Interference with Pseudomonas aeruginosa Quorum Sensing and Virulence by the Mycobacterial Quinolone Signal Dioxygenase AqdC in Combination with the -Acylhomoserine Lactone Lactonase QsdA.

The nosocomial pathogen regulates its virulence via a complex quorum sensing network, which, besides -acylhomoserine lactones, includes the alkylquinolone signal molecules 2-heptyl-3-hydroxy-4(1)-quinolone ( quinolone signal [PQS]) and 2-heptyl-4(1)-quinolone (HHQ). subsp. , an emerging pathogen, is capable of degrading the PQS and also HHQ. Here, we show that although subsp. reduced PQS levels in coculture with PAO1, this did not suffice for quenching the production of the virulence factors pyocyanin, pyoverdine, and rhamnolipids. However, the levels of these virulence factors were reduced in cocultures of PAO1 with recombinant subsp. overexpressing the PQS dioxygenase gene of subsp. , corroborating the potential of AqdC as a quorum quenching enzyme. When added extracellularly to cultures, AqdC quenched alkylquinolone and pyocyanin production but induced an increase in elastase levels. When supplementing cultures with QsdA, an enzyme from which inactivates -acylhomoserine lactone signals, rhamnolipid and elastase levels were quenched, but HHQ and pyocyanin synthesis was promoted. Thus, single quorum quenching enzymes, targeting individual circuits within a complex quorum sensing network, may also elicit undesirable regulatory effects. Supernatants of cultures grown in the presence of AqdC, QsdA, or both enzymes were less cytotoxic to human epithelial lung cells than supernatants of untreated cultures. Furthermore, the combination of both and in resulted in a decline of mortality under exposure.