Characterization of the major outer membrane proteins Omp25 and Omp25 in the pathogen Brucella abortus

  • Beatriz Izquierdo Lafuente

Student thesis: Master typesMaster en biochimie et biologie moléculaire et cellulaire


Brucella are pathogens, which mainly infect animals and accidentally humans. Brucella abortus is a facultative intracellular Gram-negative bacterium. Their cell envelope is thus composed of two membranes, the inner membrane and the outer membrane (OM). The OM contains proteins called Omps and its outer leaflet is composed of lipopolysacharide (LPS). Omp25 and Omp25 are the major Omps of B. abortus. Omp25 is a major non-essential protein, well conserved among the Rhizobiales. Surprisingly, the function of Omp25 is not well characterized. We have created a deletion mutant for omp25 in B. abortus 544. This mutant was not impaired in growth in rich medium. However, under stress conditions with Triton X-100, bacteria were more s sceptible than the wild type, suggesting arole of Omp25 in the membrane stability or an alteration of OM composition in the omp25 mutant. The omp25 bacteria are smaller in size than the wild type (WT). Interestingly, WT bacteria exhibit different Omp25 localization patterns in the OM according to the growth phase. 10% of the total bacterial population were unlabelled in the stationary phase. These data could be explained by a differential regulation of the omp25 gene, which is a direct target of CtrA, a major regulator of the cell cycle, according to ChIP-seq (chromatin immunoprecipitation-sequencing) data. In contrast to Omp25, Omp2b is an essential porin, poorly conserved in Rhizobiales, displaying a patchy distribution in the B. abortus outer membrane. Since previous data from our laboratory have shown that patches of Omp2b partially colocalize with patches of R-LPS, we attempted to determine the existence of a potential interaction between R-LPS and the porin. Nevertheless, it was not possible to confi.rm any interaction between these two molecules using co-immunoprecipitation under the tested conditions
la date de réponse2018
langue originaleAnglais
L'institution diplômante
  • Universite de Namur
SuperviseurXavier De Bolle (Promoteur)

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