The metabolic enzyme ManA reveals a link between cell wall integrity and chromosome morphology

Universal receptive system as a novel regulator of transcriptomic activity of Staphylococcus aureus

Our previous studies revealed the existence of a Universal Receptive System that regulates interactions between cells and their environment. This system is composed of DNA- and RNA-based Teazeled receptors (TezRs) found on the surface of prokaryotic and eukaryotic cells, as well as integrases and recombinases. In the current study, we aimed to provide further insight into the regulatory role of TezR and its loss in Staphylococcus aureus gene transcription. To this end, transcriptomic analysis of S. aureus MSSA VT209 was performed following the destruction of TezRs. Bacterial RNA samples were extracted from nuclease-treated and untreated S. aureus MSSA VT209. After destruction of the DNA-based-, RNA-, or combined DNA- and RNA-based TezRs of S. aureus, 103, 150, and 93 genes were significantly differently expressed, respectively. The analysis revealed differential clustering of gene expression following the loss of different TezRs, highlighting individual cellular responses following the loss of DNA- and RNA-based TezRs. KEGG pathway gene enrichment analysis revealed that the most upregulated pathways following TezR inactivation included those related to energy metabolism, cell wall metabolism, and secretion systems. Some of the genetic pathways were related to the inhibition of biofilm formation and increased antibiotic resistance, and we confirmed this at the phenotypic level using in vitro studies. The results of this study add another line of evidence that the Universal Receptive System plays an important role in cell regulation, including cell responses to the environmental factors of clinically important pathogens, and that nucleic acid-based TezRs are functionally active parts of the extrabiome.

Universal Receptive System as a novel regulator of transcriptomic activity of Staphylococcus aureus

Our previous studies revealed the existence of a Universal Receptive System that regulates interactions between cells and their environment. This system is composed of DNA- and RNA-based Teazeled receptors (TezRs) found on the surface of prokaryotic and eukaryotic cells, as well as integrases and recombinases.. In the current study, we aimed to provide further insight into the regulatory role of TezR and its loss in Staphylococcus aureus gene transcription. To this end, transcriptomic analysis of S. aureus MSSA VT209 was performed following the destruction of TezRs. Bacterial RNA samples were extracted from nuclease-treated and untreated S. aureus MSSA VT209. After destruction of the DNA-based-, RNA-, or combined DNA- and RNA-based TezRs of S. aureus , 103, 150, and 93 genes were significantly differently expressed, respectively. The analysis revealed differential clustering of gene expression following the loss of different TezRs, highlighting individual cellular responses following the loss of DNA- and RNA-based TezRs. KEGG pathway gene enrichment analysis revealed that the most upregulated pathways following TezR inactivation included those related to energy metabolism, cell wall metabolism, and secretion systems. Some of the genetic pathways were related to the inhibition of biofilm formation and increased antibiotic resistance, and we confirmed this at the phenotypic level using in vitro studies. The results of this study add another line of evidence that the Universal Receptive System plays an important role in cell regulation, including cell responses to the environmental factors of clinically important pathogens, and that nucleic acid-based TezRs are functionally active parts of the extrabiome.

Bacillus subtilis forms twisted cells with cell wall integrity defects upon removal of the molecular chaperones DnaK and trigger factor

The protein homeostasis network ensures a proper balance between synthesis, folding, and degradation of all cellular proteins. DnaK and trigger factor (TF) are ubiquitous bacterial molecular chaperones that assist in protein folding, as well as preventing protein misfolding and aggregation. In Escherichia coli, DnaK and TF possess partially overlapping functions. Their combined depletion results in proteostasis collapse and is synthetically lethal at temperatures above 30°C. To increase our understanding on how proteostasis is maintained in Gram-positive bacteria, we have investigated the physiological effects of deleting dnaK and tig (encoding for DnaK and TF) in Bacillus subtilis. We show that combined deletion of dnaK and tig in B. subtilis is non-lethal, but causes a severe pleiotropic phenotype, including an aberrant twisted and filamentous cell morphology, as well as decreased tolerance to heat and to cell wall active antibiotics and hydrolytic enzymes, indicative of defects in cell wall integrity. In addition, cells lacking DnaK and TF have a much smaller colony size due to defects in motility. Despite these physiological changes, we observed no major compromises in important cellular processes such as cell growth, FtsZ localization and division and only moderate defects in spore formation. Finally, through suppressor analyses, we found that the wild-type cell shape can be partially restored by mutations in genes involved in metabolism or in other diverse cellular processes.

