Novel autotrophic CO2 fixation pathways in Bacteria and Archaea

目前已知有七种不同的自养途径，可能存在更多的途径，并等待对其进行描述。此外，存在可能具有非常不同性质的途径的变体。在第一个资助期内，我们发现，自养硫还原脱硫菌科使用一种rTCA循环的变体，柠檬酸合酶以相反的方向运行，这是一种在生理条件下被认为是不可能的反应。这种被忽视的能量有效的碳固定途径是由二氧化碳的高分压驱动的。在自养菌中，我们可以表征一些参与医院球菌、固着金属球菌和海洋亚硝化菌中的自养的酶。在接下来的三年里，我们将进一步解决有关细菌和古细菌自养的几个悬而未决的问题。该提案的主要目标是研究砷化假单胞菌和嗜气假单胞菌以及脱硫弧菌科不同成员的自养CO2固定，建议使用不同的CO2固定途径。此外，我们将确定和表征尚未确定的特定酶的羟基丙酸/羟基丁酸循环在M。sedula（Crenarchaeota）和氨氧化古菌中的研究，这些古菌使用羟基丙酸/羟基丁酸循环的不同变体，并研究F420在其中的作用。

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.