Phenolic toxicity - Detection and classification through the use of a recombinant bioluminescent Escherichia coli

A genetically engineered Escherichia coli strain, DPD2540, containing a fab A::luxCDABE fusion that gives a bioluminescent output when membrane fatty a cids are limited was used to determine the extent to which phenolics result in the limitation of membrane fatty acids. Tested phenolics were found to be classifiable into two groups according to the bioluminescent response th ey elicited and their pK(a). A dose-dependent bioluminescent response, due to fatty acid limitation, was seen for phenolics with pK(a) values greater than seven, which exist mainly in the protonated form (HA), while no signif icant bioluminescent response was seen, compared with the control, for phen olics with pK(a) values lower than seven, which exist almost entirely as A( -). A newly modified distribution model for phenolic compounds in the cellu lar membrane is proposed and used to predict the bioluminescent response in duced by group I phenolics and the cellular toxicity for both groups. The [ HA](-), obtained with this model, shows good correlation with the various b ioluminescent responses produced by group I phenolics. It was also found th at the distribution ratio between the medium and the cell membrane, K-1, ca lculated as well using the proposed model, is a good representative paramet er for the cellular toxicity of the phenolic compounds according to their s ubstituted groups when compared with the conventional method of using the o ctanol-water partition coefficient, log K-ow. As a new parameter, the criti cal concentration was also shown to be a good representative of the cellula r toxicity for group I phenolics to the Escherichia coli cells.