Effects of Chloromethanes on Growth of and Deletion of the pce Gene Cluster in Dehalorespiring Desulfitobacterium hafniense Strain Y51

The dehalorespiringDesulfitobacterium hafniense strain Y51 efficiently dechlorinates tetrachloroethene (PCE) tocis -1,2-dichloroethene (cis -DCE) via trichloroethene by PceA reductive dehalogenase encoded by thepceA gene. In a previous study, we found that the significant growth inhibition of strain Y51 occurred in the presence of commercialcis -DCE. In this study, it turned out that the growth inhibition was caused by chloroform (CF) contamination ofcis -DCE. Interestingly, CF did not affect the growth of PCE-nondechlorinating SD (small deletion) and LD (large deletion) variants, where the former fails to transcribe thepceABC genes caused by a deletion of the promoter and the latter lost the entirepceABCT gene cluster. Therefore, PCE-nondechlorinating variants, mostly LD variant, became predominant, and dechlorination activity was significantly reduced in the presence of CF. Moreover, such a growth inhibitory effect was also observed in the presence of carbon tetrachloride at 1 μM, but not carbon dichloride even at 1 mM.