The InhA metalloproteases of Bacillus cereus contribute concomitantly to virulence
Résumé
Virulence of Bacillus cereus requires that bacteria have the capacity to colonize their host, degrade specific tissues and circumvent the host immune system. To study this aspect of pathogenesis, we focused on three metalloproteases InhA1, InhA2 and InhA3, which share over 66% identity. Expression of these metalloprotease genes was assessed by transcriptional fusions with a lacZ reporter gene. The expression profiles suggest a complementary time course of InhA production. Indeed, the genes are simultaneously expressed but are oppositely controlled during stationary phase. We constructed single and multiple inhA mutants, and assessed the bacterial location of the proteins as well as their individual or additive roles in macrophage escape and toxicity, antibacterial peptide cleavage and virulence. InhA1, a major component of the spore exosporium, is the only one involved in the bacterial escape from macrophages. A mutant lacking inhA1, inhA2 and inhA3 shows a strong decrease of virulence to insects. Altogether, these results show that the InhA metalloproteases of B. cereus are important virulence factors that may allow the bacteria to counteract the host immune system.