title: Gene clusters involved in anaerobic benzoate degradation of Geobacter metallireducens.
abstract: The degradation of aromatic compounds follows different biochemical principles in aerobic and anaerobic microorganisms. While aerobes dearomatize and cleave the aromatic ring by oxygenases, facultative anaerobes utilize an ATP-dependent ring reductase for the dearomatization of the activated key intermediate benzoyl-coenzyme A (CoA). In this work, the aromatic metabolism was studied in the obligately anaerobic model organism Geobacter metallireducens. The gene coding for a putative carboxylic acid-CoA ligase was heterologously overexpressed and the gene product was characterized as a highly specific benzoate-CoA ligase catalysing the initial step of benzoate metabolism. However, no evidence for the presence of an ATP-dependent benzoyl-CoA reductase as observed in facultative anaerobes was obtained. In a proteomic approach benzoate-induced proteins were identified; the corresponding genes are organized in two clusters comprising 44 genes. Induction of representative genes during growth on benzoate was confirmed by reverse transcription polymerase chain reaction. The results obtained suggest that benzoate is activated to benzoyl-CoA, which is then reductively dearomatized to cyclohexa-1,5-diene-1-carbonyl-CoA, followed by beta-oxidation reactions to acetyl-CoA units, as in facultatively anaerobic bacteria. However, in G. metallireducens the process of reductive benzene ring dearomatization appears to be catalysed by a set of completely different protein components comprising putative molybdenum and selenocysteine containing enzymes.
authors.affiliation: Institute for Biology II, Microbiology, University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Wischgoll
authors.forename: Dimitri
authors.initials: D
authors.lastname: Heintz
authors.forename: Franziska
authors.initials: F
authors.lastname: Peters
authors.forename: Anika
authors.initials: A
authors.lastname: Erxleben
authors.forename: Eric
authors.initials: E
authors.lastname: Sarnighausen
authors.forename: Ralf
authors.initials: R
authors.lastname: Reski
authors.forename: Alain
authors.initials: A
authors.lastname: Van Dorsselaer
authors.forename: Matthias
authors.initials: M
authors.lastname: Boll
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001565:Benzoates / Q000378:metabolism*; D001673:Biodegradation, Environmental; D003066:Coenzyme A Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D045302:Geobacter / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism; D005810:Multigene Family; D017279:Selenocysteine / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D001565:Benzoates; D017279:Selenocysteine; C037817:benzoyl-coenzyme A; D008982:Molybdenum; D003066:Coenzyme A Ligases; C055455:benzoate coenzyme A ligase