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Cyclopropane Modification of Trehalose Dimycolate Drives Granuloma Angiogenesis and Mycobacterial Growth through Vegf Signaling.

Cell Host Microbe. 2018 10 10;24(4):514-525.e6

Authors: Walton EM, Cronan MR, Cambier CJ, Rossi A, Marass M, Foglia MD, Brewer WJ, Poss KD, Stainier DYR, Bertozzi CR, Tobin DM

Abstract
Mycobacterial infection leads to the formation of characteristic immune aggregates called granulomas, a process accompanied by dramatic remodeling of the host vasculature. As granuloma angiogenesis favors the infecting mycobacteria, it may be actively promoted by bacterial determinants during infection. Using Mycobacterium marinum-infected zebrafish as a model, we identify the enzyme proximal cyclopropane synthase of alpha-mycolates (PcaA) as an important bacterial determinant of granuloma-associated angiogenesis. cis-Cyclopropanation of mycobacterial mycolic acids by pcaA drives the activation of host Vegf signaling within granuloma macrophages. Cyclopropanation of the mycobacterial cell wall glycolipid trehalose dimycolate is both required and sufficient to induce robust host angiogenesis. Inducible genetic inhibition of angiogenesis and Vegf signaling during granuloma formation results in bacterial growth deficits. Together, these data reveal a mechanism by which PcaA-mediated cis-cyclopropanation of mycolic acids promotes bacterial growth and dissemination in vivo by eliciting granuloma vascularization and suggest potential approaches for host-directed therapies.

PMID: 30308157 [PubMed - indexed for MEDLINE]

Pathogen elimination by probiotic Bacillus via signalling interference

Pathogen elimination by probiotic <i>Bacillus</i> via signalling interference, Published online: 10 October 2018; doi:10.1038/s41586-018-0616-y

Lipopeptides secreted by Bacillus bacteria block quorum sensing by Staphylococcus aureus and thereby inhibit the growth of this opportunistic pathogen in the gut, suggesting why people in rural Thailand who are colonized by Bacillus are not also colonized by S. aureus.

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Chemistry-driven glycoscience.

Bioorg Med Chem. 2018 10 15;26(19):5229-5238

Authors: Kiessling LL

Abstract
Carbohydrates are the most prominent features of the cell's exterior-they are the cell's "face" and serve as the cell's identification card. The features of cell surface glycans (e.g. glycoproteins, glycolipids, polysaccharides) can be read by proteins, other cells, or organisms. In all of these contexts, glycan-binding proteins typically recognize ("read") glycan identity. This recognition mediates important host-microbe interactions, as well as critical physiological functions, including fertilization, development, and immune system function. This article focuses on how proteins recognize glycans with an emphasis on three objectives: 1) to understand the molecular basis for carbohydrate recognition, 2) to implement that understanding to develop functional probes of protein-carbohydrate interactions, and 3) to apply those probes to elucidate and exploit the physiological consequences of protein-carbohydrate interactions. In this context, our group has focused on two key aspects of carbohydrate recognition: CH-π and multivalent interactions. We are applying the foundational knowledge gained from our studies for purposes ranging from illuminating host-microbe interactions to probing immune system function.

PMID: 30297120 [PubMed - indexed for MEDLINE]

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Spatial control of cell envelope biosynthesis in mycobacteria.

Pathog Dis. 2018 06 01;76(4):

