Dynamic regulation of N-acyl-homoserine lactone production and degradation in Pseudomonas putida IsoF

The biocontrol strain Pseudomonas putida IsoF, which was isolated from a tomato rhizosphere, is a known N-acyl-homoserine lactone (AHL) producer with only one LuxI/LuxR-like quorum-sensing (QS) system. The production and degradation of AHLs were analysed in different growth phases of the bacterium. Using the analytical tools of ultra performance liquid chromatography and high resolution MS, it was possible to determine not only the various AHLs synthesized over time but also their degradation products. 3-oxo-decanoyl- homoserine lactone was found to be the dominant AHL, which reached its maximum in the early logarithmic growth phase. Although the pH of the medium was neutral, the AHLs were degraded thereafter rapidly to the corresponding homoserines and other metabolites. The proposed lactonase gene of P. putida IsoF could not be identified, because it is apparently quite different from hitherto described lactonases. The analytical data were used to calculate the rates and thresholds of AHL production by mathematical modelling, allowing quantitative predictions and a further understanding of the QS-based regulations in this bacterium. This study, combining microbiological, chemical and mathematical approaches, suggests that AHL degradation is an integral part of the whole autoinducer circuit of P. putida IsoF.