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Environmental Sensing and Cell-Cell Communication

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Environmental Sensing and Cell-Cell Communication
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The last two decades have provided a wealth of new insight into how microbes (both prokaryotes and eukaryotes) sense and respond to their surroundings and to one another. Technological advances continue to shape our understanding of this burgeoning field, and this has led to a sea-change in the way in which we view the microbial world. No longer are microbes viewed as being the archetypal single celled entities; instead, community spirit and coordinated responses are the order of the day. In this special anniversary collection for Microbiology, timed to coincide with the Microbiology Society-sponsored Cell-Cell Communication meeting, Guest Editors Martin Welch (University of Cambridge) and Anugraha Mathew (University of Zurich) aim to assemble a landmark collection of papers that celebrate the interaction of microbes with their environment and with one another.

Submissions are particularly welcomed on microbial sensing and signaling pathways, quorum sensing (including both intra- and inter-species interactions and other forms of community-wide behaviors), chemoreception, secondary metabolism, and the complex interplay between different sensory pathways.

Collection Contents

6 results

    • Exposure to the secretome alters the proteome and secondary metabolite production of

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      The fungal pathogen is frequently cultured from the sputum of cystic fibrosis (CF) patients along with the bacterium secretes a range of secondary metabolites, and one of these, gliotoxin, has inhibitory effects on the host immune response. The effect of culture filtrate (CuF) on fungal growth and gliotoxin production was investigated. Exposure of hyphae to cells induced increased production of gliotoxin and a decrease in fungal growth. In contrast, exposure of hyphae to CuF led to increased growth and decreased gliotoxin production. Quantitative proteomic analysis was used to characterize the proteomic response of upon exposure to CuF. Changes in the profile of proteins involved in secondary metabolite biosynthesis (e.g. gliotoxin, fumagillin, pseurotin A), and changes to the abundance of proteins involved in oxidative stress (e.g. formate dehydrogenase) and detoxification (e.g. thioredoxin reductase) were observed, indicating that the bacterial secretome had a profound effect on the fungal proteome. Alterations in the abundance of proteins involved in detoxification and oxidative stress highlight the ability of to differentially regulate protein synthesis in response to environmental stresses imposed by competitors such as . Such responses may ultimately have serious detrimental effects on the host.

    • How bacteria utilize sialic acid during interactions with the host: snip, snatch, dispatch, match and attach

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      -glycolylneuraminic acid (Neu5Gc), and its precursor -acetylneuraminic acid (Neu5Ac), commonly referred to as sialic acids, are two of the most common glycans found in mammals. Humans carry a mutation in the enzyme that converts Neu5Ac into Neu5Gc, and as such, expression of Neu5Ac can be thought of as a ‘human specific’ trait. Bacteria can utilize sialic acids as a carbon and energy source and have evolved multiple ways to take up sialic acids. In order to generate free sialic acid, many bacteria produce sialidases that cleave sialic acid residues from complex glycan structures. In addition, sialidases allow escape from innate immune mechanisms, and can synergize with other virulence factors such as toxins. Human-adapted pathogens have evolved a preference for Neu5Ac, with many bacterial adhesins, and major classes of toxin, specifically recognizing Neu5Ac containing glycans as receptors. The preference of human-adapted pathogens for Neu5Ac also occurs during biosynthesis of surface structures such as lipo-oligosaccharide (LOS), lipo-polysaccharide (LPS) and polysaccharide capsules, subverting the human host immune system by mimicking the host. This review aims to provide an update on the advances made in understanding the role of sialic acid in bacteria-host interactions made in the last 5–10 years, and put these findings into context by highlighting key historical discoveries. We provide a particular focus on ‘molecular mimicry’ and incorporation of sialic acid onto the bacterial outer-surface, and the role of sialic acid as a receptor for bacterial adhesins and toxins.