Authors: Puffal J, García-Heredia A, Rahlwes KC, Siegrist MS, Morita YS

Abstract
The mycobacterial cell envelope is a complex multilayered structure that provides the strength to the rod-shaped cell and creates the permeability barrier against antibiotics and host immune attack. In this review, we will discuss the spatial coordination of cell envelope biosynthesis and how plasma membrane compartmentalization plays a role in this process. The spatial organization of cell envelope biosynthetic enzymes as well as other membrane-associated proteins is crucial for cellular processes such as polar growth and midcell septum formation. We will highlight metabolic enzymes involved in the localized biosynthesis of envelope components such as peptidoglycan, arabinogalactan and outer/inner membrane lipids. The known and potential roles of cytoskeletal and coiled coil proteins in driving subcellular protein localization will also be summarized. Finally, we provide a comprehensive overview of known lateral heterogeneities in mycobacterial plasma membrane, with a particular focus on the intracellular membrane domain, recently revealed by biochemical fractionation and fluorescence microscopy. We consider how this dynamic and multifunctional membrane microdomain contributes to the subcellular localization of membrane proteins and spatially restricted cell envelope biosynthesis in mycobacteria.

PMID: 29762679 [PubMed - indexed for MEDLINE]

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Two Faces of CwlM, an Essential PknB Substrate, in Mycobacterium tuberculosis.

Cell Rep. 2018 Oct 02;25(1):57-67.e5

Authors: Turapov O, Forti F, Kadhim B, Ghisotti D, Sassine J, Straatman-Iwanowska A, Bottrill AR, Moynihan PJ, Wallis R, Barthe P, Cohen-Gonsaud M, Ajuh P, Vollmer W, Mukamolova GV

Abstract
Tuberculosis claims >1 million lives annually, and its causative agent Mycobacterium tuberculosis is a highly successful pathogen. Protein kinase B (PknB) is reported to be critical for mycobacterial growth. Here, we demonstrate that PknB-depleted M. tuberculosis can replicate normally and can synthesize peptidoglycan in an osmoprotective medium. Comparative phosphoproteomics of PknB-producing and PknB-depleted mycobacteria identify CwlM, an essential regulator of peptidoglycan synthesis, as a major PknB substrate. Our complementation studies of a cwlM mutant of M. tuberculosis support CwlM phosphorylation as a likely molecular basis for PknB being essential for mycobacterial growth. We demonstrate that growing mycobacteria produce two forms of CwlM: a non-phosphorylated membrane-associated form and a PknB-phosphorylated cytoplasmic form. Furthermore, we show that the partner proteins for the phosphorylated and non-phosphorylated forms of CwlM are FhaA, a fork head-associated domain protein, and MurJ, a proposed lipid II flippase, respectively. From our results, we propose a model in which CwlM potentially regulates both the biosynthesis of peptidoglycan precursors and their transport across the cytoplasmic membrane.

PMID: 30282038 [PubMed - in process]

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Lipoteichoic acid deficiency permits normal growth but impairs virulence of Streptococcus pneumoniae.

Nat Commun. 2017 12 12;8(1):2093

Authors: Heß N, Waldow F, Kohler TP, Rohde M, Kreikemeyer B, Gómez-Mejia A, Hain T, Schwudke D, Vollmer W, Hammerschmidt S, Gisch N

Abstract
Teichoic acid (TA), a crucial cell wall constituent of the pathobiont Streptococcus pneumoniae, is bound to peptidoglycan (wall teichoic acid, WTA) or to membrane glycolipids (lipoteichoic acid, LTA). Both TA polymers share a common precursor synthesis pathway, but differ in the final transfer of the TA chain to either peptidoglycan or a glycolipid. Here, we show that LTA exhibits a different linkage conformation compared to WTA, and identify TacL (previously known as RafX) as a putative lipoteichoic acid ligase required for LTA assembly. Pneumococcal mutants deficient in TacL lack LTA and show attenuated virulence in mouse models of acute pneumonia and systemic infections, although they grow normally in culture. Hence, LTA is important for S. pneumoniae to establish systemic infections, and TacL represents a potential target for antimicrobial drug development.

PMID: 29233962 [PubMed - indexed for MEDLINE]

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Outer Membrane Translocon Communicates with Inner Membrane ATPase To Stop Lipopolysaccharide Transport.

