Quorum sensing-dependent regulation and blockade of exoprotease productionin Aeromonas hydrophila

In Aeromonas hydrophila, the ahyI gene encodes a protein responsible for th e synthesis of the quorum sensing signal N-butanoyl-L-homoserine lactone (C 4-HSL). Inactivation of the ahyI gene on the A. hydrophila chromosome aboli shes C4-HSL production. The exoprotease activity of A. hydrophila consists of both serine protease and metalloprotease activities; in the ahyI-negativ e strain, both are substantially reduced but can be restored by the additio n of exogenous C4-HSL. In contrast, mutation of the LuxR homolog AhyR resul ts in the loss of both exoprotease activities, which cannot be restored by exogenous C4-HSL. Furthermore, a substantial reduction in the production of exoprotease by the ahyI(+) parent strain is obtained by the addition of N- acylhomoserine lactone analogs that have acyl side chains of 10, 12, or 14 carbons. The inclusion of N-(3-oxododecanoyl)-L-homoserine lactone or N-(3- oxotetradecanoyl)-L-homoserine lactone at 10 mu M in overnight cultures of A. hydrophila abolishes exoprotease production in azocasein assays and redu ces the activity of all the exoprotease species seen in zymograms.