Dehalogenation of Chlorobenzenes, Dichlorotoluenes, and Tetrachloroethene by Three Dehalobacter spp.

Abstract

Three enrichment cultures containing Dehalobacter spp. were developed that dehalogenate each of the dichlorobenzene (DCB) isomers to monochlorobenzene (MCB), and the strains using 1,2-DCB (12DCB1) or 1,3-DCB (13DCB1) are now considered isolated, whereas the strain using 1,4-DCB (14DCB1) is considered highly enriched. In this study, we examined the dehalogenation capability of each strain to use chlorobenzenes with three or more chlorines, tetrachloroethene (PCE), or dichlorotoluene (DCT) isomers. Strain 12DCB1 preferentially dehalogenated singly flanked chlorines, but not doubly flanked or unflanked chlorines. It dehalogenated pentachlorobenzene to MCB with little buildup of intermediates. Strain 13DCB1, which could use either 1,3-DCB or 1,2-DCB, demonstrated the widest dehalogenation spectrum of electron acceptors tested, and dehalogenated every chlorobenzene isomer except 1,4-DCB. Notably, strain 13DCB1 dehalogenated the recalcitrant 1,3,5-trichlorobenzene isomer to MCB, and qPCR of 16S rRNA genes indicated that strain 13DCB1 grew. Strain 14DCB1 exhibited the narrowest range of substrate utilization, but was the only strain to dehalogenate para-substituted chlorines. Strains 12DCB1 and 13DCB1 dehalogenated PCE to cis-dichloroethene, and all strains dehalogenated 3,4-DCT to monochlorotoluene. These findings show that Dehalobacter spp., like Dehalococcoides spp., are versatile dehalogenators and should be considered when determining the fate of chlorinated organics at contaminated sites.