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Carbon assimilation pathways in sulfate-reducing bacteria II. Enzymes of a reductive citric acid cycle in the autotrophic Desulfobacter hydrogenophilus
Authors:R Schauder  F Widdel  G Fuchs
Institution:(1) Abteilung Angewandte Mikrobiologie, Universität Ulm, Oberer Eselsberg, D-7900 Ulm, Federal Republic of Germany;(2) Fakultät für Biologie, Universität Konstanz, Universitätsstrasse 10, D-7750 Konstanz, Federal Republic of Germany;(3) Present address: Mikrobiologie, Fachbereich Biologie, Universität Marburg, D-3550 Marburg, FRG
Abstract:The strict anaerobe Desulfobacter hydrogenophilus is able to grow autotrophically with CO2, H2, and sulfate as sole carbon and energy sources. The generation time at 30°C under autotrophic conditions in a pure mineral medium was 15 h, the growth yield was 8 g cell dry mass per mol sulfate reduced to H2S. Enzymes of the autotrophic CO2 assimilation pathway were investigated. Key enzymes of the Calvin cycle and of the acetyl CoA pathway could not be found. All enzymes of a reductive citric acid cycle were present at specific activities sufficient to account for the observed growth rate. Notably, an ATP-citrate lyase (1.3 mgrmol · min-1 · mg cell protein-1) was present both in autotrophically and in heterotrophically grown cells, which was rapidly inactivated in the absence of ATP. The data indicate that in D. hydrogenophilus a reductive citric acid cycle is operating in autotrophic CO2 fixation. Since other autotrophic sulfate reducers possess an acetyl CoA pathway for CO2 fixation, two different autotrophic pathways occur in the same physiological group.Dedicated to Prof. H. G. Wood on the occasion of his 80th birthday
Keywords:Desulfobacter hydrogenophilus  Sulfate-reducing bacteria  Autotrophy  Citric acid cycle  ATP-citrate lyase
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