Sugar-Phosphate Toxicities

Accumulation of phosphorylated intermediates during cellular metabolism can have wide-ranging toxic effects on many organisms, including humans and the pathogens that infect them. These toxicities can be induced by feeding an upstream metabolite (a sugar, for instance) while simultaneously blocking the appropriate metabolic pathway with either a mutation or an enzyme inhibitor. Here, we survey the toxicities that can arise in the metabolism of glucose, galactose, fructose, fructose-asparagine, glycerol, trehalose, maltose, mannose, mannitol, arabinose, and rhamnose. Select enzymes in these metabolic pathways may serve as novel therapeutic targets. Some are conserved broadly among prokaryotes and eukaryotes (e.g., glucose and galactose) and are therefore unlikely to be viable drug targets. However, others are found only in bacteria (e.g., fructose-asparagine, rhamnose, and arabinose), and one is found in fungi but not in humans (trehalose). We discuss what is known about the mechanisms of toxicity and how resistance is achieved in order to identify the prospects and challenges associated with targeted exploitation of these pervasive metabolic vulnerabilities.

Aflatoxin B1 Induces Gut-Inflammation-Associated Fecal Lipidome Changes in F344 Rats

Aflatoxin B1 (AFB1) induced intestinal epithelial damage in rodent models, which indicates that long-term exposure to AFB1 may cause chronic gut disorders. In this study we tested the hypothesis that AFB1-induced adverse effects on gut is mediated by gut-microbiota, which is partially reflected by the changes of fecal microbiome and metabolome. F344 rats were orally exposed to AFB1 of 0, 5, 25 and 75 µg kg-1 body weight for 4 weeks and fecal samples were collected. An ion-fragmentation-spectrum-based metabolomics approach was developed to investigate the fecal microbiota-associated metabolic changes in fecal samples. We found that AFB1 inhibited the hepatic and intestinal metabolism of bile constituents. As compared to the controls, bile acid synthesis-associated cholesterols in rats treated with 25 µg kg-1 (the middle-dose group) were significantly decreased in the fecal samples, e.g., lathosterol (45% reduction), cholesterol ester (21% reduction), chenodeoxycholic acid (20% reduction), dihydroxycholesterol (55% reduction), hydroxycholesterol (20% reduction), and 5-cholestene (29% reduction). While disease-associated lipids were not detectable in the feces of the control group, they were found in AFB1-treated groups, including diglyceride, monoacylglyceride, 19,20-dihydroxy-docosapentaenoic acid, and phosphatidylethanolamine. Metabolisms of carbohydrates and production of short chain fatty acids were remarkedly decreased in all treated groups. Moreover, an inflammatory-bowel-disease (IBD)-associated taxonomic structure of fecal microbiota was observed as ∼25% Lachnospiraceae, ∼25% Ruminococcaceae, < 1% Lactobacillales, which was similar to the composition pattern found in IBD patients. These results suggest that AFB1-induced disruption on gut-microbiota, partially reflected by fecal microbiome and metabolome, may play important roles in the pathogenesis of chronic gut disorders.

Metabolic Control of Cell Elongation and Cell Division in Bacillus subtilis

To survive and adapt to changing nutritional conditions, bacteria must rapidly modulate cell cycle processes, such as doubling time or cell size. Recent data have revealed that cellular metabolism is a central regulator of bacterial cell cycle. Indeed, proteins that can sense precursors or metabolites or enzymes, in addition to their enzymatic activities involved in metabolism, were shown to directly control cell cycle processes in response to changes in nutrient levels. Here we focus on cell elongation and cell division in the Gram-positive rod-shaped bacterium Bacillus subtilis and we report evidences linking these two cellular processes to environmental nutritional availability and thus metabolic cellular status.

