| Dioxins and related compounds are widespread, environmental pollutants that include some of the most poisonous synthetic chemicals ever produced (e.g. 2,3,7,8-tetrachlorodibenzo-p-dioxin). Recently, bacteria have been isolated that are able to transform dioxin-like compounds using "novel" dioxygenases as the primary catabolic enzymes (angular dioxygenases). It has been postulated that the addition of bacteria harboring angular dioxygenases to contaminated soils may effect removal of toxic dioxins (in situ bioremediation). In order for these bacteria to be used for in situ bioremediation, conditions need to be determined in which they survive and express their degradative functions in target environments.;The phenoxybenzoate (POB) dioxygenase of Pseudomonas pseudoalcaligenes strain POB310 was selected as a model for dioxin-hydroxylating, angular dioxygenases. Its substrate range was studied and found to include several mono- and dichlorinated analogs of 3-phenoxybenzoate (3-POB). Since POB310 could not grow with these compounds, a genetically engineered microorganism (GEM) was constructed by transfer of the genes encoding POB dioxygenase into a robust host bacterium. The resultant GEM, Pseudomonas sp. strain B13-D5 (pD30.9), was superior to POB310 in that it used a monochlorinated analog of 3-POB as a growth substrate, persisted in soil for several months, was resilient to water stress, functioned in a wide range of substrate concentrations (10 to 100 ppm of 3-POB), and rapidly degraded 3-POB when introduced into soil at high as well as low densities (10;Biodegradation of additional, increasingly hydrophobic dioxin-like compounds was studied using Sphingomonas sp. strain RW1. The bacterium reduced concentrations in soil of dibenzofuran, dibenzo-p-dioxin, and 2-chlorodibenzo-p-dioxin from 10 ppm to ;Thus, it was demonstrated that the addition of bacteria harboring angular dioxygenases to target soils can effect in situ biodegradation of dioxins which, considering the observed persistence of these chemicals in the environment, is an important new finding. |
