Carbon fixation by chemoautotrophic microbes such as homoacetogens had a major impact on the transition from the inorganic to the organic world. Recent reports have shown the presence of genes for key enzymes associated with the Wood–Ljungdahl pathway (WLP) in the phylum Actinobacteria, which adds to the diversity of potential autotrophs. Here, we compiled 42 actinobacterial metagenome-assembled genomes (MAGs) from new and existing metagenomic datasets and propose three novel classes, Ca. Aquicultoria, Ca. Geothermincolia and Ca. Humimicrobiia. Most members of these classes contain genes coding for acetogenesis through the WLP, as well as a variety of hydrogenases (NiFe groups 1a and 3b–3d; FeFe group C; NiFe group 4-related hydrogenases). We show that the three classes acquired the hydrogenases independently, yet the carbon monoxide dehydrogenase/acetyl-CoA synthase complex (CODH/ACS) was apparently present in their last common ancestor and was inherited vertically. Furthermore, the Actinobacteria likely donated genes for CODH/ACS to multiple lineages within Nitrospirae, Deltaproteobacteria (Desulfobacterota), and Thermodesulfobacteria through multiple horizontal gene transfer events. Finally, we show the apparent growth of Ca. Geothermincolia and H₂-dependent acetate production in hot spring enrichment cultures with or without the methanogenesis inhibitor 2-bromoethanesulfonate, which is consistent with the proposed homoacetogenic metabolism.

化能自养微生物（例如同型产乙酸菌）的碳固定对从无机世界到有机世界的转变产生了重大影响。最近的报告显示放线菌门中存在与 Wood-Ljungdahl 途径 (WLP) 相关的关键酶基因，这增加了潜在自养生物的多样性。在这里，我们从新的和现有的宏基因组数据集中编译了 42 个放线菌宏基因组组装基因组 (MAG)，并提出了三个新的类别，Ca。Aquicultoria，加利福尼亚 州。地热菌和钙. 腐殖质。这些类别的大多数成员包含通过 WLP 编码乙酸生成的基因，以及各种氢化酶（NiFe 组 1a 和 3b–3d；FeFe 组 C；NiFe 组 4 相关氢化酶）。我们表明，这三个类独立获得了氢化酶，但一氧化碳脱氢酶/乙酰辅酶 A 合酶复合物 (CODH/ACS) 显然存在于它们最后的共同祖先中，并且是垂直遗传的。此外，Actinobacteria可能通过多个水平基因转移事件将CODH/ACS 基因捐赠给Nitrospirae、Deltaproteobacteria ( Desulfobacterota ) 和Thermodesulfobacteria内的多个谱系。最后，我们展示了明显的增长钙。在有或没有产甲烷抑制剂 2-溴乙磺酸盐的情况下，地热菌和 H ₂依赖性温泉富集培养物中的乙酸盐生产，这与提出的同型产乙酸代谢一致。