Disruption of the MreB Elongasome Is Overcome by Mutations in the Tricarboxylic Acid Cycle

The bacterial actin homolog, MreB, is highly conserved among rod-shaped bacteria and essential for growth under normal growth conditions. MreB directs the localization of cell wall synthesis and loss of MreB results in round cells and death. Using the MreB depolymerizing drug, A22, we show that changes to central metabolism through deletion of malate dehydrogenase from the tricarboxylic acid (TCA) cycle results in cells with an increased tolerance to A22. We hypothesize that deletion of malate dehydrogenase leads to the upregulation of gluconeogenesis resulting in an increase in cell wall precursors. Consistent with this idea, metabolite analysis revealed that malate dehydrogenase (mdh) deletion cells possess elevated levels of several glycolysis/gluconeogenesis compounds and the cell wall precursor, uridine diphosphate N-acetylglucosamine (UDP-NAG). In agreement with these results, the increased A22 resistance phenotype can be recapitulated through the addition of glucose to the media. Finally, we show that this increase in antibiotic tolerance is not specific to A22 but also applies to the cell wall-targeting antibiotic, mecillinam.

Effects of fixation on bacterial cellular dimensions and integrity

Fixation facilitates imaging of subcellular localization and cell morphology, yet it remains unknown how fixation affects cellular dimensions and intracellular fluorescence patterns, particularly during long-term storage. Here, we characterized the effects of multiple fixatives on several bacterial species. Fixation generally reduced cell length by 5-15%; single-cell tracking in microfluidics revealed that the length decrease was an aggregate effect of many steps in the fixation protocol and that fluorescence of cytoplasmic GFP but not membrane-bound MreB-msfGFP was rapidly lost with formaldehyde-based fixatives. Cellular dimensions were preserved in formaldehyde-based fixatives for ≥4 days, but methanol caused length to decrease. Although methanol preserved cytoplasmic fluorescence better than formaldehyde-based fixatives, some Escherichia coli cells were able to grow directly after fixation. Moreover, methanol fixation caused lysis in a subpopulation of cells, with virtually all Bacillus subtilis cells lysing after one day. These findings highlight tradeoffs between maintenance of fluorescence and membrane integrity for future applications of fixation.

Sugar-Phosphate Metabolism Regulates Stationary-Phase Entry and Stalk Elongation in Caulobacter crescentus

Bacteria have a variety of mechanisms for adapting to environmental perturbations. Changes in oxygen availability result in a switch between aerobic and anaerobic respiration, whereas iron limitation may lead to siderophore secretion. In addition to metabolic adaptations, many organisms respond by altering their cell shape. Caulobacter crescentus, when grown under phosphate-limiting conditions, dramatically elongates its polar stalk appendage. The stalk is hypothesized to facilitate phosphate uptake; however, the mechanistic details of stalk synthesis are not well characterized. We used a chemical mutagenesis approach to isolate and characterize stalk-deficient mutants, one of which had two mutations in the phosphomannose isomerase gene (manA) that were necessary and sufficient to inhibit stalk elongation. Transcription of the pho regulon was unaffected in the manA mutant; therefore, ManA plays a unique regulatory role in stalk synthesis. The mutant ManA had reduced enzymatic activity, resulting in a 5-fold increase in the intracellular fructose 6-phosphate/mannose 6-phosphate ratio. This metabolic imbalance impaired the synthesis of cellular envelope components derived from mannose 6-phosphate, namely, lipopolysaccharide O-antigen and exopolysaccharide. Furthermore, the manA mutations prevented C. crescentus cells from efficiently entering stationary phase. Deletion of the stationary-phase response regulator gene spdR inhibited stalk elongation in wild-type cells, while overproduction of the alarmone ppGpp, which triggers growth arrest and stationary-phase entry, increased stalk length in the manA mutant strain. These results demonstrate that sugar-phosphate metabolism regulates stalk elongation independently of phosphate starvation.IMPORTANCE Metabolic control of bacterial cell shape is an important mechanism for adapting to environmental perturbations. Caulobacter crescentus dramatically elongates its polar stalk appendage in response to phosphate starvation. To investigate the mechanism of this morphological adaptation, we isolated stalk-deficient mutants, one of which had mutations in the phosphomannose isomerase gene (manA) that blocked stalk elongation, despite normal activation of the phosphate starvation response. The mutant ManA resulted in an imbalance in sugar-phosphate concentrations, which had effects on the synthesis of cellular envelope components and entry into stationary phase. Due to the interconnectivity of metabolic pathways, our findings may suggest more generally that the modulation of bacterial cell shape involves the regulation of growth phase and the synthesis of cellular building blocks.

