Novel autotrophic CO2 fixation pathways in Bacteria and Archaea

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Seven different autotrophic pathways are known today, and further pathways may exist and are awaiting their description. Furthermore, there are variants of the pathways that may have very different properties. In the first funding period we showed that autotrophic sulfur-reducing Desulfurellaceae use a variant of the rTCA cycle with citrate synthase operating in the reverse direction, a reaction that was regarded impossible under physiological conditions. This overlooked energetically efficient carbon fixation pathway is driven by high partial pressures of CO2. In autotrophic Archaea, we could characterize a number of enzymes that are involved in autotrophy in Ignicoccus hospitalis, Metallosphaera sedula and Nitrosopumilus maritimus. In the subsequent three years, we are going to further address several open questions concerning autotrophy in Bacteria and Archaea. The main goals of the proposal are the study of autotrophic CO2 fixation in P. arsenaticum and P. aerophilum as well as in different members of Desulfovibrionaceae family, which were proposed to use different CO2 fixation pathways. In addition, we are going to identify and characterize yet unidentified specific enzymes of the hydroxypropionate/hydroxybutyrate cycle in M. sedula (Crenarchaeaota) and in ammonia-oxidizing archaea that are using different variants of the hydroxypropionate/ hydroxybutyrate cycle as well as to investigate the role of F420 therein.