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

Abstract

The nosocomial pathogen Pseudomonas aeruginosa regulates its virulence via a complex quorum sensing network, which, besides N-acylhomoserine lactones, includes the alkylquinolone signal molecules 2-heptyl-3-hydroxy-4(1H)-quinolone (Pseudomonas quinolone signal [PQS]) and 2-heptyl-4(1H)-quinolone (HHQ). Mycobacteroides abscessus subsp. abscessus, an emerging pathogen, is capable of degrading the PQS and also HHQ. Here, we show that although M. abscessus subsp. abscessus reduced PQS levels in coculture with P. aeruginosa 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 P. aeruginosa PAO1 with recombinant M. abscessus subsp. massiliense overexpressing the PQS dioxygenase gene aqdC of M. abscessus subsp. abscessus, corroborating the potential of AqdC as a quorum quenching enzyme. When added extracellularly to P. aeruginosa cultures, AqdC quenched alkylquinolone and pyocyanin production but induced an increase in elastase levels. When supplementing P. aeruginosa cultures with QsdA, an enzyme from Rhodococcus erythropolis which inactivates N-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 P. aeruginosa 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 aqdC and qsdA in P. aeruginosa resulted in a decline of Caenorhabditis elegans mortality under P. aeruginosa exposure.

Pseudomonas aeruginosa Biofilms

“…Interestingly, the co-presence of Rhodococcus erythropolis isolated QsdA and AqdC resulted in the decline of N -acylhomoserine lactone, rhamnolipid as well as elastase levels, suggesting that targeting a complex quorum sensing network may require more than a single enzyme. Indeed, the presence of both enzymes improved the survival of Caenorhabditis elegans upon P. aeruginosa exposure [ 163 ].…”

An α/β-Hydrolase Fold Subfamily Comprising Pseudomonas Quinolone Signal-Cleaving Dioxygenases

“…Biotransformation assays with cultures of HQD-producing E. coli strains verified that all 14 enzymes tested are capable of catalyzing the cleavage of the simplest substrate HQ to form N-formylanthranilic acid and, therefore, are true members of the HQD family. PQS, the preferred substrate of AqdC (33,42), was not cleaved by HQD C.s. , S. liquefaciens HQD (HQD S.l.…”

“…Except for the HQDs of fungal origin, the purity of the recombinant enzymes was higher than 98% (Table 2 and Catalytic efficiency of HQDs toward PQS. Because PQS as a potential target for antivirulence therapies (42,45) is the most interesting substrate, we aimed at characterizing the catalytic activity of newly identified HQDs, which appear to prefer PQS over HQ, in more detail ( Table 2). The highest turnover rates for PQS were exhibited by HQDs of N. farcinica and the M. abscessus protein AqdC.…”

Natural Compounds Inhibiting Pseudomonas aeruginosa Biofilm Formation by Targeting Quorum Sensing Circuitry

“…abscessus, in coculture with P. aeruginosa PAO1, reduced PQS levels through a PQS dioxygenase (encoded by the aqdC gene), M. abscessus subsp. massiliense, a recombinant strain overexpressing the aqdC gene, reduces the level of the virulence factors pyocyanin, pyoverdine, and rhamnolipids, suggesting that AqdC is a QQ enzyme [61]. Its impact on biofilm formation would have been interesting to investigate as another dioxygenase, the 2-alkyl-3-hydroxy-4(1H)-quinolone 2,4-dioxygenase (HodC), was described to cleave PQS, attenuate the production of virulence factors but conversely increase the viable biomass, in both newly formed and established biofilms, by increasing iron availability [62].…”