    • -Serine induces distinct transcriptomes in diverse pathotypes

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      Appropriate interpretation of environmental signals facilitates niche specificity in pathogenic bacteria. However, the responses of niche-specific pathogens to common host signals are poorly understood. -Serine (-ser) is a toxic metabolite present in highly variable concentrations at different colonization sites within the human host that we previously found is capable of inducing changes in gene expression. In this study, we made the striking observation that the global transcriptional response of three pathotypes – enterohaemorrhagic (EHEC), uropathogenic (UPEC) and neonatal meningitis-associated (NMEC) – to -ser was highly distinct. In fact, we identified no single differentially expressed gene common to all three strains. We observed the induction of ribosome-associated genes in extraintestinal pathogens UPEC and NMEC only, and the induction of purine metabolism genes in gut-restricted EHEC, and UPEC indicating distinct transcriptional responses to a common signal. UPEC and NMEC encode – a genetic locus required for detoxification and hence normal growth in the presence of -ser. Specific transcriptional responses were induced in strains accumulating -ser (WT EHEC and UPEC/NMEC mutants lacking the -ser-responsive transcriptional activator DsdC), corroborating the notion that -ser is an unfavourable metabolite if not metabolized. Importantly, many of the UPEC-associated transcriptome alterations correlate with published data on the urinary transcriptome, supporting the hypothesis that -ser sensing forms a key part of urinary niche adaptation in this pathotype. Collectively, our results demonstrate distinct pleiotropic responses to a common metabolite in diverse pathotypes, with important implications for niche selectivity.

    • Biofilm hydrophobicity in environmental isolates of

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      Biofilms are communities of bacteria that are attached to a surface and surrounded by an extracellular matrix. The extracellular matrix protects the community from stressors in the environment, making biofilms robust. The Gram-positive soil bacterium particularly the isolate NCIB 3610, is widely used as a model for studying biofilm formation. NCIB 3610 forms colony biofilms that are architecturally complex and highly hydrophobic. The hydrophobicity is linked, in part, to the localisation of the protein BslA at the surface of the biofilm, which provides the community with increased resistance to biocides. As most of our knowledge about biofilm formation comes from one isolate, it is unclear if biofilm hydrophobicity is a widely distributed feature of the species. To address this knowledge gap, we collated a library of soil isolates and acquired their whole genome sequences. We used our novel isolates to examine biofilm hydrophobicity and found that, although BslA is encoded and produced by all isolates in our collection, hydrophobicity is not a universal feature of colony biofilms. To test whether the matrix exopolymer poly γ-glutamic acid could be masking hydrophobicity in our hydrophilic isolates, we constructed deletion mutants and found, contrary to our hypothesis, that the presence of poly γ-glutamic acid was not the reason for the observed hydrophilicity. This study highlights the natural variation in the properties of biofilms formed by different isolates and the importance of using a more diverse range of isolates as representatives of a species.

    • The role of -arabinose metabolism for O157:H7 in edible plants

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      Arabinose is a major plant aldopentose in the form of arabinans complexed in cell wall polysaccharides or glycoproteins (AGP), but comparatively rare as a monosaccharide. -arabinose is an important bacterial metabolite, accessed by pectolytic micro-organisms such as via pectin and hemicellulose degrading enzymes. However, not all plant-associated microbes encode cell-wall-degrading enzymes, yet can metabolize -arabinose, raising questions about their use of and access to the glycan in plants. Therefore, we examined -arabinose metabolism in the food-borne pathogen O157:H7 (isolate Sakai) during its colonization of plants. -arabinose metabolism () and transport () genes were activated at 18 °C by -arabinose and expressed over prolonged periods . Although deletion of did not impact the colonization ability of O157:H7 (Sakai) on spinach and lettuce plants (both associated with STEC outbreaks), was induced on exposure to spinach cell-wall polysaccharides. Furthermore, debranched and arabinan oligosaccharides induced metabolism gene expression , and stimulated modest proliferation, while immobilized pectin did not. Thus, O157:H7 (Sakai) can utilize pectin/AGP-derived -arabinose as a metabolite. Furthermore, it differs fundamentally in gene organization, transport and regulation from the related pectinolytic species , reflective of distinct plant-associated lifestyles.

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