Pdh is involved in the cell division and Normal septation of Streptococcus suis

Streptococcus suis (S. suis) is an important zoonotic pathogen that causes major economic losses in the pig industry worldwide. The S. suis cell division process is an integral part of its growth and reproduction, which is controlled by a complex regulatory network. Pyruvate dehydrogenase (PDH), which catalyzes the oxidative decarboxylation of pyruvate to form acetyl-CoA, while reducing NAD + to NADH, plays an important role in energy metabolism. Recently, we reported that pdh regulates virulence by reducing stress tolerance and biofilm formation in S. suis serotype 2. In this study, we found that deletion of the pdh gene in S. suis resulted in abnormal cell chains, plump morphology and abnormal localization of the Z rings, indicating that the knockout mutant is impaired in its ability to divide. In addition, the interaction between FtsZ and PDH in vitro was confirmed by ELISA, and qRT-PCR analysis revealed that the deletion of the pdh gene results in differential expression of the division-related genes ftsZ, ftsK, ftsl, zapA, divIC, pbp1a, rodA, mreD, and sepF. These results indicate that pdh is involved in the normal formation of Z rings and cell morphology during S. suis cell division.

Phosphosugar Stress in Bacillus subtilis: Intracellular Accumulation of Mannose 6-Phosphate Derepressed the glcR-phoC Operon from Repression by GlcR

Bacillus subtilis phosphorylates sugars during or after their transport into the cell. Perturbation in the conversion of intracellular phosphosugars to the central carbon metabolites and accumulation of phosphosugars can impose stress on the cells. In this study, we investigated the effect of phosphosugar stress on B. subtilis Preliminary experiments indicated that the nonmetabolizable analogs of glucose were unable to impose stress on B. subtilis In contrast, deletion of manA encoding mannose 6-phosphate isomerase (responsible for conversion of mannose 6-phosphate to fructose 6-phosphate) resulted in growth arrest and bulged cell shape in the medium containing mannose. Besides, an operon encoding a repressor (GlcR) and a haloic acid dehalogenase (HAD)-like phosphatase (PhoC; previously YwpJ) were upregulated. Integration of the P _glcR-lacZ cassette into different mutational backgrounds indicated that P _glcR is induced when (i) a manA-deficient strain is cultured with mannose or (ii) when glcR is deleted. GlcR repressed the transcription of glcR-phoC by binding to the σ^A-type core elements of P _glcR An electrophoretic mobility shift assay showed no interaction between mannose 6-phosphate (or other phosphosugars) and the GlcR-P _glcR DNA complex. PhoC was an acid phosphatase mainly able to dephosphorylate glycerol 3-phosphate and ribose 5-phosphate. Mannose 6-phosphate was only weakly dephosphorylated by PhoC. Since deletion of glcR and phoC alone or in combination had no effect on the cells during phosphosugar stress, it is assumed that the derepression of glcR-phoC is a side effect of phosphosugar stress in B. subtilis IMPORTANCE Bacillus subtilis has different stress response systems to cope with external and internal stressors. Here, we investigated how B. subtilis deals with the high intracellular concentration of phosphosugars as an internal stressor. The results indicated the derepression of an operon consisting of a repressor (GlcR) and a phosphatase (PhoC). Further analysis revealed that this operon is not a phosphosugar stress response system. The substrate specificity of PhoC may indicate a connection between the glcR-phoC operon and pathways in which glycerol 3-phosphate and ribose 5-phosphate are utilized, such as membrane biosynthesis and teichoic acid elongation.

