Search

The Porphyromonas gingivalis type IX secretion system (T9SS) promotes periodontal disease by secreting gingipains and other virulence factors. By in situ cryoelectron tomography, we report that the P. gingivalis T9SS consists of 18 PorM dimers arranged as a large, caged ring in the periplasm. Near the outer membrane, PorM dimers interact with a PorKN ring complex of ∼52 nm in diameter. PorMKN translocation complexes of a given T9SS adopt distinct conformations energized by the proton motive force, suggestive of different activation states. At the inner membrane, PorM associates with a cytoplasmic complex that exhibits 12-fold symmetry and requires both PorM and PorL for assembly. Activated motors deliver substrates across the outer membrane via one of eight Sov translocons arranged in a ring. The T9SSs are unique among known secretion systems in bacteria and eukaryotes in their assembly as supramolecular machines composed of apparently independently functioning translocation motors and export pores. [ABSTRACT FROM AUTHOR]

The transcriptional regulator CcpN of Bacillus subtilis has been recently characterized as a repressor of two gluconeogenic genes, gapB and pckA, and of a small noncoding regulatory RNA, srl, involved in arginine catabolism. Deletion of ccpN impairs growth on glucose and strongly alters the distribution of intracellular fluxes, rerouting the main glucose catabolism from glycolysis to the pentose phosphate (PP) pathway. Using transcriptome analysis, we show that during growth on glucose, gapB and pckA are the only protein-coding genes directly repressed by CcpN. By quantifying intracellular fluxes in deletion mutants, we demonstrate that derepression of pckA under glycolytic condition causes the growth defect observed in the ccpN mutant due to extensive futile cycling through the pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and pyruvate kinase. Beyond ATP dissipation via this cycle, PckA activity causes a drain on tricarboxylic acid cycle intermediates, which we show to be the main reason for the reduced growth of a ccpN mutant. The high flux through the PP pathway in the ccpN mutant is modulated by the flux through the alternative glyceraldehyde-3-phosphate dehydrogenases, GapA and GapB. Strongly increased concentrations of intermediates in upper glycolysis indicate that GapB overexpression causes a metabolic jamming of this pathway and, consequently, increases the relative flux through the PP pathway. In contrast, derepression of srl, the third known target of CcpN, plays only a marginal role in ccpN mutant phenotypes.

The structural and thermodynamic consequences of fructose-1,6-biphosphate (FBP) binding to CggR is demonstrated. The CggR is the transcriptional repressor of the gapA operon encoding central glycolytic enzymes in Bacillus subtilis.

The Bacillus subtilis genome contains several sets of paralogs. An extreme case is the four putative malic enzyme genes maeA, malS, ytsJ, and mleA. maeA was demonstrated to encode malic enzyme activity, to be inducible by malate, but also to be dispensable for growth on malate. We report systematic experiments to test whether these four genes ensure backup or cover different functions. Analysis of single- and multiple-mutant strains demonstrated that ytsJ has a major physiological role in malate utilization for which none of the other three genes could compensate. In contrast, maeA, malS, and mleA had distinct roles in malate utilization for which they could compensate one another. The four proteins exhibited malic enzyme activity; MalS, MleA, and MaeA exhibited 4- to 90-fold higher activities with NA[D.sup.+] than with NAD[P.sup.+]. YtsJ activity, in contrast, was 70-fold higher with NAD[P.sup.+] than with NA[D.sup.+], with [K.sub.m] values of 0.055 and 2.8 mM, respectively, lacZ fusions revealed strong transcription of ytsJ, twofold higher in malate than in glucose medium, but weak transcription of malS and mleA. In contrast, mleA was strongly transcribed in complex medium. Metabolic flux analysis confirmed the major role of YtsJ in malate-to-pyruvate interconversion. While overexpression of the NADP-dependent Escherichia coli malic enzyme MaeB did not suppress the growth defect of a ytsJ mutant on malate, overexpression of the transhydrogenase UdhA from E. coli partially suppressed it. These results suggest an additional physiological role of YtsJ beyond that of malate-to-pyruvate conversion.

A transcriptome comparison of a wild-type Bacillus subtilis strain growing under glycolytic or gluconeogenic conditions was performed. In particular, it revealed that the ywkA gene, one of the four paralogues putatively encoding a malic enzyme, was more transcribed during gluconeogenesis. Using a lacZ reporter fusion to the ywkA promoter, it was shown that ywkA was specifically induced by external malate and not subject to glucose catabolite repression. Northern analysis confirmed this expression pattern and demonstrated that ywkA is cotranscribed with the downstream ywkB gene. The ywkA gene product was purified and biochemical studies demonstrated its malic enzyme activity, which was 10-fold higher with NAD than with NADP ([k.sub.cat]/[K.sub.m] 102 and 10 [s.sup.-1] m[M.sup.-1], respectively). However, physiological tests with single and multiple mutant strains affected in ywkA and/or in ywkA paralogues showed that ywkA does not contribute to efficient utilization of malate for growth. Transposon mutagenesis allowed the identification of the uncharacterized YufL/YufM two-component system as being responsible for the control of ywkA expression. Genetic analysis and in vitro studies with purified YufM protein showed that YufM binds just upstream of ywkA promoter and activates ywkA transcription in response to the presence of malate in the extracellular medium, transmitted by YufL. ywkA and yufL/yufM could thus be renamed maeA for malic enzyme and malK/malR for malate kinase sensor/malate response regulator, respectively.

