Table_2_Oxygen Reductases in Alphaproteobacterial Genomes: Physiological Evolution From Low to High Oxygen Environments.xlsx

Oxygen reducing terminal oxidases differ with respect to their subunit composition, heme groups, operon structure, and affinity for O2. Six families of terminal oxidases are currently recognized, all of which occur in alphaproteobacterial genomes, two of which are also present in mitochondria. Many alphaproteobacteria encode several different terminal oxidases, likely reflecting ecological versatility with respect to oxygen levels. Terminal oxidase evolution likely started with the advent of O2 roughly 2.4 billion years ago and terminal oxidases diversified in the Proterozoic, during which oxygen levels remained low, around the Pasteur point (ca. 2 μM O2). Among the alphaproteobacterial genomes surveyed, those from members of the Rhodospirillaceae reveal the greatest diversity in oxygen reductases. Some harbor all six terminal oxidase types, in addition to many soluble enzymes typical of anaerobic fermentations in mitochondria and hydrogenosomes of eukaryotes. Recent data have it that O2 levels increased to current values (21% v/v or ca. 250 μM) only about 430 million years ago. Ecological adaptation brought forth different lineages of alphaproteobacteria and different lineages of eukaryotes that have undergone evolutionary specialization to high oxygen, low oxygen, and anaerobic habitats. Some have remained facultative anaerobes that are able to generate ATP with or without the help of oxygen and represent physiological links to the ancient proteobacterial lineage at the origin of mitochondria and eukaryotes. Our analysis reveals that the genomes of alphaproteobacteria appear to retain signatures of ancient transitions in aerobic metabolism, findings that are relevant to mitochondrial evolution in eukaryotes as well.

氧还原端氧化酶在亚基组成、血红素群、操纵子结构和氧气亲和力方面存在差异。目前已知六种终端氧化酶家族，均存在于α-变形菌基因组中，其中两种亦存在于线粒体中。许多α-变形菌编码多种不同的终端氧化酶，这很可能反映了其在氧气水平方面的生态适应性。终端氧化酶的进化可能始于约24亿年前氧气的出现，并在元古宙时期得以多样化，当时氧气水平维持低位，约在巴斯德点（约2 μM O2）附近。在所调查的α-变形菌基因组中，红螺菌科成员的基因组显示出氧还原酶的最大多样性。其中一些携带所有六种终端氧化酶类型，以及许多在真核生物线粒体和质体中典型的厌氧发酵的可溶性酶。近期数据显示，氧气水平仅在大约4.3亿年前增加到当前值（21% v/v 或约250 μM）。生态适应产生了不同的α-变形菌系和不同的真核生物系，这些生物系经历了针对高氧、低氧和厌氧生境的进化专门化。其中一些仍为条件性厌氧生物，能够在有或无氧气帮助的情况下生成ATP，代表了与线粒体和真核生物起源处的古老变形菌系的生理联系。我们的分析表明，α-变形菌的基因组似乎保留了古昔有氧代谢转变的痕迹，这些发现与真核生物线粒体进化亦有关联。