Biology subjects

Muh, U.

Publications and source records attributed to Muh, U..

5 recordsLinked to original sources

bioRxiv2024

Identification of a new family of peptidoglycan transpeptidases reveals atypical crosslinking is essential for viability in Clostridioides difficile

Clostridioides difficile, the leading cause of antibiotic-associated diarrhea, relies primarily on 3-3 crosslinks created by L,D-transpeptidases (LDTs) to fortify its peptidoglycan (PG) cell wall. This is unusual, as in most bacteria the vast majority of PG crosslinks are 4-3 crosslinks, which are created by penicillin-binding proteins (PBPs). Here we report the unprecedented observation that 3-3 crosslinking is essential for viability in C. difficile. We also report the discovery of a new family of LDTs that use a VanW domain to catalyze 3-3 crosslinking rather than a YkuD domain as in all previously known LDTs. Bioinformatic analyses indicate VanW domain LDTs are less common than YkuD domain LDTs and are largely restricted to Gram-positive bacteria. Our findings suggest that LDTs might be exploited as targets for antibiotics that kill C. difficile without disrupting the intestinal microbiota that is important for keeping C. difficile in check.

microbiology↗

bioRxiv2022

The WalRK Two-component system is Essential for Proper Cell Envelope Biogenesis in Clostridioides difficile

The WalR-WalK two-component regulatory system (TCS) is found in all Firmicutes, where it regulates the expression of multiple genes required for remodeling the cell envelope during growth and division. Unlike most TCSs, WalRK is essential for viability, so it has attracted interest as a potential antibiotic target. Here we used overexpression of WalR and CRISPR interference to investigate the Wal system of Clostridioides difficile, a major cause of hospital-associated diarrhea in high-income countries. We confirmed the wal operon is essential and identified morphological defects and cell lysis as the major terminal phenotypes of altered wal expression. We also used RNA-seq to identify over 150 genes whose expression changes in response to WalR levels. This gene set is enriched in cell envelope genes and includes several predicted PG hydrolases and proteins that could regulate PG hydrolase activity. A distinct feature of the C. difficile cell envelope is the presence of an S-layer and we found WalR affects expression of several genes which encode S-layer proteins. An unexpected finding was that some Wal-associated phenotypic defects were inverted in comparison to what has been reported in other Firmicutes. For example, down-regulation of Wal signaling caused C. difficile cells to become longer rather than shorter, as in Bacillus subtilis. Likewise, down-regulation of Wal rendered C. difficile more sensitive to vancomycin, whereas reduced Wal activity is linked to increased vancomycin resistance in Staphylococcus aureus. ImportanceThe WalRK two-component system (TCS) is essential for coordinating synthesis and turnover of peptidoglycan in Firmicutes. Here we investigate the WalRK TCS in Clostridioides difficile, an important bacterial pathogen with an atypical cell envelope. We confirmed that WalRK is essential and regulates cell envelope biogenesis, although several of the phenotypic changes we observed were opposite to what has been reported in other Firmicutes. We also identified over 150 genes whose expression is controlled either directly or indirectly by WalR. Overall, our findings provide a foundation for future investigations of an important regulatory system and potential antibiotic target in C. difficile.

microbiology↗

bioRxiv2020

Lysozyme resistance in C. difficile is dependent on two peptidoglycan deacetylases

Clostridioides (Clostridium) difficile is a major cause of hospital-acquired infections leading to antibiotic-associated diarrhea. C. difficile exhibits a very high level of resistance to lysozyme. Bacteria commonly resist lysozyme through modification of the cell wall. In C. difficile {sigma}V is required for lysozyme resistance and {sigma}V is activated in response to lysozyme. Once activated {sigma}V, encoded by csfV, directs transcription of genes necessary for lysozyme resistance. Here we analyze the contribution of individual genes in the csfV regulon to lysozyme resistance. Using CRISPR-Cas9 mediated mutagenesis we constructed in-frame deletions of single genes in the csfV operon. We find pdaV, which encodes a peptidoglycan deacetylase, is partially responsible for lysozyme resistance. We then performed CRISPR inhibition (CRISPRi) to identify a second peptidoglycan deacetylase, pgdA, that is important for lysozyme resistance. Deletion of either pgdA or pdaV resulted in modest decreases in lysozyme resistance. However, deletion of both pgdA and pdaV resulted in a 1000-fold decrease in lysozyme resistance. Further, muropeptide analysis revealed loss of either PgdA or PdaV had modest effects on peptidoglycan deacetylation but loss of both PgdA and PdaV resulted in almost complete loss of peptidoglycan deacetylation. This suggests that PgdA and PdaV are redundant peptidoglycan deacetylases. We also use CRISPRi to compare other lysozyme resistance mechanisms and conclude that peptidoglycan deacetylation is the major mechanism of lysozyme resistance in C. difficile. ImportanceClostridioides difficile is the leading cause of hospital-acquired diarrhea. C. difficile is highly resistant to lysozyme. We previously showed that the csfV operon is required for lysozyme resistance. Here we use CRISPR-Cas9 mediated mutagenesis and CRISPRi knockdown to show that peptidoglycan deacetylation is necessary for lysozyme resistance and is the major lysozyme resistance mechanism in C. difficile. We show that two peptidoglycan deacetylases in C. difficile are partially redundant and are required for lysozyme resistance. PgdA provides an intrinsic level of deacetylation and PdaV, encoded as part of the csfV operon, provides lysozyme-induced peptidoglycan deacetylation.

