Regulation of Nir gene in Lactobacillus plantarum WU14 mediated by GlnR

Transcriptional Analysis and Identification of a Peptidoglycan Hydrolase (PGH) and a Ribosomal Protein with Antimicrobial Activity Produced by Lactiplantibacillus paraplantarum

The growing challenge of antibiotic resistance has intensified the search for new antimicrobial agents. Promising alternatives include peptidoglycan hydrolases (PGHs) and certain ribosomal proteins, both of which exhibit antimicrobial activity. This study focuses on a Lactiplantibacillus paraplantarum strain, isolated from fermented meat, capable of inhibiting pathogens such as Listeria innocua, Salmonella Typhimurium, Escherichia coli, Staphylococcus aureus, and Weissella viridescens. The highest growth and antimicrobial activity were observed at a high nitrogen concentration (5.7 g/L). Two antimicrobial proteins were identified: the 50S ribosomal protein L14 (RP uL14) and 6-phospho-N-acetylmuramidase (MupG), a PGH. Partial purification and characterization of these proteins were achieved using SDS-PAGE, zymography, and LC-MS/MS. Transcriptional data (RT-qPCR) showed that higher nitrogen concentrations enhanced MupG expression, while increased carbon concentrations boosted RP uL14 expression. These findings highlight the importance of nutritional sources in maximizing the production of novel antimicrobial proteins, offering a potential path to develop effective alternatives against antibiotic-resistant bacteria.

Regulation mechanism of nitrite degradation in Lactobacillus plantarum WU14 mediated by Fnr

Fumarate and nitrate reduction regulatory protein (Fnr)-a global transcriptional regulator-can directly or indirectly regulate many genes in different metabolic pathways at the top of the bacterial transcription regulation network. The present study explored the regulatory mechanism of Fnr-mediated nitrite degradation in Lactobacillus plantarum WU14 through gene transcription and expression analysis of oxygen sensing and nir operon expression regulation by Fnr. The interaction and the mechanism of transcriptional regulation between Fnr and GlnR were also examined under nitrite stress. After Fnr and GlnR purification by glutathione S-transferase tags, they were successfully expressed in Escherichia coli by constructing an expression vector. The results of electrophoresis mobility shift assay and qRT-PCR indicated that Fnr specifically bound to the PglnR and Pnir promoters and regulated the expression of nitrite reductase (Nir) and GlnR. After 6-12 h of culture, the expressions of fnr and nir under anaerobic conditions were higher than under aerobic conditions; the expression of these two genes increased with sodium nitrite (NaNO2) addition during aerobic culture. Overall, the present study indicated that Fnr not only directly participated in the expression of Nir and GlnR but also indirectly regulated the expression of Nir through GlnR regulation.

Regulation of PhoB on biofilm formation and hemolysin gene hlyA and ciaR of Streptococcus agalactiae

PhoB is a response regulator protein that plays a key role in the PhoBR two-component signal transduction system. In this study, we used transcriptome and proteomics techniques to evaluate the detect the gene network regulated by PhoB of Streptococcus agalactiae. The results showed that expression of biofilm formation and virulence-related genes were changed after phoB deficiency. Crystal violet and CLSM assay confirmed that the deletion of the phoB increased the thickness of S. agalactiae biofilm. The results of lacZ reporter and the bacterial one-hybridization method showed that PhoB could directly bind to the promoter regions of hemolysin A and ciaR genes but not to the promoter regions of cylE and hemolysin III. Through the construction of an 18-base pair deoxyribose nucleic acid (DNA) random fragment library and the bacterial one-hybridization system, it was found that the conservative sequence of PhoB binding was TTGGAGAA(G/T). Our research has uncovered the virulence potential of the PhoBR two-component system of S. agalactiae. The findings of this study provide the theoretical foundation for in-depth research on the pathogenic mechanism of S. agalactiae.

Lactiplantibacillus brownii sp. nov., a novel psychrotolerant species isolated from sauerkraut

A Gram-stain-positive, rod-shaped, facultatively anaerobic and homofermentative strain, named WILCCON 0030T, was isolated from sauerkraut (fermented cabbage) collected from a local market in the Moscow region of Russia. Comparative analyses based on 16S rRNA gene sequence similarity and whole genome relatedness indicated that strain WILCCON 0030T was most closely related to the type strains Lactiplantibacillus nangangensis NCIMB 15186T, Lactiplantibacillus daoliensis LMG 31171T and Lactiplantibacillus pingfangensis LMG 31176T. However, the average nucleotide identity and digital DNA-DNA hybridization prediction values with these closest relatives only ranged from 84.6 to 84.9 % and from 24.1 to 24.7 %, respectively, and were below the 95.0 and 70.0% thresholds for species delineation. Substantiated by further physiological and biochemical analyses, strain WILCCON 0030T represents a novel species within the genus Lactiplantibacillus for which we propose the name Lactiplantibacillus brownii sp. nov. (type strain WILCCON 0030T=DSM 116485T=LMG 33211T).

Research progress on GlnR-mediated regulation in Actinomycetes

This review constitutes a summary of current knowledge on GlnR, a global regulator, that assumes a critical function in the regulation of nitrogen metabolism of Actinomycetes. In cross-regulation with other regulators, GlnR was also shown to play a role in the regulation of carbon and phosphate metabolisms as well as of secondary metabolism. A description of the structure of the GlnR protein and of its binding sites in various genes promoters regions is also provided. This review thus provides a global understanding of the critical function played by GlnR in the regulation of primary and secondary metabolism in Actinomycetes.