Tunicamycin Mediated Inhibition of Wall Teichoic Acid Affects Staphylococcus aureus and Listeria monocytogenes Cell Morphology, Biofilm Formation and Virulence

The emergence of bacterial resistance to therapeutic antibiotics limits options for treatment of common microbial diseases. Subinhibitory antibiotics dosing, often aid in the emergence of resistance, but its impact on pathogen's physiology and pathogenesis is not well understood. Here we investigated the effect of tunicamycin, a cell wall teichoic acid (WTA) biosynthesis inhibiting antibiotic at the subinhibitory dosage on Staphylococcus aureus and Listeria monocytogenes physiology, antibiotic cross-resistance, biofilm-formation, and virulence. Minimum inhibitory concentration (MIC) of tunicamycin to S. aureus and L. monocytogenes was 20-40 μg/ml and 2.5-5 μg/ml, respectively, and the subinhibitory concentration was 2.5-5 μg/ml and 0.31-0.62 μg/ml, respectively. Tunicamycin pre-exposure reduced cellular WTA levels by 18-20% and affected bacterial cell wall ultrastructure, cell membrane permeability, morphology, laser-induced colony scatter signature, and bacterial ability to form biofilms. It also induced a moderate level of cross-resistance to tetracycline, ampicillin, erythromycin, and meropenem for S. aureus, and ampicillin, erythromycin, vancomycin, and meropenem for L. monocytogenes. Pre-treatment of bacterial cells with subinhibitory concentrations of tunicamycin also significantly reduced bacterial adhesion to and invasion into an enterocyte-like Caco-2 cell line, which is supported by reduced expression of key virulence factors, Internalin B (InlB) and Listeria adhesion protein (LAP) in L. monocytogenes, and a S. aureus surface protein A (SasA) in S. aureus. Tunicamycin-treated bacteria or the bacterial WTA preparation suppressed NF-κB and inflammatory cytokine production (TNFα, and IL-6) from murine macrophage cell line (RAW 264.7) indicating the reduced WTA level possibly attenuates an inflammatory response. These results suggest that at the subinhibitory dosage, tunicamycin-mediated inhibition of WTA biosynthesis interferes with cell wall structure, pathogens infectivity and inflammatory response, and ability to form biofilms but promotes the development of antibiotic cross-resistance.

A new class of synthetic retinoid antibiotics effective against bacterial persisters

A challenge in the treatment of Staphylococcus aureus infections is the high prevalence of methicillin-resistant S. aureus (MRSA) strains and the formation of non-growing, dormant 'persister' subpopulations that exhibit high levels of tolerance to antibiotics and have a role in chronic or recurrent infections. As conventional antibiotics are not effective in the treatment of infections caused by such bacteria, novel antibacterial therapeutics are urgently required. Here we used a Caenorhabditis elegans-MRSA infection screen to identify two synthetic retinoids, CD437 and CD1530, which kill both growing and persister MRSA cells by disrupting lipid bilayers. CD437 and CD1530 exhibit high killing rates, synergism with gentamicin, and a low probability of resistance selection. All-atom molecular dynamics simulations demonstrated that the ability of retinoids to penetrate and embed in lipid bilayers correlates with their bactericidal ability. An analogue of CD437 was found to retain anti-persister activity and show an improved cytotoxicity profile. Both CD437 and this analogue, alone or in combination with gentamicin, exhibit considerable efficacy in a mouse model of chronic MRSA infection. With further development and optimization, synthetic retinoids have the potential to become a new class of antimicrobials for the treatment of Gram-positive bacterial infections that are currently difficult to cure.

