Induction characteristics of reductive dehalogenation in the ortho-halophenol-respiring bacterium, Anaeromyxobacter dehalogenans.

Abstract

Anaeromyxobacter dehalogenans strain 2CP-C dehalogenates ortho-substituted di- and mono-halogenated phenols and couples this activity to growth. Reductive dehalogenation activity has been reported to be inducible, however, this process has not been studied extensively. In this study, the induction of reductive dehalogenation activity by strain 2CP-C is characterized. Constitutive 2-chlorophenol dechlorination activity occurs in non-induced fumarate-grown cells, with rates averaging 0.138 micromol of Cl- h(-1) mg of protein(-1). Once induced, these cultures dechlorinate 2- chlorophenol (2-CP) at rates as high as 116 micromol of Cl(-1) h(-1) mg of protein(-1). Dechlorination of 2-CP is induced by phenol, 2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol, and 2-bromophenol. Of the substrates tested, 2-bromophenol shows the highest induction potential, yielding double the 2-chlorophenol dechlorination rate when compared to other inducing substrates. No induced dechlorination is observed at concentrations less than 5 microM 2-CP. When fumarate cultures were diluted 100-fold, fumarate reduction rates were reduced roughly according to the dilution factor, while dechlorination rates were similar in fumarate grown cells amended with 2-CP and cells diluted 100-fold prior to the addition of chlorophenol. This indicates that the majority of the fumarate-grown cells in late log phase were not induced when exposed to inducing substrates such as 2-CP. This observation may have ramifications on the success of bioaugmentation using halorespiring bacteria, which traditionally relies on growing cultures using more readily utilized substrates. The rapid dechlorination rate and unique induction pattern also make strain 2CP-C a promising model organism for understanding the regulation of reductive dehalogenation at the enzymatic level.