J Am Chem Soc. 2018 10 10;140(40):12691-12694

Authors: Xie R, Taylor RJ, Kahne D

Abstract
The survival of Gram-negative bacteria depends on assembly of the asymmetric outer membrane, which creates a barrier that prevents entry of toxic molecules including antibiotics. The outer leaflet of the outer membrane is composed of lipopolysaccharide, which is made at the inner membrane and pushed across a protein bridge that spans the inner and outer membranes. We have developed a fluorescent assay to follow lipopolysaccharide (LPS) transport across a bridge linking proteoliposomes that mimic the inner and outer membranes. We show that LPS is delivered to the leaflet of the outer membrane proteoliposome that corresponds to the outer leaflet of the membrane in a cell. Transport stops long before substrates at the inner membrane are exhausted. Using mutants of the transport machinery, we find that the final amount of LPS delivered into the membrane depends on the affinity of the outer membrane translocon for LPS. Furthermore, ATP hydrolysis depends on delivery of LPS into the outer membrane. Therefore, the transport process is regulated by the outer membrane translocon causing ATP hydrolysis in the inner membrane proteoliposome to stop. Negative feedback from the outer membrane to the inner membrane provides a mechanism for long distance control over LPS transport.

PMID: 30253645 [PubMed - indexed for MEDLINE]

When it comes to changing their passwords, bacteria are just as bad as you and me—maybe even worse. A Carnegie Mellon University research team has found that despite 2.7 billion years of evolution, bacteria are still using the same "password" to initiate the process for making spores. Their findings were published in the September issue of PLOS Genetics.

The researchers who made the discovery suggest the signaling may form a sixth sense.

Find could lead to new treatments for obesity, depression

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Bacterial cell wall nanoimaging by autoblinking microscopy.

Sci Rep. 2018 Sep 19;8(1):14038

Authors: Floc'h K, Lacroix F, Barbieri L, Servant P, Galland R, Butler C, Sibarita JB, Bourgeois D, Timmins J

Abstract
Spurious blinking fluorescent spots are often seen in bacteria during single-molecule localization microscopy experiments. Although this 'autoblinking' phenomenon is widespread, its origin remains unclear. In Deinococcus strains, we observed particularly strong autoblinking at the periphery of the bacteria, facilitating its comprehensive characterization. A systematic evaluation of the contributions of different components of the sample environment to autoblinking levels and the in-depth analysis of the photophysical properties of autoblinking molecules indicate that the phenomenon results from transient binding of fluorophores originating mostly from the growth medium to the bacterial cell wall, which produces single-molecule fluorescence through a Point Accumulation for Imaging in Nanoscale Topography (PAINT) mechanism. Our data suggest that the autoblinking molecules preferentially bind to the plasma membrane of bacterial cells. Autoblinking microscopy was used to acquire nanoscale images of live, unlabeled D. radiodurans and could be combined with PALM imaging of PAmCherry-labeled bacteria in two-color experiments. Autoblinking-based super-resolved images provided insight into the formation of septa in dividing bacteria and revealed heterogeneities in the distribution and dynamics of autoblinking molecules within the cell wall.

PMID: 30232348 [PubMed - in process]

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Peptidoglycan in Mycobacteria: chemistry, biology and intervention.

Glycoconj J. 2018 Sep 19;:

Authors: Raghavendra T, Patil S, Mukherjee R

Abstract
Peptidoglycan, a major glycoconjugate in the mycobacterial cell envelope provides strength to resist osmotic stress and plays a pivotal role in maintaining the cellular morphology. Several unique growth stage specific structural alterations occur in its constituent monosaccharides and peptides that allow Mycobacterium to survive nutrient starvation and environmental stress. Here, we discuss the enzymes involved in its intricate biosynthesis that are novel targets for therapeutic intervention and provide an opportunity for potential antibiotic adjuvants. We also revisit the enzymatic steps which are critical for maintaining the equilibrium between peptidoglycan synthesis and hydrolysis during cellular growth and division specifically focused on the importance of cell wall remodelling during "exit from dormancy" in Mycobacterium, a phenomenon with tremendous physiological and therapeutic importance for intervention in mycobacterial infections.

