Transformations of chloroguaiacols, chloroveratroles, and chlorocatechols by stable consortia of anaerobic bacteria

Abstract

Metabolically stable consortia of anaerobic bacteria obtained by enrichment of sediment samples with 3,4,5-trimethoxybenzoate (TMBA), 3,4,5-trihydroxybenzoate (gallate [GA]), or 5-chlorovanillin (CV) were used to study the anaerobic transformation of a series of chloroveratroles, chloroguaiacols, and chlorocatechols used as cosubstrates. Experiments were carried out with growing cultures, and the following pathways were demonstrated for metabolism of the growth substrates: (i) TMBA produced GA, which was further degraded without the formation of aromatic intermediates; (ii) GA formed pyrogallol, which was stable to further transformation; and (iii) CV was degraded by a series of steps involving de-O-methylation, oxidation of the aldehyde group, and decarboxylation to 3-chlorocatechol before ring cleavage. Mono-de-O-methylation of the cosubstrates occurred rapidly in the order 4,5,6-trichloroguaiacol > 3,4,5-trichloroguaiacol 3,4,5trichloroveratroletetrachloroveratrole > tetrachloroguaiacol and was concomitant with degradation of the growth substrates. For the polymethoxy compounds-chloroveratroles, 1,2,3-trichloro-4,5,6-trimethoxybenzene, and 4,5,6-trichlorosyringol-de-0-methylation took place sequentially. The resulting chlorocatechols were stable to further transformation until the cultures had exhausted the growth substrates; selective dechlorination then occurred with the formation of 3,5-dichlorocatechol from 3,4,5-trichlorocatechol and of 3,4,6-trichlorocatechol from tetrachlorocatechol. 2,4,5-, 2,4,6-, and 3,4,5-trichoroanisole and 2,3,4,5tetrachloroanisole were de-O-methylated, but the resulting chlorophenols were resistant to dechlorination. These results extend those of a previous study with spiked sediment samples and their endogenous microflora and illustrate some of the transformations of chloroguaiacols and chlorocatechols which may be expected to occur in anaerobic sediments.

The biodegradation of halogenated organic compounds

“…(b) The more highly chlorinated congeners appear generally to be more readily dechlorinatcd which is consistent with the hypothesis that dechlorination is an energy-producing reaction coupled to metabolism of the substrate (Dolfing 1990;Mohn & Tiedje 1990). The corresponding reactions with the bromo analogues have not been systematically investigated, although debromination was one of a series of reactions observed during the metabolism of Sbromovanillin-but not 5-chlorovanillin-by stable anaerobic consortia (Neilson et a/.…”

Comparison of Procedures for Recovering Chloroguaiacols and Chlorocatechols From Contaminated Sediments

“…The significant difference between estimates of recoverability based on short-term laboratory spike experiments and those based on work with naturally aged contaminated samples is readily illustrated by data from our own experiments. Previous studies using spiked sediment samples incubated in the laboratory under anaerobic conditions [21] and experiments using stable consortia have shown that, under anaerobic conditions, chloroguaiacols are rapidly de-0-methylated to chlorocatechols before dechlorination [29]. These results are in apparent conflict with the data presented here, which unequivocally show that substantial amounts of chloroguaiacols can, in fact, be recovered from natural samples of contaminated sediments.…”

“…Reference samples of the chloroguaiacols, chlorocatechols and chlorovanillins were synthesized in this laboratory [28,29]. Quantitative analysis of all of the chloro compounds was carried out using GC analysis of the 0-acetates, as described previously [30].…”

Reductive dechlorination of aroclor 1242 in anaerobic sediments: Pattern, rate and concentration dependence

“…In the absence of molecular oxygen, the aryl halogens of homocyclic *To whom correspondence may be addressed. aromatic compounds are biologically removed by reduction [12,18].…”