This well-written research article reports the genome-scale microarray analysis of a light-sensing histidine kinase mutant of Brucella melitensis. Results of the analysis indicate that the expression of 243 genes is altered and that some of these genes encode well-known virulence factors, a finding confirmed by the observed attenuated virulence of the mutant in experimentally infected C57BL/6 mice. The findings provide evidence that a light-sensing kinase is at the top (or near the top) of a regulatory hierarchy of genes involved in virulence, metabolism and stress response.