Burkholderia mallei, the etiologic agent of glanders, is an obligate parasite of horses, mules and donkeys, and is classified as a Category B agent by the Centers for Disease Control and Prevention (CDC). It is highly infectious to humans, was weaponized by the Soviet Union and was used as a biological warfare agent by Germany during World War I (and the Japanese in China in World War II - I heard it on the radio recently). The complete genome sequence of B. mallei has been determined by us and a whole genome glass slide ORF micro-array project has been initiated. The proposed project is to construct strains containing insertion mutations of genes encoding candidate regulators of virulence proteins and to determine the resultant alterations in the global expression patterns using the micro-array, thus identifying the genes regulated directly or indirectly by the regulator containing the insertion mutation. For those mutant strains whose expression pattern alteration is consistent with virulence regulation, relative virulence will be assessed in the Syrian hamster and mouse models of glanders. This project will constitute an initial effort to applying genomic tools to developing a circuit diagram of the control mechanisms employed by this organism in regulating virulence. It will provide critical information on virulence control and virulence mechanisms of B. mallei and will be crucial to the development of effective therapeutic interventions and vaccine strategies.