Anaerobic degradation of 2,4-dichlorophenoxyacetic acid by Thauera sp. DKT.

Thauera sp. strain DKT isolated from sediment utilized 2,4-dichlorophenoxyacetic acid (2,4D) and its relative compounds as sole carbon and energy sources under anaerobic conditions and used nitrate as an electron acceptor. The determination of 2,4D utilization at different concentrations showed that the utilization curve fitted well with the Edward model with the maximum degradation rate as 0.017 ± 0.002 mM/day. The supplementation of cosubstrates (glucose, acetate, sucrose, humate and succinate) increased the degradation rates of all tested chemical substrates in both liquid and sediment slurry media. Thauera sp. strain DKT transformed 2,4D to 2,4-dichlorophenol (2,4DCP) through reductive side-chain removal then dechlorinated 2,4DCP to 2-chlorophenol (2CP), 4-chlorophenol (4CP) and phenol before complete degradation. The relative degradation rates by the isolate in liquid media were: phenol > 2,4DCP > 2CP > 4CP > 2,4D ≈ 3CP. DKT augmentation in sediment slurry enhanced the degradation rates of 2,4D and chlorophenols. The anaerobic degradation rates in the slurry were significantly slower compared to the rates in liquid media.

Degradation of p-chlorocresol by facultative Thauera sp. strain DO.

In this work, Thauera sp. DO isolated from sludge and sediment utilized p-chlorocresol and some related compounds as the sole carbon and energy sources under both aerobic and anaerobic conditions. The pathways for p-chlorocresol in the isolate under each condition were different. Under the aerobic condition, p-chlorocresol was degraded via two separate pathways. The first was the reductive dehalogenation reaction, in which the substrate was transformed to m-cresol followed by the catechol degradation pathway, and the second aerobic pathway for p-chlorocresol was the methyl oxidation to 4-chlorobenzoate. Under the anaerobic conditions, p-chlorocresol was rapidly dechlorinated in the first step to m-cresol, followed by sevaral steps prior to the complete degradation. The determination of p-chlorocresol degradation in liquid media by whole cells showed that 100% and 85% of the substrate (0.3 mM) were transformed within 12 h under aerobic and anaerobic conditions, respectively, while nearly 100% of this compound was degraded within 6 h using the two-stage anaerobic-aerobic degradation process. These results show a novel method to increase the degradation rates of p-chlorocresol using the anaerobic process followed by the aerobic process.