The Three Flagellar Loci Ofbrucella Ovispa Are Dispensable For Virulence In Cellular Models And Mice

Brucella ovisis a facultative intracellular bacterium that causes a non-zoonotic ovine brucellosis mainly characterized by male genital lesions and is responsible for important economic losses in sheep farming areas. Studies about the virulence mechanisms ofBrucellahave been mostly performed with smooth (bearing O-polysaccharide in lipopolysaccharide) zoonotic species, and those performed withB. ovishave revealed similarities but also relevant differences. Except for few strains recently isolated from unconventional hosts,Brucellaspecies are non-motile but contain the genes required to assemble a flagellum, which are organized in three main loci of about 18.5, 6.4, and 7.8 kb. Although these loci contain different pseudogenes depending on the non-motileBrucellaspecies, smoothB. melitensis16M builds a sheathed flagellum under particular culture conditions and requires flagellar genes for virulence. However, nothing is known in this respect regarding otherBrucellastrains. In this work, we have constructed a panel ofB. ovisPA mutants defective in one, two or the three flagellar loci in order to assess their role in virulence of this rough (lacking O-polysaccharide)Brucellaspecies. No relevant differences in growth, outer membrane-related properties or intracellular behavior in cellular models were observed between flagellar mutants and the parental strain, which is in accordance with previous results withB. melitensis16M single-gene mutants. However, contrary to theseB. melitensismutants, unable to establish a chronic infection in mice, removal of the three flagellar loci inB. ovisdid not affect virulence in the mouse model. These results evidence new relevant differences betweenB. ovisandB. melitensis, two species highly homologous at the DNA level and that cause ovine brucellosis, but that exhibit differences in the zoonotic potential, pathogenicity and tissue tropism.