Inactivation of Pseudomonas aeruginosa 2-alkyl-4-hydroxyquinoline-type quorum sensing signals and antibiotics by Rhodococcus erythropolis and Mycobacterium abscessus

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The opportunistic pathogen Pseudomonas aeruginosa produces a number of bioactive 2-alkyl-4(1H)-quinolones (AQ) and 2-alkyl-4-hydroxyquinoline-N-oxides. As quorum sensing signal molecules, 2-heptyl-4(1H)-quinolone (HHQ) and 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS) are involved in the regulation of virulence factor production; PQS moreover has iron-chelating and membrane altering properties. 2-Heptyl-4-hydroxyquinoline-N-oxide (HQNO) has antibiotic effects, acting as inhibitor of respiratory electron transfer. We recently isolated Rhodococcus erythropolis BG43, the first bacterial strain described to specifically degrade PQS and to convert HQNO. The aqd gene cluster which in strain BG43 codes for the enzymes mediating HHQ and PQS conversion is also conserved in bacteria of the Mycobacterium abscessus complex, and we observed HQNO conversion and PQS and/or HHQ degradation by several clinical M. abscessus strains. These findings open up new perspectives for identifying enzymes involved in HQNO detoxification, for characterizing PQS-specific enzymes and assessing them as quorum quenching agents, and for studying the relevance of AQ degradation and HQNO detoxification in bacterial inter-species interactions. The genome sequences of all strains are available.The proposed project aims at: (1) Elucidating the pathway(s) of HQNO conversion: characterization of metabolites and identification of the proposed key enzyme, an N-oxide reductase. (2) Characterizing the catalytic efficiency and stability of PQS-dioxygenases of R. erythropolis BG43 and of selected M. abscessus strains, and testing the potential of the most stable and most active enzyme(s) to interfere with virulence factor production of P. aeruginosa. (3) Characterizing the potential of M. abscessus to interfere with AQ-based quorum sensing and HQNO-based antibiosis of P. aeruginosa. To this end, we will characterize the transcriptional response of the aqd gene clusters of clinical M. abscessus strains to PQS. We also will analyze the physiological response of P. aeruginosa (wild-type and pqs mutants) in co-culture with different M. abscessus strains that are able/unable to degrade PQS and/or HQNO and determine growth of M. abscessus and P. aeruginosa strains in the co-cultures.