G as the donor strain and S. marcescens JNB5-1 as the recipient strain was constructed, and nearly 20,000 mutants were collected (Figure 1A)
Summary
Serratia marcescens (S. marcescens), is a gram-negative rod-shaped bacterium of the Enterobacteriaceae family found in a wide range of environments like soil, water, plants, insects, foods, and machinery (Abreo and Altier, 2019). In S. marcescens, the synthesis of prodigiosin is controlled by several transcriptional regulators, including positive regulators EepR (Shanks et al, 2017), PigP (Shanks et al, 2013), SmaI (Coulthurst et al, 2006), GumB (Stella et al, 2018), and RbsR (Lee et al, 2017), and negative regulators CopA (Williamson et al, 2006b), CRP (Stella and Shanks, 2014), HexS (Stella et al, 2012), RssB (Horng et al, 2010), and SpnR (Horng et al, 2002). CRP directly binds to the promoter region of the eepR gene, and negatively regulates the synthesis of prodigiosin
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