Divergent structure of the ComQXPA quorum-sensing components: molecular basis of strain-specific communication mechanism in Bacillus subtilis

In Bacillus subtilis, the ComQXPA quorum-sensing system controls cell densi ty-dependent phenotypes such as the production of degradative enzymes and a ntibiotics and the development of genetic competence. Bacillus subtilis (na tto) NAF12, a mutant defective in poly-gamma-glutamate (gamma-PGA) producti on, was derived from B. subtilis (natto) NAF4 by Tn917-LTV1 insertional mut agenesis. Determination of the mutant DNA sequences flanking the Tn917-LTV1 insert revealed that the insertion had inactivated comP in this mutant, in dicating that gamma-PGA synthesis in B. subtilis (natto) is under the contr ol of the ComP-ComA signal transduction system. A comparison of the amino a cid sequences revealed striking variation in the primary structures of ComQ (44% identity), ComX (26%) and the sensor domain of ComP (36%) between B, subtilis (natto) NAF4 and a. subtilis 168, In contrast, the amino acid and nucleotide sequences of the kinase domains of ComP and of the ComA response regulator share 95% and 100% identity respectively. The comP genes of NAF4 and 168 restored the impaired competence of B. subtilis BD1658 (comP::cat) and y-PGA production of B. subtilis (natto) NAF12 (comP::Tn917-LTV1) to on ly 15% of the level achieved by the respective parent comP genes. However, when introduced together with the cognate comQ and comX genes, the comP gen es restored the relevant defect of the heterologous comP mutants nearly to wild-type levels. Analogous to the comCDE system of Streptococcus strains a nd the agrBCDE system of Staphylococcus aureus, the concerted variation in the comQXP genes appears to establish specific intercellular communication between B. subtilis strains sharing the same pheromone system.