PMID: 30232572 [PubMed - as supplied by publisher]

Bacterial Strategies to Preserve Cell Wall Integrity Against Environmental Threats.

Front Microbiol. 2018;9:2064

Authors: Yadav AK, Espaillat A, Cava F

Abstract
Bacterial cells are surrounded by an exoskeleton-like structure, the cell wall, composed primarily of the peptidoglycan (PG) sacculus. This structure is made up of glycan strands cross-linked by short peptides generating a covalent mesh that shapes bacteria and prevents their lysis due to their high internal osmotic pressure. Even though the PG is virtually universal in bacteria, there is a notable degree of diversity in its chemical structure. Modifications in both the sugars and peptides are known to be instrumental for bacteria to cope with diverse environmental challenges. In this review, we summarize and discuss the cell wall strategies to withstand biotic and abiotic environmental insults such as the effect of antibiotics targeting cell wall enzymes, predatory PG hydrolytic proteins, and PG signaling systems. Finally we will discuss the opportunities that species-specific PG variability might open to develop antimicrobial therapies.

PMID: 30233540 [PubMed]

The Fluorescent D-Amino Acid NADA as a Tool to Study the Conditional Activity of Transpeptidases in Escherichia coli.

Front Microbiol. 2018;9:2101

Authors: Montón Silva A, Otten C, Biboy J, Breukink E, VanNieuwenhze M, Vollmer W, den Blaauwen T

Abstract
The enzymes responsible for the synthesis of the peptidoglycan (PG) layer constitute a fundamental target for a large group of antibiotics. The family of β-lactam antibiotics inhibits the DD-transpeptidase (TPase) activity of the penicillin binding proteins (PBPs), whereas its subgroup of carbapenems can also block the TPase activity of the LD-TPases. D-Ala fluorescent probes, such as NADA, are incorporated into the PG presumably by TPases in Escherichia coli and can be used to study conditions that are required for their function. Of all LD-TPases of E. coli, only LdtD was able to incorporate NADA during exponential growth. Overproduction of LdtD caused NADA to be especially inserted at mid cell in the presence of LpoB-activated PBP1b and the class C PBP5. Using the NADA assay, we could confirm that LpoB activates PBP1b at mid cell and that CpoB regulates the activity of PBP1b in vivo. Overproduction of LdtD was able to partly compensate for the inhibition of the cell division specific class B PBP3 by aztreonam. We showed that class A PBP1c and the class C PBP6b cooperated with LdtD for NADA incorporation when PBP1b and PBP5 were absent, respectively. Besides, we proved that LdtD is active at pH 7.0 whereas LdtE and LdtF are more active in cells growing at pH 5.0 and they seem to cooperate synergistically. The NADA assay proved to be a useful tool for the analysis of the in vivo activities of the proteins involved in PG synthesis and our results provide additional evidence that the LD-TPases are involved in PG maintenance at different conditions.

PMID: 30233559 [PubMed]

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Metabolic Labeling of Pseudaminic Acid-containing Glycans on Bacterial Surfaces.

ACS Chem Biol. 2018 Sep 19;:

Authors: Andolina G, Wei R, Liu H, Zhang Q, Yang X, Cao H, Chen S, Yan A, Li XD, Li X

Abstract
The rise in antibiotic resistant bacteria is causing worldwide concerns. The urgent need for new antibacterial drugs calls for new thinking and strategies to explore novel, narrow-spectrum and pathogen-specific antibacterial targets. Legionaminic acid (Leg) and pseudaminic acid (Pse) are nonulosonic acid carbohydrates with structural similarity to eukaryotic sialic acid, and are distributed in numerous pathogenic Gram-negative bacteria as components of cell surface-associated glycans. They are involved in the host interaction, pathogenicity, anti-phage defense mechanism and immune escape mechanism. To further explore their biological significance, we developed a synthesis of 2-acetamido-4-azidoacetamido-2,4,6-trideoxy-L-altrose (Alt-4NAz) and 2-azidoacetamido-4-acetamido-2,4,6-trideoxy-L-altrose (Alt-2NAz), among which Alt-4NAz served as an effective chemical reporter to realize bacterial Pse metabolic labeling. The effectiveness of this chemical reporter has been demonstrated in Pseudomonas aeruginosa, Vibrio vulnificus and Acinetobacter baumannii strains. Expectedly, this strategy can provide a useful assay to detect phenotypic presence of Pse biosynthesis and screen for agents targeting this pathway.

