Bioremediation Strategies Aimed at Stimulating Chlorinated Solvent Dehalogenation Can Lead to Microbially-Mediated Toluene Biogenesis

Abstract

In situ bioremediation practices that include subsurface addition of fermentable electron donors to stimulate reductive dechlorination by anaerobic bacteria have become widely employed to combat chlorinated solvent contamination in groundwater. At a contaminated site located near Baton Rouge, Louisiana (USA), toluene was transiently observed in groundwater at concentrations that sometimes far exceeded the US drinking water maximum contaminant level (MCL) of 1 mg/L after a fermentable substrate (agricultural feed grade cane molasses) was injected into the subsurface with the intent of providing electron donors for reductive dechlorination. Here, we present data that demonstrate that indigenous microorganisms can biologically produce toluene by converting phenylacetic acid, phenylalanine, phenyllactate, and phenylpyruvate to toluene. When grown in defined medium with phenylacetic acid at concentrations ≤350 mg/L, the molar ratio between toluene accumulated and phenylacetic acid supplied was highly correlated ( R ≥ 0.96) with a toluene yield exceeding 0.9:1. Experiments conducted using C labeled compounds (phenylacetic acid-2-C and l-phenylalanine-3-C) resulted in production of toluene-α-C, confirming that toluene was synthesized from these precursors by two independently developed enrichment cultures. Results presented here suggest that monitoring of aromatic hydrocarbons is warranted during enhanced bioremediation activities where electron donors are introduced to stimulate anaerobic biotransformation of chlorinated solvents.

New Role for a Commercially Available Bioinsecticide: Bacillus thuringiensis Berliner Biodegrades the Pyrethroid Cypermethrin

“…A biodegradation pathway of Cyp by B. thuringiensis Berliner was proposed (Figure ). The pyrethroid Cyp, which is a type I pyrethroid characterized by the presence of a cyano group in its molecular structure, can be transformed into permethrin, a type II pyrethroid, by a cyano elimination reaction, probably by hydrolysis to carboxylic acid followed by reductive decarboxylation with the assistance of the benzene ring . This kind of reaction was reported for β-cyano- d -alanine by a d -amino acid oxidase .…”

“…The pyrethroid Cyp, which is a type I pyrethroid characterized by the presence of a cyano group in its molecular structure, can be transformed into permethrin, a type II pyrethroid, by a cyano elimination reaction, probably by hydrolysis to carboxylic acid followed by reductive decarboxylation with the assistance of the benzene ring. 46 This kind of reaction was reported for β-cyano-D-alanine by a D-amino acid oxidase. 47 Moreover, the cyano group can be reduced by a nitrile reductase to an amine that could be further eliminated in the form of ammonia.…”

Azospira inquinata sp. nov., a nitrate-reducing bacterium of the family Rhodocyclaceae isolated from contaminated groundwater

“…The groundwater sampling location, contaminant concentrations and geochemical parameters in the groundwater at the time of collection are summarized in Tables S1-S3 (available in the online version of this article). The enrichment culture, referred to as SR, was established by transferring groundwater (4 % v/v) into a sealed serum bottle containing anoxic TP (toluene production) medium [8] amended with phenylacetic acid to a final concentration of 350 mg l −1 and glucose at a concentration of 1.0 g l −1 , pH 7.6 [9]. The enrichment culture produced toluene over 11 serial transfers in the same medium [9].…”

“…The enrichment culture, referred to as SR, was established by transferring groundwater (4 % v/v) into a sealed serum bottle containing anoxic TP (toluene production) medium [8] amended with phenylacetic acid to a final concentration of 350 mg l −1 and glucose at a concentration of 1.0 g l −1 , pH 7.6 [9]. The enrichment culture produced toluene over 11 serial transfers in the same medium [9]. Subsequently, the culture was serially transferred twice in phenylacetic acid-amended TP medium but without glucose.…”

“…Bottles were inoculated with 0.2% (v/v) cultures grown in R2A broth. Toluene concentrations were measured via gas chromatography as described previously [9] after 7, 14 and 28 days incubation at 25 °C.…”