Thinking big: the tunability of bacterial cell size

The determination of cell size is a fundamental challenge for all living organisms. In a given growth condition, cell size for a particular bacterial species typically falls within a narrow distribution. Nonetheless, size can vary enormously across species, and the size of a single bacterium can even vary substantially across growth conditions. Recent phenomenological studies have revived classic interest in how cells maintain their size and how they adjust their size with changes in growth rate. However, the mechanisms by which cells establish a particular size are relatively enigmatic. Here, we review existing knowledge on how size in rod-shaped bacteria is shaped by nutrient, mechanical, and genetic factors. We also examine obstacles to accurate size measurement and recent technologies that help to overcome these hurdles. Finally, we discuss the relevance of cell size to bacterial physiology.

Crosstalk between the tricarboxylic acid cycle and peptidoglycan synthesis in Caulobacter crescentus through the homeostatic control of α-ketoglutarate

To achieve robust replication, bacteria must integrate cellular metabolism and cell wall growth. While these two processes have been well characterized, the nature and extent of cross-regulation between them is not well understood. Here, using classical genetics, CRISPRi, metabolomics, transcriptomics and chemical complementation approaches, we show that a loss of the master regulator Hfq in Caulobacter crescentus alters central metabolism and results in cell shape defects in a nutrient-dependent manner. We demonstrate that the cell morphology phenotype in the hfq deletion mutant is attributable to a disruption of α-ketoglutarate (KG) homeostasis. In addition to serving as a key intermediate of the tricarboxylic acid (TCA) cycle, KG is a by-product of an enzymatic reaction required for the synthesis of peptidoglycan, a major component of the bacterial cell wall. Accumulation of KG in the hfq deletion mutant interferes with peptidoglycan synthesis, resulting in cell morphology defects and increased susceptibility to peptidoglycan-targeting antibiotics. This work thus reveals a direct crosstalk between the TCA cycle and cell wall morphogenesis. This crosstalk highlights the importance of metabolic homeostasis in not only ensuring adequate availability of biosynthetic precursors, but also in preventing interference with cellular processes in which these intermediates arise as by-products.

Metabolism Shapes the Cell

More than 5 decades of work support the idea that cell envelope synthesis, including the inward growth of cell division, is tightly coordinated with DNA replication and protein synthesis through central metabolism. Remarkably, no unifying model exists to account for how these fundamentally disparate processes are functionally coupled. Recent studies demonstrate that proteins involved in carbohydrate and nitrogen metabolism can moonlight as direct regulators of cell division, coordinate cell division and DNA replication, and even suppress defects in DNA replication. In this minireview, we focus on studies illustrating the intimate link between metabolism and regulation of peptidoglycan (PG) synthesis during growth and division, and we identify the following three recurring themes. (i) Nutrient availability, not growth rate, is the primary determinant of cell size. (ii) The degree of gluconeogenic flux is likely to have a profound impact on the metabolites available for cell envelope synthesis, so growth medium selection is a critical consideration when designing and interpreting experiments related to morphogenesis. (iii) Perturbations in pathways relying on commonly shared and limiting metabolites, like undecaprenyl phosphate (Und-P), can lead to pleotropic phenotypes in unrelated pathways.

Toxin-Antitoxin systems eliminate defective cells and preserve symmetry in Bacillus subtilis biofilms

Toxin-antitoxin modules are gene pairs encoding a toxin and its antitoxin, and are found on the chromosomes of many bacteria, including pathogens. Here, we characterize the specific contribution of the TxpA and YqcG toxins in elimination of defective cells from developing Bacillus subtilis biofilms. On nutrient limitation, defective cells accumulated in the biofilm breaking its symmetry. Deletion of the toxins resulted in accumulation of morphologically abnormal cells, and interfered with the proper development of the multicellular community. Dual physiological responses are of significance for TxpA and YqcG activation: nitrogen deprivation enhances the transcription of both TxpA and YqcG toxins, and simultaneously sensitizes the biofilm cells to their activity. Furthermore, we demonstrate that while both toxins when overexpressed affect the morphology of the developing biofilm, the toxin TxpA can act to lyse and dissolve pre-established B. subtilis biofilms.

