Isolating promoters from Corynebacterium ammoniagenes ATCC 6871 and application in CoA synthesis

Developing a High-Umami, Low-Salt Soy Sauce through Accelerated Moromi Fermentation with Corynebacterium and Lactiplantibacillus Strains

The traditional fermentation process of soy sauce employs a hyperhaline model and has a long fermentation period. A hyperhaline model can improve fermentation speed, but easily leads to the contamination of miscellaneous bacteria and fermentation failure. In this study, after the conventional koji and moromi fermentation, the fermentation broth was pasteurized and diluted, and then inoculated with three selected microorganisms including Corynebacterium glutamicum, Corynebacterium ammoniagenes, and Lactiplantibacillus plantarum for secondary fermentation. During this ten-day fermentation, the pH, free amino acids, organic acids, nucleotide acids, fatty acids, and volatile compounds were analyzed. The fermentation group inoculated with C. glutamicum accumulated the high content of amino acid nitrogen of 0.92 g/100 mL and glutamic acid of 509.4 mg/100 mL. The C. ammoniagenes group and L. plantarum group were rich in nucleotide and organic acid, respectively. The fermentation group inoculated with three microorganisms exhibited the best sensory attributes, showing the potential to develop a suitable fermentation method. The brewing speed of the proposed process in this study was faster than that of the traditional method, and the umami substances could be significantly accumulated in this low-salt fermented model (7% w/v NaCl). This study provides a reference for the low-salt and rapid fermentation of seasoning.

A Novel Method to Screen Strong Constitutive Promoters in Escherichia coli and Serratia marcescens for Industrial Applications

Promoters serve as the switch of gene transcription, playing an important role in regulating gene expression and metabolites production. However, the approach to screening strong constitutive promoters in microorganisms is still limited. In this study, a novel method was designed to identify strong constitutive promoters in E. coli and S. marcescens based on random genomic interruption and fluorescence-activated cell sorting (FACS) technology. First, genomes of E. coli, Bacillus subtilis, and Corynebacterium glutamicum were randomly interrupted and inserted into the upstream of reporter gene gfp to construct three promoter libraries, and a potential strong constitutive promoter (P_BS) suitable for E. coli was screened via FACS technology. Second, the core promoter sequence (P_BS76) of the screened promoter was identified by sequence truncation. Third, a promoter library of P_BS76 was constructed by installing degenerate bases via chemical synthesis for further improving its strength, and the intensity of the produced promoter P_BS76-100 was 59.56 times higher than that of the promoter P_{BBa_J23118}. Subsequently, promoters P_BBa__J23118, P_BS76, P_BS76-50, P_BS76-75, P_BS76-85, and P_BS76-100 with different strengths were applied to enhance the metabolic flux of L-valine synthesis, and the L-valine yield was significantly improved. Finally, a strong constitutive promoter suitable for S. marcescens was screened by a similar method and applied to enhance prodigiosin production by 34.81%. Taken together, the construction of a promoter library based on random genomic interruption was effective to screen the strong constitutive promoters for fine-tuning gene expression and reprogramming metabolic flux in various microorganisms.

Improving prodigiosin production by transcription factor engineering and promoter engineering in Serratia marcescens

Prodigiosin (PG), a red linear tripyrrole pigment produced by Serratia marcescens, has attracted attention due to its immunosuppressive, antimicrobial, and anticancer properties. Although many studies have been used to dissect the biosynthetic pathways and regulatory network of prodigiosin production in S. marcescens, few studies have been focused on improving prodigiosin production through metabolic engineering in this strain. In this study, transcription factor engineering and promoter engineering was used to promote the production of prodigiosin in S. marcescens JNB5-1. Firstly, through construing of a Tn5G transposon insertion library of strain JNB5-1, it was found that the DNA-binding response regulator BVG89_19895 (OmpR) can promote prodigiosin synthesis in this strain. Then, using RNA-Seq analysis, reporter green fluorescent protein analysis and RT-qPCR analysis, the promoter P17 (P_RplJ) was found to be a strong constitutive promoter in strain JNB5-1. Finally, the promoter P17 was used for overexpressing of prodigiosin synthesis activator OmpR and PsrA in strain JNB5-1 and a recombinant strain PG-6 was obtained. Shake flask analysis showed that the prodigiosin titer of this strain was increased to 10.25 g/L, which was 1.62-times that of the original strain JNB5-1 (6.33 g/L). Taken together, this is the first well-characterized constitutive promoter library from S. marcescens, and the transcription factor engineering and promoter engineering can be also useful strategies to improve the production of other high value-added products in S. marcescens.