PMID: 30230814 [PubMed - as supplied by publisher]

A recent study by a team of researchers at the University of Georgia provides insight into how and why bacteria become resistant to commonly used antibiotics over time.

A rogue pharmaceutical company ramped up the cost of a common antibiotic by 400 percent. While the medical community is irate, could high prices make antibiotics worth investing in?

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Novel Inhibitor Discovery of Staphylococcus aureus Sortase B and the Mechanism Confirmation via Molecular Modeling.

Molecules. 2018 Apr 23;23(4):

Authors: Wang G, Wang X, Sun L, Gao Y, Niu X, Wang H

Abstract
SortaseB (SrtB) plays a critical role in Staphylococcus aureus (S. aureus) infections. According to the reports in the literature, SrtB can anchor the IsdC to the cell wall to capture iron from the host to achieve a successful invasion. On the other hand, SrtB could also affect the adhesion of S. aureus to host cells based on previous studies. Here, we report about a novel SrtB inhibitor, coptisine, a natural compound that does not exhibit antibacterial activity but can inhibit the SrtB activity in vitro. A cytotoxicity test indicated that coptisine protects human lung epithelial cells from S. aureus. In addition, coptisine can reduce the adhesion of S. aureus to human lung epithelial cells based on the result of plate colony counting assay. Molecular dynamics simulation revealed that coptisine can bind to the active pocket of SrtB, leading to its activity loss. Through the calculation of binding free energy between ligand and protein, site-directed mutagenesis and fluorescence spectroscopy quenching methods, it was confirmed that residues of Arg115, Asn116, and Ile182 played a vital role in the interaction of SrtB with coptisine. These data provide the theoretical basis for the therapy option to the infections caused by S. aureus.

PMID: 29690584 [PubMed - indexed for MEDLINE]

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Enzyme targets for drug design of new anti-virulence therapeutics.

Curr Opin Struct Biol. 2018 Sep 14;53:140-150

Authors: Kahler CM, Sarkar-Tyson M, Kibble EA, Stubbs KA, Vrielink A

Abstract
Society has benefitted greatly from the use of antibiotics. Unfortunately, the misuse of these valuable molecules has resulted in increased levels of antibiotic resistance, a major global and public health issue. This resistance and the reliance on a small number of biological targets for the development of antibiotics emphasizes the need for new targets. A critical aspect guiding the development of new antimicrobials through a rational structure-guided approach is to understand the molecular structures of specific biological targets of interest. Here we give an overview of the structures of bacterial virulence enzyme targets involved in protein folding, peptidoglycan biosynthesis and cell wall modification. These include enzymes of the thiol-disulphide oxidoreductase pathway (DSB enzymes), peptidyl-proly cis/trans isomerases (Mips), enzymes from the Mur pathway and enzymes involved in lipopolysaccharide modification (EptA and ArnT). We also present progress towards inhibitor design of these targets for the development of novel anti-virulence therapeutic agents.

PMID: 30223251 [PubMed - as supplied by publisher]

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Interplay between Peptidoglycan Biology and Virulence in Gram-Negative Pathogens.

