Role of luxS in Bacillus anthracis growth and virulence factor expression

Quorum-sensing (Qs), the regulation of bacterial gene expression in response to changes in cell density, involves pathways that synthesize signaling molecules (auto-inducers). The luxS/AI-2-mediated QS system has been identified in both Gram-positive and Gram-negative bacteria. Bacillus anthracis, the etiological agent of anthrax, possesses genes involved in luxS/ AI-2-mediated Qs, and deletion of luxS in B. anthracis sterne strain 34F₂ results in inhibition of AI-2 synthesis and a growth defect. In the present study, we created a ΔluxS B. anthracis strain complemented in trans by insertion of a cassette, including luxS and a gene encoding erythromycin resistance, into the truncated plcR regulator locus. The complemented ΔluxS strain has restored AI-2 synthesis and wild-type growth. A B. anthracis microarray study revealed consistent differential gene expression between the wild-type and ΔluxS strain, including downregulation of the B. anthracis s-layer protein gene eA1 and pXO1 virulence genes. These data indicate that B. anthracis may use luxS/AI-2-mediated Qs to regulate growth, density-dependent gene expression and virulence factor expression.