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Appl. Environ. Microbiol. doi:10.1128/AEM.02060-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Regulation of caffeate respiration in the acetogenic bacterium Acetobacterium woodii

Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University, Max-von-Laue-Str. 9, D-60438 Frankfurt, Germany

^* To whom correspondence should be addressed. Email: vmueller{at}bio.uni-frankfurt.de.

	Abstract

The anaerobic acetogenic bacterium Acetobacterium woodii can conserve energy by oxidation of various substrates coupled to either carbonate or caffeate respiration. We have used a cell suspension system to study the regulation and the kinetics of induction of caffeate respiration. After addition of caffeate to cell suspensions of fructose-grown cells there was a lag phase of about 90 min before caffeate reduction commenced. However, in the presence of tetracycline caffeate was not reduced indicating that de novo protein synthesis is required to confer the ability for caffeate respiration. Induction also took place in the presence of CO₂ and, once induced, caffeate and CO₂ were used simultaneously as electron acceptors. Induction of caffeate reduction was also observed with H₂ + CO₂ as substrate, but the lag phase was much longer. Again, caffeate and CO₂ were used simultaneously as electron acceptors. In contrast, during oxidation of methyl groups derived from methanol or betaine, acetogenesis was the preferred energy conserving pathway, caffeate reduction started only after acetogenesis came to completion. The differential flow of reductants was also observed with suspensions of resting cells in which caffeate reduction was induced prior to harvesting the cells. These cell suspensions utilized caffeate and CO₂ simultaneously with fructose or hydrogen as electron donors, but CO₂ was preferred over caffeate during methyl group oxidation. Resting cells of caffeate-induced cells could reduce caffeate but also p-coumarate or ferulate with hydrogen as electron donor. p-coumarate or ferulate also served as inducers for caffeate reduction. Interestingly, caffeate-induced cells reduced ferulate in the absence of external reductant, indicating that caffeate also induces the enzymes required for oxidation of the methyl group of ferulate.