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Rotation of Vibrio fischeri Flagella Produces Outer Membrane Vesicles That Induce Host Development.

ABSTRACT:

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Using the squid-vibrio association, we aimed to characterize the mechanism through which Vibrio fischeri cells signal morphogenesis of the symbiotic light-emitting organ. The symbiont releases two cell envelope molecules, peptidoglycan (PG) and lipopolysaccharide (LPS) that, within 12 h of light organ colonization, act in synergy to trigger normal tissue development. Recent work has shown that outer membrane vesicles (OMVs) produced by V. fischeri are sufficient to induce PG-dependent morphogenesis; however, the mechanism(s) of OMV release by these bacteria has not been described. Like several genera of both beneficial and pathogenic bacteria, V. fischeri cells elaborate polar flagella that are enclosed by an extension of the outer membrane, whose function remains unclear. Here, we present evidence that along with the well-recognized phenomenon of blebbing from the cell's surface, rotation of this sheathed flagellum also results in the release of OMVs. In addition, we demonstrate that most of the development-inducing LPS is associated with these OMVs and that the presence of the outer membrane protein OmpU but not the LPS O antigen on these OMVs is important in triggering normal host development. These results also present insights into a possible new mechanism of LPS release by pathogens with sheathed flagella.

Importance

Determining the function(s) of sheathed flagella in bacteria has been challenging, because no known mutation results only in the loss of this outer membrane-derived casing. Nevertheless, the presence of a sheathed flagellum in such host-associated genera as Vibrio, Helicobacter, and Brucella has led to several proposed functions, including physical protection of the flagella and masking of their immunogenic flagellins. Using the squid-vibrio light organ symbiosis, we demonstrate another role, that of V. fischeri cells require rotating flagella to induce apoptotic cell death within surface epithelium, which is a normal step in the organ's development. Further, we present evidence that this rotation releases apoptosis-triggering lipopolysaccharide in the form of outer membrane vesicles. Such release may also occur by pathogens but with different outcomes for the host.

SUBMITTER: Aschtgen MS

PROVIDER: S-EPMC4966437 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Rotation of Vibrio fischeri Flagella Produces Outer Membrane Vesicles That Induce Host Development.

Aschtgen Marie-Stephanie MS Lynch Jonathan B JB Koch Eric E Schwartzman Julia J McFall-Ngai Margaret M Ruby Edward E

Journal of bacteriology 20160728 16

<h4>Unlabelled</h4>Using the squid-vibrio association, we aimed to characterize the mechanism through which Vibrio fischeri cells signal morphogenesis of the symbiotic light-emitting organ. The symbiont releases two cell envelope molecules, peptidoglycan (PG) and lipopolysaccharide (LPS) that, within 12 h of light organ colonization, act in synergy to trigger normal tissue development. Recent work has shown that outer membrane vesicles (OMVs) produced by V. fischeri are sufficient to induce PG-d ...[more]

PMID: 27246572

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Project description:The nascent light-emitting organ of newly hatched juveniles of the Hawaiian sepiolid squid Euprymna scolopes is specifically colonized by cells of Vibrio fischeri that are obtained from the ambient seawater. The mechanisms that promote this specific, cooperative colonization are likely to require a number of bacterial and host-derived factors and activities, only some of which have been described to date. A characteristic of many host-pathogen associations is the presence of bacterial mechanisms that allow attachment to specific tissues. These mechanisms have been well characterized and often involve bacterial fimbriae or outer membrane proteins (OMPs) that act as adhesins, the expression of which has been linked to virulence regulators such as ToxR in Vibrio cholerae. Analogous or even homologous mechanisms are probably operative in the initiation and persistence of cooperative bacterial associations, although considerably less is known about them. We report the presence in V. fischeri of ompU, a gene encoding a 32.5-kDa protein homolog of two other OMPs, OmpU of V. cholerae (50.8% amino acid sequence identity) and OmpL of Photobacterium profundum (45.5% identity). A null mutation introduced into the V. fischeri ompU resulted in the loss of an OMP with an estimated molecular mass of about 34 kDa; genetic complementation of the mutant strain with a DNA fragment containing only the ompU gene restored the production of this protein. The expression of the V. fischeri OmpU was not significantly affected by either (i) iron or phosphate limitation or (ii) a mutation that renders V. fischeri defective in the synthesis of a homolog of the OMP-regulatory protein ToxR. The ompU mutant grew normally in complex nutrient media but was more susceptible to growth inhibition in the presence of either anionic detergents or the antimicrobial peptide protamine sulfate. Interestingly, colonization experiments showed that the ompU null mutant initiated a symbiotic association with juvenile light organ tissue with only about 60% of the effectiveness of the parent strain. When colonization did occur, it proceeded more slowly and resulted in an approximately fourfold-smaller bacterial population. Surprisingly, there was no evidence that in a mixed infection with its parent, the ompU-defective strain had a competitive disadvantage, suggesting that the presence of the parent strain provided a shared compensatory activity. Thus, the OmpU protein appears to play a role in the normal process by which V. fischeri initiates its colonization of the nascent light organ of juvenile squids.

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Dataset Information

Rotation of Vibrio fischeri Flagella Produces Outer Membrane Vesicles That Induce Host Development.

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Importance

Publications

Rotation of Vibrio fischeri Flagella Produces Outer Membrane Vesicles That Induce Host Development.

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