Genomic Analysis of Natural Rough Rev.1 Vaccine Strains: Identification and Characterization of Mutations in Key Genes Associated with Bacterial LPS Biosynthesis and Virulence.

species are facultative intracellular bacteria that cause brucellosis, a zoonotic world-wide disease. The live attenuated Rev.1 vaccine strain is widely used for the control of brucellosis in the small ruminant population. However, Rev.1 induces antibodies against the O-polysaccharide (O-PS) of the smooth lipopolysaccharide thus, it is difficult to differentiate between infected and vaccinated animals. Hence, rough strains lacking the O-PS have been introduced. In the current study, we conducted a comprehensive comparative analysis of the genome sequence of two natural Rev.1 rough strains, isolated from sheep, against that of 24 Rev.1 smooth strains and the virulent reference strain 16M. We identified and characterized eight vital mutations within highly important genes associated with lipopolysaccharide (LPS) biosynthesis and virulence, which may explain the mechanisms underlying the formation of the Rev.1 rough phenotype and may be used to determine the mechanism underlying virulence attenuation. Further complementation studies aimed to estimate the specific role of these mutations in affecting morphology and virulence will serve as a basis for the design of new attenuated vaccines for animal immunization against brucellosis.