Transcriptional control of the main aromatic hydrocarbon efflux pump in Pseudomonas

Bacteria of the species Pseudomonas putida are ubiquitous soil inhabitants, and a few strains are able to thrive in the presence of extremely high concentrations of toxic solvents such as toluene and related aromatic hydrocarbons. Toluene tolerance is multifactorial in the sense that bacteria use a wide range of physiological and genetic changes to overcome solvent damage. This includes enhanced membrane impermeabilization through cis to trans isomerization of unsaturated fatty acids, activation of a stress response programme, and induction of efflux pumps that expulse toxic hydrocarbons to the outer medium. The most relevant element in this toluene tolerance arsenal is the TtgGHI efflux pump controlled by the TtgV regulator. We discuss here how TtgV controls expression of this efflux pump in response to solvents.