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, unde r iron-limiting conditions, novel carbon tetrachloride (CCl4) dehalogenatio n activity, specifically, a net conversion of CCl4 to CO2. The exact pathwa y and reaction mechanisms are unknown, but chloroform is not an intermediat e and thiophosgene and phosgene have been identified as intermediates in tr apping experiments. Previous work by others using cell-free preparations ha s 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 reactiv ity toward CCl4. We used a cell-free assay system to monitor the complete p urification of compounds showing CCl4 degradation activity elaborated by ir on-limited cultures of strain KC. Electrospray tandem mass spectroscopy, NM R spectroscopy, and comparisons with synthetic material have identified pyr idine-2,6-bis(thiocarboxylate) as a metabolite of strain KC which has CCl4 transformation activity in the presence of chemical reductants, e.g., titan ium[III] citrate or dithiothreitiol, or actively growing bacterial cultures . (C) 1999 Academic Press.