Evolution of the leukotoxin operon in genus Mannheimia

J. Larsen, A. G. Pedersen, H. Christensen, M. Bisgaard, Øystein Angen, Peter Ahrens, J. E. Olsen

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    The leukotoxin protein of Mannheimia haemolytica belongs to the HlyA-like subfamily of cytotoxic RTX (repeats in toxin) proteins. To test the hypothesis that different lineages of genus Mannheimia gained the leukotoxin operon via horizontal gene transfer we used a strategy that combines compositional and phylogenetic methods: (i) ranking of genes according to their convergence to the average genome signature of M. haemolytica based on the relative 3:1 dinucleotide bias in 56 individual genes; (ii) estimation of ancestral character states on a phylogeny of 43 Mannheimia strains based on 16S rRNA sequences; (iii) phylogeny of 24 leukotoxin gene sequences and 16 homologous genes retrieved from SWISS-PROT by using PSI-BLAST. Our data show no evidence for horizontal gene transfer into this clade. We propose that vertical descent from the common ancestor of genus Mannheimia, with subsequent loss of these genes in many strains can explain the patchy distribution of leukotoxin in this clade. Finally, we argue that antagonistic pleiotropy was the main contributor to gene loss in the radiating M. ruminalis lines, which have adapted to different ecological niches in the rumen offering different conditions of growth.
    Original languageEnglish
    Title of host publicationPasteurellaceae 2005
    Number of pages99
    PublisherASM International
    Publication date2005
    ISBN (Print)1-55581-370-4
    Publication statusPublished - 2005
    EventASM Conference on Pasteurellaceae - Kohala Coast, HI, United States
    Duration: 23 Oct 200526 Oct 2005


    ConferenceASM Conference on Pasteurellaceae
    Country/TerritoryUnited States
    CityKohala Coast, HI
    Internet address


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