MtrAB-LpqB: a conserved pathway regulating cell division in the phylum Actinobacteria?

Streptomyces are ubiquitous in soil and face a rapidly changing environment. Like other bacteria, they sense and respond to external stimuli via two component systems and Streptomyces species encode a particularly high number of these systems. One of these two component systems is called MtrAB-LpqB and it is highly conserved in the phylum Actinobacteria. Previous work in Mycobacterium tuberculosis, Corynebacterium glutamicum and Streptomyces coelicolor indicates that MtrAB-LpqB is involved in osmosensing and cell cycle progression. To investigate the function of MtrAB-LpqB I attempted to make single gene deletions in the new model organism Streptomyces venezuelae. I also performed chromatin immunoprecipitation and sequencing (ChIP-seq) against MtrA-3xFlag in S. venezuelae and S. coelicolor to identify the regulon of genes under its control. I present evidence that MtrA is essential in S. venezuelae whereas MtrB is dispensable. It was not possible to confirm deletion of lpqB. Deletion of mtrB activates MtrA and leads to the overproduction of cryptic secondary metabolite biosynthetic gene clusters (BGCs). The same effect was achieved by introducing a gain of function MtrA protein into the S. venezuelae wild-type strain. The cryptic BGCs are activated because MtrA binds to target genes spanning 85% of the BGCs in S. venezuelae and S. coelicolor. In Streptomyces, antibiotic production is linked to development and the MtrA regulon overlaps with the master regulator of development, BldD. The results presented here suggest that MtrAB senses external signals and modulates target gene expression to coordinate development with the production of secondary metabolites

The MtrAB two-component system controls antibiotic production in Streptomyces coelicolor A3(2

MtrAB is a highly conserved two-component system implicated in the regulation of cell division in the Actinobacteria. It coordinates DNA replication with cell division in the unicellular Mycobacterium tuberculosis and links antibiotic production to sporulation in the filamentous Streptomyces venezuelae. Chloramphenicol biosynthesis is directly regulated by MtrA in S. venezuelae and deletion of mtrB constitutively activates MtrA and results in constitutive over-production of chloramphenicol. Here we report that in Streptomyces coelicolor, MtrA binds to sites upstream of developmental genes and the genes encoding ActII-1, ActII-4 and RedZ, which are cluster-situated regulators of the antibiotics actinorhodin (Act) and undecylprodigiosin (Red). Consistent with this, deletion of mtrB switches on the production of Act, Red and streptorubin B, a product of the Red pathway. Thus, we propose that MtrA is a key regulator that links antibiotic production to development and can be used to upregulate antibiotic production in distantly related streptomycetes

The conserved actinobacterial two-component system MtrAB coordinates chloramphenicol production with sporulation in Streptomyces venezuelae NRRL B-65442

Streptomyces bacteria make numerous secondary metabolites, including half of all known antibiotics. Production of antibiotics is usually coordinated with the onset of sporulation but the cross regulation of these processes is not fully understood. This is important because most Streptomyces antibiotics are produced at low levels or not at all under laboratory conditions and this makes large scale production of these compounds very challenging. Here we characterise the highly conserved actinobacterial two-component system MtrAB in the model organism Streptomyces venezuelae and provide evidence that it coordinates production of the antibiotic chloramphenicol with sporulation. MtrAB are known to coordinate DNA replication and cell division in Mycobacterium tuberculosis where TB-MtrA is essential for viability. We were unable to delete mtrA in S. venezuelae unless another copy was present in trans but deletion of mtrB resulted in a global shift in the metabolome, including constitutive, high-level production of chloramphenicol. We found that chloramphenicol is detectable in the wild type strain, but only at very low levels and only after it has sporulated. ChIP-seq showed that MtrA binds upstream of DNA replication and cell division genes and genes required for chloramphenicol production. dnaA, dnaN, oriC and wblE (whiB1) appear to be targets for MtrA in both M. tuberculosis and S. venezuelae. Intriguingly, over-expression of TB-MtrA and gain of function TB- and Sv-MtrA proteins in S. venezuelae also switched on high level production of chloramphenicol. Given the conservation of MtrAB, these constructs might be useful tools for manipulating antibiotic production in other filamentous actinomycetes

Sensing and responding to diverse extracellular signals: An updated analysis of the sensor kinases and response regulators of Streptomyces spp

Streptomyces venezuelae is a Gram-positive, filamentous actinomycete with a complex developmental life cycle. Genomic analysis revealed that S. venezuelae encodes a large number of two-component systems (TCS): comprised of a membrane-bound sensor kinase (SK) and a cognate response regulator (RR). These proteins act together to detect and respond to diverse extracellular signals. Some of these systems have been shown to regulate antimicrobial biosynthesis in Streptomyces species, making them very attractive to researchers. The ability of S. venezuelae to sporulate in both liquid and solid cultures has made it an increasingly popular model organism in which to study these industrially and medically important bacteria. Bioinformatic analysis identified 58 TCS operons in S. venezuelae with an additional 27 orphan SK and 18 orphan RR genes. A broader approach identified 15 of the 58 encoded TCS to be highly-conserved in 93 Streptomyces species for which high quality and complete genome sequences are available. This review attempts to unify the current work on two-component systems in the streptomycetes, with an emphasis on S. venezuelae

Microbial composition and dynamics in environmental samples from a ready-to-eat food production facility with a long-term colonisation of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen of significant concern for the food industry due to its remarkable ability to persist through safety control efforts, posing a subsequent health threat to consumers. Understanding the microbial communities coexisting with L. monocytogenes in food processing environments provides insights into its persistence mechanisms. We investigated the microbial communities on non-food contact surfaces in a facility producing ready-to-eat foods, known to harbour a ST121 L. monocytogenes strain over multiple years. A 10-week sampling period was coordinated with the company and public health authorities. Metagenomic analysis revealed a stable microbial composition dominated by Pseudomonas fluorescens. While highly related populations were present in high-care production zones, distinctive taxa characteristic of specific areas were observed (e.g., Sphingomonas aerolata). Although Listeria spp. were not detected in metagenomes, they were detected in cultured samples, suggesting low relative abundance in factory settings. The findings suggest that a stable resident microbiota, with distinct adaptations to different areas within the factory, was selected for by their collective ability to survive control efforts in this environment. Listeria spp. was a member of this microbial community, albeit at low abundance, and may likewise benefit from the mutualism of the overall microbial community