Microbiol Mol Biol Rev. 2018 Dec;82(4):

Authors: Juan C, Torrens G, Barceló IM, Oliver A

Abstract
SUMMARYThe clinical and epidemiological threat of the growing antimicrobial resistance in Gram-negative pathogens, particularly for β-lactams, the most frequently used and relevant antibiotics, urges research to find new therapeutic weapons to combat the infections caused by these microorganisms. An essential previous step in the development of these therapeutic solutions is to identify their potential targets in the biology of the pathogen. This is precisely what we sought to do in this review specifically regarding the barely exploited field analyzing the interplay among the biology of the peptidoglycan and related processes, such as β-lactamase regulation and virulence. Hence, here we gather, analyze, and integrate the knowledge derived from published works that provide information on the topic, starting with those dealing with the historically neglected essential role of the Gram-negative peptidoglycan in virulence, including structural, biogenesis, remodeling, and recycling aspects, in addition to proinflammatory and other interactions with the host. We also review the complex link between intrinsic β-lactamase production and peptidoglycan metabolism, as well as the biological costs potentially associated with the expression of horizontally acquired β-lactamases. Finally, we analyze the existing evidence from multiple perspectives to provide useful clues for identifying targets enabling the future development of therapeutic options attacking the peptidoglycan-virulence interconnection as a key weak point of the Gram-negative pathogens to be used, if not to kill the bacteria, to mitigate their capacity to produce severe infections.

PMID: 30209071 [PubMed - in process]

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Probing key elements of teixobactin-lipid II interactions in membranes.

Chem Sci. 2018 Sep 14;9(34):6997-7008

Authors: Wen PC, Vanegas JM, Rempe SB, Tajkhorshid E

Abstract
Teixobactin (Txb) is a recently discovered antibiotic against Gram-positive bacteria that induces no detectable resistance. The bactericidal mechanism is believed to be the inhibition of cell wall biosynthesis by Txb binding to lipid II and lipid III. Txb binding specificity likely arises from targeting of the shared lipid component, the pyrophosphate moiety. Despite synthesis and functional assessment of numerous chemical analogs of Txb, and consequent identification of the Txb pharmacophore, the detailed structural information of Txb-substrate binding is still lacking. Here, we use molecular modeling and microsecond-scale molecular dynamics simulations to capture the formation of Txb-lipid II complexes at a membrane surface. Two dominant binding conformations were observed, both showing characteristic lipid II phosphate binding by the Txb backbone amides near the C-terminal cyclodepsipeptide (d-Thr8-Ile11) ring. Additionally, binding by Txb also involved the side chain hydroxyl group of Ser7, as well as a secondary phosphate binding provided by the side chain of l-allo-enduracididine. Interestingly, those conformations differ by swapping two groups of hydrogen bond donors that coordinate the two phosphate moieties of lipid II, resulting in opposite orientations of lipid II binding. In addition, residues d-allo-Ile5 and Ile6 serve as the membrane anchors in both Txb conformations, regardless of the detailed phosphate binding interactions near the cyclodepsipeptide ring. The role of hydrophobic residues in Txb activity is primarily for its membrane insertion, and subsidiarily to provide non-polar interactions with the lipid II tail. Based on the Txb-lipid II interactions captured in their complexes, as well as their partitioning depths into the membrane, we propose that the bactericidal mechanism of Txb is to arrest cell wall synthesis by selectively inhibiting the transglycosylation of peptidoglycan, while possibly leaving the transpeptidation step unaffected. The observed "pyrophosphate caging" mechanism of lipid II inhibition appears to be similar to some lantibiotics, but different from that of vancomycin or bacitracin.

PMID: 30210775 [PubMed]

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The serine/threonine kinase Stk and the phosphatase Stp regulate cell wall synthesis in Staphylococcus aureus.

