Author
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Welch, Timothy - Tim |
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CROSA, JORGE - OREGON HEALTH AND SCIENCE |
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Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/22/2005 Publication Date: 8/1/2005 Citation: Welch, T.J., Crosa, J. 2005. Novel role of the lipopolysaccharide o1-side chain in ferric-siderophore transport and virulence of vibrio anguillarum. Infection and Immunity Vol. 73 No 9, 5864-5872. Interpretive Summary: Infectious diseases are a major impediment to efficient aquatic animal production and cause losses estimated at $ 1 billion annually. To develop improved strategies for disease control a better understanding of the host-pathogen interactions leading to the diseases state are needed. In this manuscript we document the discovery of the dual role that a surface polysaccharide plays in the virulence of the fish pathogen Vibrio anguillarum. Strains which were engineered to not produce this surface exposed polysaccharide showed reduced levels of iron scavenging activity and a loss of resistance to the bactericidal action of fish serum, both of these bacterial factors are needed by the bacterium in order for it to cause disease. This novel finding broadens our general understanding of the factors needed by bacterial pathogens of fish and may be useful in the design of safe vaccines. Technical Abstract: From a library of approximately 20,000 transposition-generated mutants we have identified mutants affected in chromosomal genes involved in synthesis of the siderophore anguibactin as well as in ferric-anguibactin utilization. Genetic and sequence analysis of one such transport-defective mutant revealed that the transposon insertion occurred in rmlC, a dTDP-rhamnose biosynthetic gene residing within a cluster of four genes all of which are predicted to function in the biosynthesis of this O side chain precursor. The same phenotype was seen in a mutant obtained by allelic exchange in rmlD, the furthest downstream gene in this dTDP-rhamnose biosynthetic gene cluster. This mutation could be complemented with the wild type rmlD gene restoring both production of the O1 antigen side chain and ferric anguibactin transport. Presence of the O1 side chain was crucial for the resistance of V. anguillarum to the bactericidal action of non-immune serum from the fish host. Surprisingly, further analyses demonstrated that these mutations were pleiotropic, leading to a reduction in the wild type levels of FatA, the outer membrane protein receptor for ferric anguibactin transport and thus cause a concomitant reduction in iron transport. Thus, our results in this work demonstrate that the LPS O1 side chain is required for the operation of two critical virulence factors in V. anguillarum: serum resistance and anguibactin mediated iron transport. These factors allow V. anguillarum to survive in serum and multiplying in the iron-limiting milieu of the host vertebrate. |
