Burkholderia Type VI Secretion Systems Have Distinct Roles in Eukaryotic and Bacterial Cell Interactions

Department of Microbiology, University of Washington, Seattle, Washington, United States of America.
PLoS Pathogens (Impact Factor: 7.56). 08/2010; 6(8):e1001068. DOI: 10.1371/journal.ppat.1001068
Source: PubMed


Bacteria that live in the environment have evolved pathways specialized to defend against eukaryotic organisms or other bacteria. In this manuscript, we systematically examined the role of the five type VI secretion systems (T6SSs) of Burkholderia thailandensis (B. thai) in eukaryotic and bacterial cell interactions. Consistent with phylogenetic analyses comparing the distribution of the B. thai T6SSs with well-characterized bacterial and eukaryotic cell-targeting T6SSs, we found that T6SS-5 plays a critical role in the virulence of the organism in a murine melioidosis model, while a strain lacking the other four T6SSs remained as virulent as the wild-type. The function of T6SS-5 appeared to be specialized to the host and not related to an in vivo growth defect, as ΔT6SS-5 was fully virulent in mice lacking MyD88. Next we probed the role of the five systems in interbacterial interactions. From a group of 31 diverse bacteria, we identified several organisms that competed less effectively against wild-type B. thai than a strain lacking T6SS-1 function. Inactivation of T6SS-1 renders B. thai greatly more susceptible to cell contact-induced stasis by Pseudomonas putida, Pseudomonas fluorescens and Serratia proteamaculans-leaving it 100- to 1000-fold less fit than the wild-type in competition experiments with these organisms. Flow cell biofilm assays showed that T6S-dependent interbacterial interactions are likely relevant in the environment. B. thai cells lacking T6SS-1 were rapidly displaced in mixed biofilms with P. putida, whereas wild-type cells persisted and overran the competitor. Our data show that T6SSs within a single organism can have distinct functions in eukaryotic versus bacterial cell interactions. These systems are likely to be a decisive factor in the survival of bacterial cells of one species in intimate association with those of another, such as in polymicrobial communities present both in the environment and in many infections.

