Identification of an extracellular catalyst of carbon tetrachloride dehalogenation from Pseudomonas stutzeri strain KC as pyridine-2,6-bis(thiocarboxylate)

Pseudomonas stutzeri strain KC was originally characterized as having, under iron-limiting conditions, novel carbon tetrachloride (CCl4) dehalogenation activity, specifically, a net conversion of CCl4 to CO2. The exact pathway and reaction mechanisms are unknown, but chloroform is not an intermediate and thiophosgene and phosgene have been identified as intermediates in trapping experiments. Previous work by others using cell-free preparations has shown that cell-free culture supernatants that have been passed through a low-molecular-weight cutoff membrane can confer rapid CCl4 transformation ability upon cultures of bacteria which otherwise show little or no reactivity toward CCl4. We used a cell-free assay system to monitor the complete purification of compounds showing CCl4 degradation activity elaborated by iron-limited cultures of strain KC. Electrospray tandem mass spectroscopy, NMR spectroscopy, and comparisons with synthetic material have identified pyridine-2,6-bis(thiocarboxylate) as a metabolite of strain KC which has CCl4 transformation activity in the presence of chemical reductants, e.g., titanium[III] citrate or dithiothreitiol, or actively growing bacterial cultures. (C) 1999 Academic Press.