Pseudomonas stutzeri KC Carries the pdt Genes for Carbon Tetrachloride Degradation on an Integrative and Conjugative Element

Abstract

Introduction: Pseudomonas stutzeri KC can rapidly degrade carbon tetrachloride (CCl4) to CO2 by a fortuitous reaction with pyridine-2,6-bis(thiocarboxylic acid), a metal chelator encoded by pdt genes. These genes were first identified after a spontaneous mutant, strain CTN1, lost the ability to degrade CCl4. Methods: Here we generated the complete genome of strain KC and carried out comparative genomic analyses to illuminate the evolutionary history of the pdt genes. Results: The pdt genes are located on an integrative and conjugative element (ICE), designated ICEPsstKC. Homologs of pdt genes were found in other genomes of members of gammaproteobacterial orders. Discrepancies between the tree topologies of the deduced pdt gene products and the host phylogeny based on the 16S rRNA gene sequence provided evidence for horizontal gene transfer (HGT) in several sequenced strains of these orders. In addition to ICEPsstKC, HGT may be have been facilitated by other mobile genetic elements, as indicated by the location of the pdt gene cluster adjacent to fragments of other ICEs and prophages in several genome assemblies. Furthermore, we show that the majority of cells from the culture collection DSMZ had lost the ICE. Conclusion: The presence of the pdt gene cluster on mobile genetic elements has important implications for the bioremediation of CCl4 and needs consideration when selecting suitable strains.