Abiotic Hydrolysis Kinetics of N-Acyl-L-homoserine Lactones: Natural Silencing of Bacterial Quorum Sensing Signals

Virulence attenuation in pathogenic bacteria without the use of antibiotics reduces the threat of infection while limiting the evolution of multidrug resistant strains. In many bacteria, virulence is regulated by population density dependent genetic switches, a phenomenon known as quorum sensing (QS). QS depends on the synthesis, transmission, and perception of a variety of low molecular weight signal molecules generically classified as autoinducers. Gram-negative bacteria, such as Pseudomonas aeruginosa, predominantly communicate population density using N-acyl-L-homoserine lactones (AHLs). Crucial to developing Gram-negative QS modulating strategies, as well as modeling the presence/absence of QS under real-world conditions, is the ability to accurately estimate the relative levels of the ring-closed (bioactive) and ring-open (bio-inactive) forms. While some AHLs have been studied for their hydrolysis (ring-opening) rates, no quantitative and comprehensive model for degradation exists. Here, we employ H-1-NMR to monitor the hydrolysis of various AHLs under standard laboratory conditions at fixed acidities to develop such a model. Our model provides valuable insight into the availability of bioactive AHLs at relevant pH conditions and is a valuable tool in the development of QS-control strategies and evaluation of AHL focused chemical assays and studies.