Sci Rep. 2018 Sep 12;8(1):13693

Authors: Jarick M, Bertsche U, Stahl M, Schultz D, Methling K, Lalk M, Stigloher C, Steger M, Schlosser A, Ohlsen K

Abstract
The cell wall synthesis pathway producing peptidoglycan is a highly coordinated and tightly regulated process. Although the major components of bacterial cell walls have been known for decades, the complex regulatory network controlling peptidoglycan synthesis and many details of the cell division machinery are not well understood. The eukaryotic-like serine/threonine kinase Stk and the cognate phosphatase Stp play an important role in cell wall biosynthesis and drug resistance in S. aureus. We show that stp deletion has a pronounced impact on cell wall synthesis. Deletion of stp leads to a thicker cell wall and decreases susceptibility to lysostaphin. Stationary phase Δstp cells accumulate peptidoglycan precursors and incorporate higher amounts of incomplete muropeptides with non-glycine, monoglycine and monoalanine interpeptide bridges into the cell wall. In line with this cell wall phenotype, we demonstrate that the lipid II:glycine glycyltransferase FemX can be phosphorylated by the Ser/Thr kinase Stk in vitro. Mass spectrometric analyses identify Thr32, Thr36 and Ser415 as phosphoacceptors. The cognate phosphatase Stp dephosphorylates these phosphorylation sites. Moreover, Stk interacts with FemA and FemB, but is unable to phosphorylate them. Our data indicate that Stk and Stp modulate cell wall synthesis and cell division at several levels.

PMID: 30209409 [PubMed - in process]

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Mechanical Genomic Studies Reveal the Role of d-Alanine Metabolism in Pseudomonas aeruginosa Cell Stiffness.

MBio. 2018 Sep 11;9(5):

Authors: Trivedi RR, Crooks JA, Auer GK, Pendry J, Foik IP, Siryaporn A, Abbott NL, Gitai Z, Weibel DB

Abstract
The stiffness of bacteria prevents cells from bursting due to the large osmotic pressure across the cell wall. Many successful antibiotic chemotherapies target elements that alter mechanical properties of bacteria, and yet a global view of the biochemistry underlying the regulation of bacterial cell stiffness is still emerging. This connection is particularly interesting in opportunistic human pathogens such as Pseudomonas aeruginosa that have a large (80%) proportion of genes of unknown function and low susceptibility to different families of antibiotics, including beta-lactams, aminoglycosides, and quinolones. We used a high-throughput technique to study a library of 5,790 loss-of-function mutants covering ~80% of the nonessential genes and correlated P. aeruginosa individual genes with cell stiffness. We identified 42 genes coding for proteins with diverse functions that, when deleted individually, decreased cell stiffness by >20%. This approach enabled us to construct a "mechanical genome" for P. aeruginosa d-Alanine dehydrogenase (DadA) is an enzyme that converts d-Ala to pyruvate that was included among the hits; when DadA was deleted, cell stiffness decreased by 18% (using multiple assays to measure mechanics). An increase in the concentration of d-Ala in cells downregulated the expression of genes in peptidoglycan (PG) biosynthesis, including the peptidoglycan-cross-linking transpeptidase genes ponA and dacC Consistent with this observation, ultraperformance liquid chromatography-mass spectrometry analysis of murein from P. aeruginosa cells revealed that dadA deletion mutants contained PG with reduced cross-linking and altered composition compared to wild-type cells.IMPORTANCE The mechanical properties of bacteria are important for protecting cells against physical stress. The cell wall is the best-characterized cellular element contributing to bacterial cell mechanics; however, the biochemistry underlying its regulation and assembly is still not completely understood. Using a unique high-throughput biophysical assay, we identified genes coding proteins that modulate cell stiffness in the opportunistic human pathogen Pseudomonas aeruginosa This approach enabled us to discover proteins with roles in a diverse range of biochemical pathways that influence the stiffness of P. aeruginosa cells. We demonstrate that d-Ala-a component of the peptidoglycan-is tightly regulated in cells and that its accumulation reduces expression of machinery that cross-links this material and decreases cell stiffness. This research demonstrates that there is much to learn about mechanical regulation in bacteria, and these studies revealed new nonessential P. aeruginosa targets that may enhance antibacterial chemotherapies or lead to new approaches.

PMID: 30206169 [PubMed - in process]

Clostridium difficile causes infections that are hard to treat and that may have negative outcomes for health. What lends this bacterium its resilience?