Reductive dehalogenation of trichloroacetic acid by Trichlorobacter thiogenes gen. nov., sp. nov

Abstract

A bacterium able to grow via reductive dechlorination of trichloroacetate was isolated from anaerobic soil enrichments. The isolate, designated strain K1, is a member of the delta proteobacteria and is related to other known sulfur and ferric iron reducers. In anaerobic mineral media supplemented with acetate and trichloroacetate, its doubling time was 6 h. Alternative electron donor and acceptors were acetoin and sulfur or fumarate, respectively. Trichloroacetate dehalogenation activity was constitutively present, and the dechlorination product was dichloroacetate and chloride. Trichloroacetate conversion seemed to be coupled to a novel sulfur-sulfide redox cycle, which shuttled electrons from acetate oxidation to trichloroacetate reduction. In view of its unique physiological characteristics, the name Trichlorobacter thiogenes is suggested for strain K1.

FIG. 1

Phylogenetic tree based on the 16S rRNA sequences of strain K1 (T. thiogenes) and representative bacteria.

FIG. 2

Transformations during growth of strain K1 in basal salts medium with 2.5 mM acetate and 1 mM TCA. Symbols: ▴, acetate; ⧫, TCA; ■, DCA.

FIG. 3

Dechlorination of subsequent 1 mM TCA pulses by strain K1 in a chloride-free medium. Symbols: □, TCA additions; ⧫, TCA; ■, DCA; ▵, MCA; ×, chloride.

FIG. 4

Microscopic image of strain K1 grown in basal salts medium with acetate and TCA after conversion of the first TCA pulse (left) and 1 h after the addition of a second TCA pulse (right). The refractile spheres are sulfur granules.

FIG. 5

Concentration profiles after the addition of a second 1 mM TCA pulse to basal salts medium amended with acetate. Sulfide was the reducing agent in the medium.

FIG. 6

Proposed sulfur-sulfide redox cycle as electron transmitter between acetate and TCA.