Mucosal penetration primes Vibrio cholerae for host colonization by repressing quorum sensing

Departments of Microbiology, Physics, and Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2008; 105(28):9769-74. DOI: 10.1073/pnas.0802241105
Source: PubMed


To successfully infect a host and cause the diarrheal disease cholera, Vibrio cholerae must penetrate the intestinal mucosal layer and express virulence genes. Previous studies have demonstrated that the transcriptional regulator HapR, which is part of the quorum sensing network in V. cholerae, represses the expression of virulence genes. Here, we show that hapR expression is also modulated by the regulatory network that governs flagellar assembly. Specifically, FliA, which is the alternative sigma-factor (sigma(28)) that activates late-class flagellin genes in V. cholerae, represses hapR expression. In addition, we show that mucin penetration by V. cholerae is sufficient to break flagella and so cause the secretion of FlgM, the anti-sigma factor that inhibits FliA activity. During initial colonization of host intestinal tissue, hapR expression is repressed because of low cell density. However, full repression of hapR expression does not occur in fliA mutants, which results in attenuated colonization. Our results suggest that V. cholerae uses flagellar machinery to sense particular intestinal signals before colonization and enhance the expression of virulence genes by modulating the output of quorum sensing signaling.

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Available from: Zhi Liu, Aug 25, 2014
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    • "HapR is a transcriptional regulator involved in quorum sensing in V. cholerae which also regulates expression of virulence genes. HapR represses expression of several virulence genes [101] and hapR expression is regulated by an unknown mechanism involving FliA [102]. hapR expression is depressed in flgM and flgD mutants (both of these mutations alleviate FlgM repression on FliA activity), while deletion of fliA results in elevated hapR expression [102]. "
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    ABSTRACT: Flagellar biogenesis in bacteria is a complex process in which the transcription of dozens of structural and regulatory genes is coordinated with the assembly of the flagellum. Although the overall process of flagellar biogenesis is conserved among bacteria, the mechanisms used to regulate flagellar gene expression vary greatly among different bacterial species. Many bacteria use the alternative sigma factor σ (54) (also known as RpoN) to transcribe specific sets of flagellar genes. These bacteria include members of the Epsilonproteobacteria (e.g., Helicobacter pylori and Campylobacter jejuni), Gammaproteobacteria (e.g., Vibrio and Pseudomonas species), and Alphaproteobacteria (e.g., Caulobacter crescentus). This review characterizes the flagellar transcriptional hierarchies in these bacteria and examines what is known about how flagellar gene regulation is linked with other processes including growth phase, quorum sensing, and host colonization.
    01/2014; 2014(12):681754. DOI:10.1155/2014/681754
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    • "Flagellar motility is an environmentally regulated behavior by which a bacterium propels itself through its surroundings , directed by behavior-modifying machinery such as the chemotaxis system (Adler 1966; Henrichsen 1972; reviewed in Macnab 1996; and McCarter 2006). Within the unique environments present in different host– microbe associations, both flagellar motility and the flagellum itself can play important roles in bacterial transit , niche specificity, effector secretion, biofilm formation, host recognition, and gene regulation (Young et al. 1999; Hayashi et al. 2001; Butler and Camilli 2004; Lemon et al. 2007; Liu et al. 2008). While the process of flagellar motility is difficult to study in most host–microbe interactions, the symbiosis between the bioluminescent, gram-negative bacterium Vibrio fischeri and its host the Hawaiian bobtail squid, Euprymna scolopes, is an ideal model in which to study how this critical behavior mediates symbiotic initiation. "
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    ABSTRACT: Bacterial flagellar motility is a complex cellular behavior required for the colonization of the light-emitting organ of the Hawaiian bobtail squid, Euprymna scolopes, by the beneficial bioluminescent symbiont Vibrio fischeri. We characterized the basis of this behavior by performing (i) a forward genetic screen to identify mutants defective in soft-agar motility, as well as (ii) a transcriptional analysis to determine the genes that are expressed downstream of the flagellar master regulator FlrA. Mutants with severe defects in soft-agar motility were identified due to insertions in genes with putative roles in flagellar motility and in genes that were unexpected, including those predicted to encode hypothetical proteins and cell division-related proteins. Analysis of mutants for their ability to enter into a productive symbiosis indicated that flagellar motility mutants are deficient, while chemotaxis mutants are able to colonize a subset of juvenile squid to light-producing levels. Thirty-three genes required for normal motility in soft agar were also downregulated in the absence of FlrA, suggesting they belong to the flagellar regulon of V. fischeri. Mutagenesis of putative paralogs of the flagellar motility genes motA, motB, and fliL revealed that motA1, motB1, and both fliL1 and fliL2, but not motA2 and motB2, likely contribute to soft-agar motility. Using these complementary approaches, we have characterized the genetic basis of flagellar motility in V. fischeri and furthered our understanding of the roles of flagellar motility and chemotaxis in colonization of the juvenile squid, including identifying 11 novel mutants unable to enter into a productive light-organ symbiosis.
    MicrobiologyOpen 08/2013; 2(4). DOI:10.1002/mbo3.96 · 2.21 Impact Factor
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    • "We then expressed KatG-FLAG and KatB-FLAG in V. cholerae and used a western blot analysis to determine the localization of catalases. We found that both KatG and KatB were presented in culture supernatants (Fig. 5A–B), however, cytoplasmic protein HapR [20], [26] was also detected in the supernatants from the same samples (Fig. 5C–D), implying that the presence of catalases in the supernatant resulted from cell lysis. "
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    ABSTRACT: Oxidative stress is a major challenge faced by bacteria. Many bacteria control oxidative stress resistance pathways through the transcriptional regulator OxyR. The human pathogen Vibrio cholerae is a Gram-negative bacterium that is the causative agent of cholera. V. cholerae lives in both aquatic environments and human small intestines, two environments in which it encounters reactive oxygen species (ROS). To study how V. cholerae responds to oxidative stress, we constructed an in-frame oxyR deletion mutant. We found that this mutant was not only sensitive to H(2)O(2), but also displayed a growth defect when diluted in rich medium. Further study showed that two catalases, KatG and KatB, either when expressed in living cells, present in culture supernatants, or added as purified recombinant proteins, could rescue the oxyR growth defect. Furthermore, although it could colonize infant mouse intestines similar to that of wildtype, the oxyR mutant was defective in zebrafish intestinal colonization. Alternatively, co-infection with wildtype, but not katG-katB deletion mutants, greatly enhanced oxyR mutant colonization. Our study suggests that OxyR in V. cholerae is critical for antioxidant defense and that the organism is capable of scavenging environmental ROS to facilitate population growth.
    PLoS ONE 12/2012; 7(12):e53383. DOI:10.1371/journal.pone.0053383 · 3.23 Impact Factor
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