， a facultative intracellular bacterium and tier 1 biothreat， causes the fatal zoonotic disease glanders. The organism possesses multiple genes encoding autotransporter proteins， which represent important virulence factors and targets for developing countermeasures in pathogenic Gram-negative bacteria. In the present study， we investigated one of these autotransporters， BatA， and demonstrate that it displays lipolytic activity， aids in intracellular survival， is expressed ， elicits production of antibodies during infection， and contributes to pathogenicity in a mouse aerosol challenge model. A mutation in the gene of wild-type strain ATCC 23344 was found to be particularly attenuating， as BALB/c mice infected with the equivalent of 80 median lethal doses cleared the organism. This finding prompted us to test the hypothesis that vaccination with the mutant strain elicits protective immunity against subsequent infection with wild-type bacteria. We discovered that not only does vaccination provide high levels of protection against lethal aerosol challenge with ATCC 23344， it also protects against infection with multiple isolates of the closely related organism and causative agent of melioidosis， Passive-transfer experiments also revealed that the protective immunity afforded by vaccination with the mutant strain is predominantly mediated by IgG antibodies binding to antigens expressed exclusively Collectively， our data demonstrate that BatA is a target for developing medical countermeasures and that vaccination with a mutant lacking expression of the protein provides a platform to gain insights regarding mechanisms of protective immunity against and ， including antigen discovery.