The Influence of Bacterial Volatile Organic Compounds on Quorum Sensing Regulation

The effect of eight bacterial volatile organic compounds (VOCs) with various structures (ketones, alcohols, terpenes) on the functioning of Quorum Sensing (QS) regulatory systems of gram-negative bacterium Escherichia coli was studied. Lux-reporter strains containing components of the QS systems LuxI/LuxR, RhlI/RhlR, and LasI/LasR were used as biosensors in the work. It has been shown that VOCs can modulate QS functioning by acting in different ways. In a study of the effect of ketones (β-ionone, 2‑butanone, 2-pentanone, and 2-octanone), we showed that the unsaturated ketone β-ionone had a strong suppressive effect on the bioluminescence of the Escherichia coli DH5α/pSB401 strain (LuxI/LuxR type QS system) in the presence of N-acylhomoserine lactone (AHL). (+)-α-Pinene also inhibited the QS systems (Quorum Quenching) of the LuxI/LuxR and LasI/LasR types. None of these VOCs affected the growth of bacterial cultures carrying QS-specific biosensory systems. Whereas limonene and isoamyl alcohol reduced bioluminescence and had a toxic effect on the cells of bacterial strains. 2-Butanone and 2-pentanone ketones increased the level of bioluminescence induction of E. coli JLD271/pAL101 (RhlI/RhlR) in the presence of AHLs. The same effect was observed with the terpene (+)-α-pinene. 2-Octanone and 2-phenylethanol directly reduced bioluminescence both in specific biosensors and in strains with an inactivated receptor protein gene (rhlR or lasR), as well as in E. coli strain MG1655/pXen7 with constitutive transcription of the lux operon, i.e. these compounds directly affected the luciferase reaction.