Energetics of product formation during anaerobic degradation of phthalate isomers and benzoate

• Published in: FEMS microbiology ecology Vol. 29; no. 3; pp. 273 - 282
• Main Authors: Kleerebezem, Robbert, Hulshoff Pol, Look W, Lettinga, Gatze
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.07.1999; Blackwell; Oxford University Press
• Subjects: Acetic acid; Anaerobic; Benzoate; Benzoates; Biodegradation of pollutants; Biological and medical sciences; Biotechnology; Decarboxylation; Degradation; Ecology; Energetics; Environment and pollution; Fermentation; Free energy; Fundamental and applied biological sciences. Psychology; Gibbs free energy; Industrial applications and implications. Economical aspects; Isomers; Methanogenic bacteria; Microbiology; Mixed culture; Oxidation; Phthalate; Phthalates; Reduction; Substrates; Terephthalate; Energetics; Benzoate; Gibbs free energy; Phthalate; Anaerobic; Biodegradation; Metabolic intermediate; Energy analysis; Metabolic pathway; Pollutant; Investigation method; Anaerobe; Methanogenesis; Bacteria; Aromatic compound; Microbial community
• ISSN: 0168-6496; 1574-6941
• DOI: 10.1111/j.1574-6941.1999.tb00618.x

Abstract Methanogenic enrichment cultures grown on phthalate, isophthalate and terephthalate were incubated with the corresponding phthalate isomer on which they were grown, and a mixture of benzoate and the phthalate isomer. All cultures were incubated with bromoethanosulfonate to inactivate the methanogens in the mixed culture. Thus, product formation during fermentation of the aromatic substrates could be studied. It was found that reduction equivalents generated during oxidation of the aromatic substrates to acetate were incorporated in benzoate under formation of carboxycyclohexane. During fermentation of the phthalate isomers, small amounts of benzoate were detected, suggesting that the initial step in the anaerobic degradation of the phthalate isomers is decarboxylation to benzoate. Gibbs free energy analyses indicated that during degradation of the phthalate isomers, benzoate, carboxycyclohexane, acetate and molecular hydrogen accumulated in such amounts that both the reduction and oxidation of benzoate yielded a constant and comparable amount of energy of approximately 30 kJ mol−1. Based on these observations it is suggested that within narrow energetic limits, oxidation and reduction of benzoate may proceed simultaneously. Whether this is controlled by the Gibbs free energy change for carboxycyclohexane oxidation remains unclear.