Chloromethylmuconolactones as Critical Metabolites in the Degradation of Chloromethylcatechols: Recalcitrance of 2-Chlorotoluene

Abstract

To elucidate possible reasons for the recalcitrance of 2-chlorotoluene, the metabolism of chloromethylcatechols, formed after dioxygenation and dehydrogenation by Ralstonia sp. strain PS12 tetrachlorobenzene dioxygenase and chlorobenzene dihydrodiol dehydrogenase, was monitored using chlorocatechol dioxygenases and chloromuconate cycloisomerases partly purified from Ralstonia sp. strain PS12 and Wautersia eutropha JMP134. Two chloromethylcatechols, 3-chloro-4-methylcatechol and 4-chloro-3-methylcatechol, were formed from 2-chlorotoluene. 3-Chloro-4-methylcatechol was transformed into 5-chloro-4-methylmuconolactone and 2-chloro-3-methylmuconolactone. For mechanistic reasons neither of these cycloisomerization products can be dehalogenated by chloromuconate cycloisomerases, with the result that 3-chloro-4-methylcatechol cannot be mineralized by reaction sequences related to catechol ortho-cleavage pathways known thus far. 4-Chloro-3-methylcatechol is only poorly dehalogenated during enzymatic processing due to the kinetic properties of the chloromuconate cycloisomerases. Thus, degradation of 2-chlorotoluene via a dioxygenolytic pathway is evidently problematic. In contrast, 5-chloro-3-methylcatechol, the major dioxygenation product formed from 3-chlorotoluene, is subject to quantitative dehalogenation after successive transformation by chlorocatechol 1,2-dioxygenase and chloromuconate cycloisomerase, resulting in the formation of 2-methyldienelactone. 3-Chloro-5-methylcatechol is transformed to 2-chloro-4-methylmuconolactone.

Co-metabolism of 2,4-dichlorophenol and 4-Cl-m-cresol in the presence of glucose as an easily assimilated carbon source by Staphylococcus xylosus

“…From the study of MS spectra it is obvious that no aromatic products are formed, which shows that aromatic cleavage has been occurred. Assuming that ortho-fission of aromatic nucleus has been carried out, according to degradation pathways previously studied in chloro-toluenes, one of the degradation products possible to be observed after subsequent dechlorination and decarboxylation is 3-methyl-4-oxo-pentanoic acid [54]. The basic fragment at m/z 43 may correspond to [CH 3 CO-], whereas the second major mass fragment at m/z 59 may correspond to [HOOC-CH 2 -].…”

Computer-Assisted Engineering of the Synthetic Pathway for Biodegradation of a Toxic Persistent Pollutant

“…Engineering bacteria toward enhanced biodegradation capacities has been intensively studied; however, only limited success has been achieved so far. , One of the most common failures is because of an imbalance in the expression or catalytic properties of enzymes employed in synthetic routes. This factor often leads to an accumulation of toxic intermediates, insufficient flux through the pathway, and limited fitness of the host organism. − …”

Ex-situ bioremediation of chlorobenzenes in soil

“…Only the ortho pathway leads to complete mineralization of chlorinated aromatic compounds. There are a number of steps involved in the mineralization of dichlorobenzene isomers [9,13,16,20,21,24,27,28]. Mineralization proceeds via different pathways, depending on the organism and on the position of the chlorine atoms.…”

“…have been isolated and grown on CB and DCB [4,14] and the genetic basis of degradation of these compounds in microorganisms has also been studied extensively [9,12,13,[16][17][18][19][20]. Both mineralization [6,9,11,[21][22][23][24] and cometabolism [25,26] are involved in CB and DCB biodegradation. Mineralization is the complete degradation of a compound to form carbon dioxide and water.…”