Bacterial competition may rely on secretion systems such as the type 6 secretion system (T6SS), which punctures and releases toxic molecules into neighboring cells. To subsist, bacterial targets must counteract the threats posed by T6SS-positive competitors. In this study, we used a comprehensive genome-wide high-throughput screening approach to investigate the dynamics of interbacterial competition. Our primary goal was to identify deletion mutants within the well-characterized E. coli K-12 single-gene deletion library, the Keio collection, that demonstrated resistance to T6SS-mediated killing by the enteropathogenic bacterium Cronobacter malonaticus . We identified 49 potential mutants conferring resistance to T6SS and focused our interest on a deletion mutant (∆ fimE ) exhibiting enhanced expression of type 1 fimbriae. We demonstrated that the presence of type 1 fimbriae leads to the formation of microcolonies and thus protects against T6SS-mediated assaults. Collectively, our study demonstrated that adhesive structures such as type 1 fimbriae confer collective protective behavior against T6SS attacks.IMPORTANCEType 6 secretion systems (T6SS) are molecular weapons employed by gram-negative bacteria to eliminate neighboring microbes. T6SS plays a pivotal role as a virulence factor, enabling pathogenic gram-negative bacteria to compete with the established communities to colonize hosts and induce infections. Gaining a deeper understanding of bacterial interactions will allow the development of strategies to control the action of systems such as the T6SS that can manipulate bacterial communities. In this context, we demonstrate that bacteria targeted by T6SS attacks from the enteric pathogen Cronobacter malonaticus , which poses a significant threat to infants, can develop a collective protective mechanism centered on the production of type I fimbriae. These adhesive structures promote the aggregation of bacterial preys and the formation of microcolonies, which protect the cells from T6SS attacks., Competing Interests: The authors declare no conflict of interest.

Proteases are enzymes that catalyze the hydrolytic degradation of other proteins into peptides or amino acids through the digestion of the peptide bond. Promiscuous proteases that target a wide range of proteins are distinguished from specific proteases that have a narrow range of substrates. In terms of activity, endoproteases cleave their substrates at specific residues within the target proteins, whereas exoproteases cleave from one extremity and may have processive activities. Proteases are therefore very useful tools to study proteins, notably their structure or conformation. In addition, proteases can be used to probe the topology of bacterial membrane proteins. Here, we describe limited protease accessibility assays to define inner membrane protein topology and conformational changes based on digestion profiles., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

The type VI secretion system (T6SS) is a contractile nanomachine widespread in Gram-negative bacteria. The T6SS injects effectors into target cells including eukaryotic hosts and competitor microbial cells and thus participates in pathogenesis and intermicrobial competition. Pseudomonas fluorescens MFE01 possesses a single T6SS gene cluster that confers biocontrol properties by protecting potato tubers against the phytopathogen Pectobacterium atrosepticum (Pca). Here, we demonstrate that a functional T6SS is essential to protect potato tuber by reducing the pectobacteria population. Fluorescence microscopy experiments showed that MFE01 displays an aggressive behaviour with an offensive T6SS characterized by continuous and intense T6SS firing activity. Interestingly, we observed that T6SS firing is correlated with rounding of Pectobacterium cells, suggesting delivery of a potent cell wall targeting effector. Mutagenesis coupled with functional assays then revealed that a putative T6SS secreted amidase, Tae3 Pf , is mainly responsible for MFE01 toxicity towards Pca. Further studies finally demonstrated that Tae3 Pf is toxic when produced in the periplasm, and that its toxicity is counteracted by the Tai3 Pf inner membrane immunity protein., (© 2023 The Authors. Environmental Microbiology published by Applied Microbiology International and John Wiley & Sons Ltd.)

Bacteria are able to adapt to nutrient availability in the environment. For example, when nutritional conditions are not favorable, bacterial size can be reduced and duplication time can be significantly extended in comparison to rich growth conditions. These observations suggest that essential cellular processes like cell division, morphogenesis and chromosome dynamics are highly coordinated with central metabolism to ensure the production of fit progeny. The aim of this review is to provide an overview extending from physiological observations done more than fifty years ago to recent discoveries showing strategies to control essential functions in relation with metabolism in the model bacterium Bacillus subtilis.