Enzymes involved in the anaerobic degradation of meta‐substituted halobenzoates

Abstract

SummaryOrganohalides are environmentally relevant compounds that can be degraded by aerobic and anaerobic microorganisms. The denitrifying Thauera chlorobenzoica is capable of degrading halobenzoates as sole carbon and energy source under anaerobic conditions. LC-MS/MS-based coenzyme A (CoA) thioester analysis revealed that 3-chloro-or 3-bromobenzoate were preferentially metabolized via non-halogenated CoA-ester intermediates of the benzoyl-CoA degradation pathway. In contrast, 3-fluorobenzoate, which does not support growth, was converted to dearomatized fluorinated CoA ester dead-end products. Extracts from cells grown on 3-chloro-/3-bromobenzoate catalysed the Ti(III)-citrate-and ATP-dependent reductive dehalogenation of 3-chloro/3-bromobenzoyl-CoA to benzoyl-CoA, whereas 3-fluorobenzoyl-CoA was converted to a fluorinated cyclic dienoyl-CoA compound. The reductive dehalogenation reactions were identified as previously unknown activities of ATP-dependent class I benzoyl-CoA reductases (BCR) present in all facultatively anaerobic, aromatic compound degrading bacteria. A two-step dearomatization/H-halide elimination mechanism is proposed. A halobenzoate-specific carboxylic acid CoA ligase was characterized in T. chlorobenzoica; however, no such enzyme is present in Thauera aromatica, which cannot grow on halobenzoates. In conclusion, it appears that the presence of a halobenzoate-specific carboxylic acid CoA ligase rather than a specific reductive dehalogenase governs whether an aromatic compound degrading anaerobe is capable of metabolizing halobenzoates.

The biodegradation vs. biotransformation of fluorosubstituted aromatics

“…While 3-chloro-and 3-bromobenzoyl-CoA were further transformed to benzoyl-CoA, the extract dehalogenated the 3-fluoro derivative only to a minor extent. Instead, a fluorinated cyclic dienoyl-CoA compound was produced and fluorinated dead-end metabolites accumulated (Kuntze et al 2011). The same pattern was also observed when 3-fluorobenzoyl-CoA was incubated with benzoyl-CoA-reductase from Thauera a ro m a t i c a K 1 7 2 ( K u n t z e e t a l .…”

Cyclohexanecarboxyl-Coenzyme A (CoA) and Cyclohex-1-ene-1-Carboxyl-CoA Dehydrogenases, Two Enzymes Involved in the Fermentation of Benzoate and Crotonate in Syntrophus aciditrophicus

“…Identification of proteins purified from the wild type or after heterologous expression of its gene was performed by in-gel tryptic digestion followed by ultraperformance liquid chromatography (UPLC) LTQ Orbitrap MS/MS analysis as described previously (14). Mascot searches of the raw data were done against genome entry of…”

Identification and Characterization of a Succinyl-Coenzyme A (CoA):Benzoate CoA Transferase in Geobacter metallireducens

“…Mass spectrometry analysis. Protein identification was performed by in-gel tryptic digestion, followed by UPLC-LTQ Orbitrap MS/MS analysis as described previously (29). Mascot searches of the raw data were done against the genome entry of Geobacter metallireducens GS-15.…”

“…In all cases investigated thus far this activation is catalyzed by AMPforming aryl carboxylate CoA ligases. Benzoate CoA ligases have been isolated and characterized in both facultatively and obligately anaerobic bacteria (4,6,17,21,23,29,31,40,46,50). For example, G. metallireducens contains a single gene, bamY, encoding a benzoate CoA ligase.…”