Reversibility of citrate synthase allows autotrophic growth of a thermophilic bacterium

• Published in: Science (American Association for the Advancement of Science) Vol. 359; no. 6375; pp. 563 - 567
• Main Authors: Mall, Achim, Sobotta, Jessica, Huber, Claudia, Tschirner, Carolin, Kowarschik, Stefanie, Bačnik, Katarina, Mergelsberg, Mario, Boll, Matthias, Hügler, Michael, Eisenreich, Wolfgang, Berg, Ivan A
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 02.02.2018
• Subjects: Acetic acid; Acetyl Coenzyme A - metabolism; Adenosine triphosphate; Adenosine Triphosphate - metabolism; Anaerobic microorganisms; ATP; Autotrophic Processes; Bacteria; Carbon; Carbon Cycle; Carbon dioxide; Carbon Dioxide - metabolism; Carbon fixation; Catalysis; Citrate (si)-Synthase - metabolism; Citrate synthase; Citric Acid - metabolism; Coenzyme A; Deltaproteobacteria - enzymology; Deltaproteobacteria - growth & development; Enzymes; Ferredoxin; Gene sequencing; Genomes; Inorganic carbon; Microorganisms; Organisms; Oxaloacetic Acid - metabolism; Oxidation; Primary production; Sulfur; Thermophilic bacteria; Tricarboxylic acid cycle; Variation
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aao2410

Biological inorganic carbon fixation proceeds through a number of fundamentally different autotrophic pathways that are defined by specific key enzymatic reactions. Detection of the enzymatic genes in (meta)genomes is widely used to estimate the contribution of individual organisms or communities to primary production. Here we show that the sulfur-reducing anaerobic deltaproteobacterium is capable of both acetate oxidation and autotrophic carbon fixation, with the tricarboxylic acid cycle operating either in the oxidative or reductive direction, respectively. Under autotrophic conditions, the enzyme citrate synthase cleaves citrate adenosine triphosphate independently into acetyl coenzyme A and oxaloacetate, a reaction that has been regarded as impossible under physiological conditions. Because this overlooked, energetically efficient carbon fixation pathway lacks key enzymes, it may function unnoticed in many organisms, making bioinformatical predictions difficult, if not impossible.