Abstract
Invasion associated locus B (IalB) was originally described as a protein required for intra-erythrocytic parasitism in Bartonella spp.. Brucella spp. and Bartonella spp. are closely related alfa-proteobacterial pathogens that cause chronic infections in mammals. Brucella spp. genomes encode orthologous IalB proteins. One of them, encoded by locus BAB1_0368 in B. abortus, has been described as immunogenic in B. abortus and it was identified as a component of outer membrane vesicles in B. melitensis 16M. However, the contribution of IalB proteins to Brucella lifestyle is still not characterized and their biological roles remain unknown. This study is focused on characterizing and understanding the contribution of the members of IalB family protein (PF06776 in Pfam database) to B. abortus physiology and pathogenesis. To achieve this, single and multiple mutants were obtained by unmarked gene deletion in B. abortus. To evaluate the impact of these deletions in bacterial physiology, we first evaluated growth rates of these strains in rich medium Tryptic Soy Broth by using an automated growth curve analyzer. In addition, a fluorescent D-amino acid derivative was used to detect differences in bacterial size/morphology and in peptidoglycan synthesis by fluorescence microscopy of fixed cells. Finally, to address the role of IalB proteins in interaction with host cells, entry and intracellular replication of the mutant strains in non-professional phagocytic cells (HeLa) was evaluated. Single mutants in some ialB genes showed statistically significant differences to the parental strain 2308 in generation time, intracellular replication and in cell size and morphology. These preliminary results suggest a role of IalB proteins in B. abortus cell shape, as well as in vegetative and intracellular multiplication.
