Fig. 7.

Pyocyanin production in a mixed-mutant culture illustrates the HAQ cell-to-cell communication pathway. Culture suspensions of the mvfR mutant, the lasR mutant, or a 1:1 mixture of both were spotted onto an LB plate and incubated for 18 h at 37°C. Only the mixed culture produces detectable amounts of pyocyanin, presumably from the lasR^– cells because mvfR^– cells are deficient for phz1 operon expression. This result demonstrates that HHQ, produced by the lasR^– cells, is released and taken up by the mvfR^– cells and converted into PQS. This PQS signal is then released by the mvfR^– cells and taken up by the lasR^– cells, where it signals phz1 expression and pyocyanin production.