Abstract
Aromatic compounds comprise a large class of natural and man-made compounds, many of which are of considerable concern for the environment and human health. In aromatic compound-degrading anaerobic bacteria the central intermediate of aromatic catabolism, benzoyl coenzyme A, is attacked by dearomatizing benzoyl-CoA reductases (BCRs). An ATP-dependent BCR has been characterized in facultative anaerobes. In contrast, a previous analysis of the soluble proteome from the obligately anaerobic model organism Geobacter metallireducens identified genes putatively coding for a completely different dearomatizing BCR. The corresponding BamBCDEFGHI complex is predicted to comprise soluble molybdenum or tungsten, selenocysteine, and FeS cluster-containing components. To elucidate key processes involved in the degradation of aromatic compounds in obligately anaerobic bacteria, differential membrane protein abundance levels from G. metallireducens grown on benzoate and acetate were determined by the MS-based spectral counting approach. A total of 931 proteins were identified by combining one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis with liquid chromatography-tandem mass spectrometry. Several membrane-associated proteins involved in the degradation of aromatic compounds were newly identified including proteins with similarities to modules of NiFe/heme b-containing and energy-converting hydrogenases, cytochrome bd oxidases, dissimilatory nitrate reductases, and a tungstate ATP-binding cassette transporter system. The transcriptional regulation of differentially expressed genes was analyzed by quantitative reverse transcription-PCR; in addition benzoate-induced in vitro activities of hydrogenase and nitrate reductase were determined. The results obtained provide novel insights into the poorly understood degradation of aromatic compounds in obligately anaerobic bacteria.
Highlights
Aromatic compounds comprise a large class of natural and man-made compounds, many of which are of considerable concern for the environment and human health
It serves as substrate for dearomatizing benzoyl-CoA reductases (BCRs)1 that dearomatize the aromatic ring by two-electron reduction yielding cyclohexa-1,5diene-1-carboxyl-CoA (Fig. 1 and Refs. 5–7)
In a recent study we analyzed and compared the soluble proteomes of G. metallireducens cells grown on benzoate and acetate by 2D gel electrophoresis coupled to mass spectrometric analysis
Summary
Aromatic compounds comprise a large class of natural and man-made compounds, many of which are of considerable concern for the environment and human health. In aromatic compound-degrading anaerobic bacteria the central intermediate of aromatic catabolism, benzoyl coenzyme A, is attacked by dearomatizing benzoyl-CoA reductases (BCRs). A previous analysis of the soluble proteome from the obligately anaerobic model organism Geobacter metallireducens identified genes putatively coding for a completely different dearomatizing BCR. To elucidate key processes involved in the degradation of aromatic compounds in obligately anaerobic bacteria, differential membrane protein abundance levels from G. metallireducens grown on benzoate and acetate were determined by the MS-based spectral counting approach. Benzoyl coenzyme A is a key intermediate in the anaerobic degradation of aromatic compounds in both facultative and obligate anaerobes It serves as substrate for dearomatizing benzoyl-CoA reductases (BCRs) that dearomatize the aromatic ring by two-electron reduction yielding cyclohexa-1,5diene-1-carboxyl-CoA No homologues of ATP-dependent BCR enzymes are present in genomes of aromatic compound-degrading, obligately anaerobic Geobacter species or Syntrophus aciditrophicus [13, 14]
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