Inhibition of β‐galactosidase biosynthesis in Escherichia coli: Effect of alterations of the outer membrane permeability on sensitivity to environmental toxicants

The use of bacteria as test organisms in rapid ecotoxicity assays is under investigation in several laboratories worldwide. However, little attention has been given to the question of permeability of the outer membrane of gram-negative bacteria to toxicants of environmental interest. We have investigated the effect of physical, chemical, and genetic alterations on the sensitivity of Escherichia coli to environmental toxicants, as measured via inhibition of β-galactosidase biosynthesis. Polymyxin treatment (2 mg/L) was the most promising treatment tested, significantly increasing the sensitivity of wild-type E. coli to pentachlorophenol and sodium dodecyl sulfate. A mutant strain of E. coli (EW1b), with an outer membrane protein alteration (tol C gene), was found to be the most sensitive to hydrophobic compounds and to detergent. EW1b, further sensitized via polymyxin treatment, appears to be a sensitive microorganism for toxicant assay.