microbiology↗

bioRxiv2019

Activation of the Extracytoplasmic Function σ factor σP by β-lactams in Bacillus thuringiensis requires the site-2 protease RasP

Bacteria can utilize alternative {sigma} factors to regulate sets of genes in response to changes in the environment. The largest and most diverse group of alternative {sigma} factors are the Extracytoplasmic Function (ECF) {sigma} factors. {sigma}P is an ECF {sigma} factor found in Bacillus anthracis, B. cereus, and B. thuringiensis. Previous work showed {sigma}P is induced by ampicillin, a {beta}-lactam antibiotic, and required for resistance to ampicillin. However, it was not known how activation of {sigma}P is controlled or what other antibiotics may activate {sigma}P. Here we report that activation of {sigma}P is specific to a subset of {beta}-lactams and {sigma}P is required for resistance to these {beta}-lactams. We demonstrate that activation of {sigma}P is controlled by the proteolytic destruction of the anti-{sigma} factor, RsiP, and that degradation of RsiP requires multiple proteases. Upon exposure to {beta}-lactams, the extracellular domain of RsiP is cleaved by an unknown protease, which we predict cleaves at site-1. Following cleavage by the unknown protease, the N-terminus of RsiP is further degraded by the site-2 intramembrane protease, RasP. Our data indicate that RasP cleavage of RsiP is not the rate-limiting step in {sigma}P activation. This proteolytic cascade leads to activation of {sigma}P which induces resistance to {beta}-lactams likely via increased expression of {beta}-lactamases.\n\nImportanceThe discovery of antibiotics to treat bacterial infections has had a dramatic and positive impact on human health. However, shortly after the introduction of a new antibiotic bacteria often develop resistance. The bacterial cell envelope is essential for cell viability and is the target of many of the most commonly used antibiotics including {beta}-lactam antibiotics. Resistance to {beta}-lactams is often dependent upon {beta}-lactamases. In B. cereus, B. thuringiensis and some B. anthracis strains the expression of some {beta}-lactamases is inducible. This inducible {beta}-lactamase expression is controlled by activation of an alternative {sigma} factor called {sigma}P. Here we show that {beta}-lactam antibiotics induce {sigma}P activation by degradation of the anti-{sigma} factor RsiP.

microbiology↗

bioRxiv2018

A xylose-inducible expression system and a CRISPRi-plasmid for targeted knock-down of gene expression in Clostridioides difficile

Here we introduce plasmids for xylose-regulated expression and repression of genes in Clostridioides difficile. The xylose-inducible expression vector allows for ~100-fold induction of an mCherryOpt reporter gene. Induction is titratable and uniform from cell-to-cell. The gene repression plasmid is a CRISPR-interference (CRISPRi) system based on a nuclease-defective, codon-optimized allele of the Streptococcus pyogenes Cas9 protein (dCas9) that is targeted to a gene of interest by a constitutively-expressed single guide RNA (sgRNA). Expression of dCas9 is induced by xylose, allowing investigators to control the timing and extent of gene-silencing, as demonstrated here by dose-dependent repression of a chromosomal gene for a red fluorescent protein (maximum repression ~100-fold). To validate the utility of CRISPRi for deciphering gene function in C. difficile, we knocked-down expression of three genes involved in biogenesis of the cell envelope: the cell division gene ftsZ, the S-layer protein gene slpA and the peptidoglycan synthase gene pbp-0712. CRISPRi confirmed known or expected phenotypes associated with loss of FtsZ and SlpA, and revealed that the previously uncharacterized peptidoglycan synthase PBP-0712 is needed for proper elongation, cell division and protection against lysis.\n\nImportanceClostridioides difficile has become the leading cause of hospital-acquired diarrhea in developed countries. A better understanding of the basic biology of this devastating pathogen might lead to novel approaches for preventing or treating C. difficile infections. Here we introduce new plasmid vectors that allow for titratable induction (Pxyl) or knockdown (CRISPRi) of gene expression. The CRISPRi plasmid allows for easy depletion of target proteins in C. difficile. Besides bypassing the lengthy process of mutant construction, CRISPRi can be used to study the function of essential genes, which are particularly important targets for antibiotic development.

microbiology↗