A Comprehensive, CRISPR-based Functional Analysis of Essential Genes in Bacteria

Essential gene functions underpin the core reactions required for cell viability, but their contributions and relationships are poorly studied in vivo. Using CRISPR interference, we created knockdowns of every essential gene in Bacillus subtilis and probed their phenotypes. Our high-confidence essential gene network, established using chemical genomics, showed extensive interconnections among distantly related processes and identified modes of action for uncharacterized antibiotics. Importantly, mild knockdown of essential gene functions significantly reduced stationary-phase survival without affecting maximal growth rate, suggesting that essential protein levels are set to maximize outgrowth from stationary phase. Finally, high-throughput microscopy indicated that cell morphology is relatively insensitive to mild knockdown but profoundly affected by depletion of gene function, revealing intimate connections between cell growth and shape. Our results provide a framework for systematic investigation of essential gene functions in vivo broadly applicable to diverse microorganisms and amenable to comparative analysis.

Following the fate of bacterial cells experiencing sudden chromosome loss

Chromosomal DNA is a constant source of information, essential for any given cell to respond and adapt to changing conditions. Here, we investigated the fate of exponentially growing bacterial cells experiencing a sudden and rapid loss of their entire chromosome. Utilizing Bacillus subtilis cells harboring an inducible copy of the endogenous toxin yqcG, which encodes an endonuclease, we induced the formation of a population of cells that lost their genetic information simultaneously. Surprisingly, these DNA-less cells, termed DLCs, did not lyse immediately and exhibited normal cellular morphology for a period of at least 5 h after DNA loss. This cellular integrity was manifested by their capacity to maintain an intact membrane and membrane potential and cell wall architecture similar to those of wild-type cells. Unlike growing cells that exhibit a dynamic profile of macromolecules, DLCs displayed steady protein and RNA reservoirs. Remarkably, following DLCs by time lapse microscopy revealed that they succeeded in synthesizing proteins, elongating, and dividing, apparently forming de novo Z rings at the midcell position. Taken together, the persistence of key cellular events in DLCs indicates that the information to carry out lengthy processes is harbored within the remaining molecular components.

IMPORTANCE

Perturbing bacterial growth by the use of antibiotics targeting replication, transcription, or translation has been a subject of study for many years; however, the consequences of a more dramatic event, in which the entire bacterial chromosome is lost, have not been described. Here, we followed the fate of bacterial cells encountering an abrupt loss of their entire genome. Surprisingly, the cells preserved an intact envelope and functioning macromolecules. Furthermore, cells lacking their genome could still elongate and divide hours after the loss of DNA. Our data suggest that the information stored in the transient reservoir of macromolecules is sufficient to carry out complex and lengthy processes even in the absence of the chromosome. Based on our study, the formation of DNA-less bacteria could serve as a novel vaccination strategy, enabling an efficient induction of the immune system without the risk of bacterial propagation within the host.

Gluconate 5-dehydrogenase (Ga5DH) participates in Streptococcus suis cell division

Bacterial cell division is strictly regulated in the formation of equal daughter cells. This process is governed by a series of spatial and temporal regulators, and several new factors of interest to the field have recently been identified. Here, we report the requirement of gluconate 5-dehydrogenase (Ga5DH) in cell division of the zoonotic pathogen Streptococcus suis. Ga5DH catalyzes the reversible reduction of 5-ketogluconate to D-gluconate and was localized to the site of cell division. The deletion of Ga5DH in S. suis resulted in a plump morphology with aberrant septa joining the progeny. A significant increase was also observed in cell length. These defects were determined to be the consequence of Ga5DH deprivation in S. suis causing FtsZ delocalization. In addition, the interaction of FtsZ with Ga5DH in vitro was confirmed by protein interaction assays. These results indicate that Ga5DH may function to prevent the formation of ectopic Z rings during S. suis cell division.

