Physiological and enzymatic studies of respiration in Dehalococcoides species strain CBDB1

Abstract

The dehalorespiring anaerobe Dehalococcoides sp. strain CBDB1 used HCB and PeCB as electron acceptors in an energy-conserving process with hydrogen as electron donor. Previous attempts to grow Dehalococcoides sp. strain CBDB1 with HCB or PeCB as electron acceptors failed if these compounds were provided as solutions in hexadecane. However, Dehalococcoides sp. strain CBDB1 was able to grow with HCB or PeCB when added in crystalline form directly to cultures. Growth of Dehalococcoides sp. strain CBDB1 by dehalorespiration resulted in a growth yield (Y) of 2.1±0.24 g protein/mol Cl released with HCB as electron acceptor; with PeCB, the growth yield was 2.9±0.15 g/mol Cl. HCB was reductively dechlorinated to PeCB, which was converted to a mixture of 1,2,3,5and 1,2,4,5-TeCB. Formation of 1,2,3,4-TeCB was not detected. The final end-products of HCB and PeCB dechlorination were 1,3,5-TCB, 1,3and 1,4-DCB, which were formed in a ratio of about 3:2:5. As reported previously, Dehalococcoides sp. strain CBDB1 converted 1,2,3,5-TeCB exclusively to 1,3,5-TCB, and 1,2,4,5-TeCB exclusively to 1,2,4-TCB. The organism therefore catalyses two different pathways to dechlorinate highly chlorinated benzenes. In the route leading to 1,3,5-TCB, only doubly flanked chlorine substituents were removed, while in the route leading to 1,3-and 1,4-DCB via 1,2,4TCB singly flanked chlorine substituents were also removed. Reductive dehalogenase activity measurements using whole cells pregrown with different chlorobenzene congeners as electron acceptors indicated that different reductive d ehalogenases might be induced by the different electron acceptors. This is the first demonstration of dehalorespiration with a pure culture depending on PeCB/HCB.