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Available from: Laurence Rohmer, Oct 08, 2015
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    • "Whereas RovM represses the expression of AR3 acidic stress under nutrient-limiting conditions, it simultaneously activates the expression of T6SS4, a novel acid tolerance system recently identified in Y. pseudotuberculosis (Zhang et al., 2013). Besides their involvement in host–symbiont communication, interbacterial competition and biofilm formation, some T6SSs have been shown to play roles in stress response and survival after exposure to various environmental challenges (Filloux et al., 2008; Weber et al., 2009; Hood et al., 2010; Schwarz et al., 2010; Wu et al., 2012; RovM conversely regulates AR3 and T6SS4 9 Gueguen et al., 2013; Ho et al., 2014). The Yersinia T6SS4 is essential for bacterial survival under mildly acidic conditions by pumping H + out of the cell to maintain intracellular pH homeostasis. "
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    ABSTRACT: Coordinated regulation of various acid survival systems in response to environmental stimuli is crucial for the adaptation of enteropathogenic bacteria to acidic environments such as the stomach. In this study, we demonstrated that the RovM protein, a central regulator of the CsrABC-RovM-RovA cascade, conversely regulates the expression of two acid survival systems in Yersinia pseudotuberculosis by acting as a dual transcriptional regulator. RovM activated the expression of T6SS4, which is essential for bacterial survival under mild acidic conditions, by binding upstream of the T6SS4 promoter. On the contrary, RovM repressed the expression of a functional arginine-dependent acid resistance system (AR3), which is crucial for bacterial survival under strong acidic conditions, by directly binding to the -35 element in the AR3 promoter. Consistent with previous findings that rovM expression responds to the availability of nutrients, the expression of T6SS4 and AR3 were differentially regulated by nutritional status. Based on these results, a dynamic model whereby RovM coordinately regulates the expression of AR3 and T6SS4 in response to the availability of nutrients in the environment was proposed. This article is protected by copyright. All rights reserved.
    Environmental Microbiology 07/2015; DOI:10.1111/1462-2920.12996 · 6.20 Impact Factor
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    • "Functional assays and protein localization studies suggest that these proteins assemble into a multi-component secretory apparatus similar to a bacteriophage-like structure, injecting effector proteins into eukaryotic target host cells [11,15,16]. In addition, the T6SS also contains antibacterial properties against competitor bacterial cells upon cell-to-cell contact [17] [18]. In B. pseudomallei, six clusters of T6SS (T6SS-1, -2, -3, -4, -5 and -6) have been described [10] although experimental evidence is only available for T6SS-5. "
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    ABSTRACT: Burkholderia pseudomallei, the causative agent of melioidosis, is able to survive extreme environments and utilizes various virulence factors for survival and pathogenicity. To compete and survive within these different ecological niches, B. pseudomallei has evolved specialized pathways, including the Type VI secretion systems (T6SSs), that have a role in pathogenesis as well as interbacterial interactions. We examined the expression profile of B. pseudomallei T6SS six gene clusters during infection of U937 macrophage cells. T6SS-5 was robustly transcribed while the other five clusters were not significantly regulated proposing the utility of T6SS-5 as a potential biomarker of exposure to B. pseudomallei. Transcription of T6SS regulators VirAG and BprB was also not significant during infection when compared to bacteria grown in culture. Guided by these findings, three highly expressed T6SS genes, tssJ-4, hcp1 and tssE-5, were expressed as recombinant proteins and screened against melioidosis patient sera by western analysis and ELISA. Only Hcp1 was reactive by both types of analysis. The recombinant Hcp1 protein was further evaluated against a cohort of melioidosis patients (n=32) and non-melioidosis individuals (n=20) sera and the data clearly indicates a higher sensitivity (93.7%) and specificity (100%) for Hcp1 compared to bacterial lysate. The detection of anti-Hcp1 antibodies in patients' sera indicating the presence of B. pseudomallei highlights the potential of Hcp1 to be further developed as a serodiagnostic marker for melioidosis. Copyright © 2015. Published by Elsevier Ltd.
    Microbial Pathogenesis 01/2015; 79. DOI:10.1016/j.micpath.2015.01.006 · 1.79 Impact Factor
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    • "By analogy with T6SS i and T6SS ii , it is reasonable to speculate that T6SS iii has the capacity to mediate host cell interactions in addition to its now established role in interbacterial antagonism. Certain T6SS i and T6SS ii pathways appear to specialize in either bacterial or host cell targeting, whereas others can act on both cell types (Hood et al., 2010; MacIntyre et al., 2010; Pukatzki et al., 2007; Schwarz et al., 2010b). Target range appears to be dictated, at least in part, by the specific complement and corresponding activities of the effectors transported by a system. "
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    ABSTRACT: Bacteroidetes are a phylum of Gram-negative bacteria abundant in mammalian-associated polymicrobial communities, where they impact digestion, immunity, and resistance to infection. Despite the extensive competition at high cell density that occurs in these settings, cell contact-dependent mechanisms of interbacterial antagonism, such as the type VI secretion system (T6SS), have not been defined in this group of organisms. Herein we report the bioinformatic and functional characterization of a T6SS-like pathway in diverse Bacteroidetes. Using prominent human gut commensal and soil-associated species, we demonstrate that these systems localize dynamically within the cell, export antibacterial proteins, and target competitor bacteria. The Bacteroidetes system is a distinct pathway with marked differences in gene content and high evolutionary divergence from the canonical T6S pathway. Our findings offer a potential molecular explanation for the abundance of Bacteroidetes in polymicrobial environments, the observed stability of Bacteroidetes in healthy humans, and the barrier presented by the microbiota against pathogens.
    Cell host & microbe 08/2014; 16(2). DOI:10.1016/j.chom.2014.07.007 · 12.33 Impact Factor
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