Wall teichoic acids of gram-positive bacteria

The peptidoglycan layers of many gram-positive bacteria are densely functionalized with anionic glycopolymers known as wall teichoic acids (WTAs). These polymers play crucial roles in cell shape determination, regulation of cell division, and other fundamental aspects of gram-positive bacterial physiology. Additionally, WTAs are important in pathogenesis and play key roles in antibiotic resistance. We provide an overview of WTA structure and biosynthesis, review recent studies on the biological roles of these polymers, and highlight remaining questions. We also discuss prospects for exploiting WTA biosynthesis as a target for new therapies to overcome resistant infections.

Inactivation of phosphomannose isomerase gene abolishes sporulation and antibiotic production in Streptomyces coelicolor

Phosphomannose isomerases (PMIs) in bacteria and fungi catalyze the reversible conversion of D-fructose-6-phosphate to D-mannose-6-phosphate during biosynthesis of GDP-mannose, which is the main intermediate in the mannosylation of important cell wall components, glycoproteins, and certain glycolipids. In the present study, the kinetic parameters of PMI from Streptomyces coelicolor were obtained, and its function on antibiotic production and sporulation was studied. manA (SCO3025) encoding PMI in S. coelicolor was deleted by insertional inactivation. Its mutant (S. coelicolor∆manA) was found to exhibit a bld-like phenotype. Additionally, S. coelicolor∆manA failed to produce the antibiotics actinorhodin and red tripyrolle undecylprodigiosin in liquid media. To identify the function of manA, the gene was cloned and expressed in Escherichia coli BL21 (DE3). The purified recombinant ManA exhibited PMI activity (K(cat)/K(m) (mM(-1) s(-1) = 0.41 for D-mannose-6-phosphate), but failed to show GDP-D-mannose pyrophosphorylase [GMP (ManC)] activity. Complementation analysis with manA from S. coelicolor or E. coli resulted in the recovery of bld-like phenotype of S. coelicolor∆manA. SCO3026, another ORF that encodes a protein with sequence similarity towards bifunctional PMI and GMP, was also tested for its ability to function as an alternate ManA. However, the purified protein of SCO3026 failed to exhibit both PMI and GMP activity. The present study shows that enzymes involved in carbohydrate metabolism could control cellular differentiation as well as the production of secondary metabolites.

Chemical-biological studies of subcellular organization in bacteria

The subcellular organization of biological molecules is a critical determinant of many bacterial processes, including growth, replication of the genome, and division, yet the details of many mechanisms that control intracellular organization remain unknown. Decoding this information will impact the field of bacterial physiology and can provide insight into eukaryotic biology, including related processes in mitochondria and chloroplasts. Small molecule probes provide unique advantages in studying these mechanisms and manipulating the organization of biomolecules in live bacterial cells. In this review, we describe small molecules that are available for investigating subcellular organization in bacteria, specifically targeting FtsZ, MreB, peptidoglycan, and lipid bilayers. We discuss how these probes have been used to study microbiological questions and conclude by providing suggestions about important areas in which chemical-biological approaches will have a revolutionary impact on the study of bacterial physiology.

A sweet twist gets Bacillus into shape

A protective organelle that is essential for viability under most conditions, the cell wall is a dynamic structure that is continuously remodelled with the growth of the bacterial cell. Because the cell wall also moulds the bacterium, the mechanisms of cell wall homeostasis can be deciphered using cell shape as a convenient proxy. In this issue of Molecular Microbiology, Foulquier et al. illuminate a connection between cell shape regulation and metabolism in Bacillus subtilis. They find that the putative NAD(P)-binding enzyme YvcK organizes into helical subcellular structures that exert shape control by directing the cell wall biosynthetic enzyme PBP1 along the cell cylinder and to the septum, a function shared with the MreB actin cytoskeleton. Unlike MreB, however, the role of YvcK in cell shape control is manifested only on certain carbon sources, presumably by way of a previously unknown metabolic feed that taps into cell morphogenesis.