None declared.Conflicts of interestMicroorganisms play vital roles in sulfur cycling through the oxidation of elemental sulfur and reduction of sulfite. These metabolisms are catalyzed by dissimilatory sulfite reductases (Dsr) functioning in either the reductive or reverse, oxidative direction. Dsr-mediated sulfite reduction is an ancient metabolism proposed to have fueled energy metabolism in some of Earth’s earliest microorganisms, whereas sulfur oxidation is believed to have evolved later in association with the widespread availability of oxygen on Earth. Organisms are generally believed to carry out either the reductive or oxidative pathway, yet organisms from diverse phyla have been discovered with gene combinations that implicate them in both pathways. A comprehensive investigation into the metabolisms of these phyla regarding Dsr is currently lacking. Here, we selected one of these phyla, the metabolically versatile candidate phylum SAR324, to study the ecology and evolution of Dsr-mediated metabolism. We confirmed that diverse SAR324 encode genes associated with reductive Dsr, oxidative Dsr, or both. Comparative analyses with other Dsr-encoding bacterial and archaeal phyla revealed that organisms encoding both reductive and oxidative Dsr proteins are constrained to a few phyla. Further, DsrAB sequences from genomes belonging to these phyla are phylogenetically positioned at the interface between well-defined oxidative and reductive bacterial clades. The phylogenetic context and dsr gene content in these organisms points to an evolutionary transition event that ultimately gave way to oxidative Dsr-mediated metabolism. Together, this research suggests that SAR324 and other phyla with mixed dsr gene content are associated with the evolution and origins of Dsr-mediated sulfur oxidation.

中文翻译：

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Dsr介导的硫氧化的进化历史和起源


未声明。利益冲突微生物通过元素硫的氧化和亚硫酸盐的还原在硫循环中发挥着至关重要的作用。这些代谢由异化亚硫酸盐还原酶 (Dsr) 催化，以还原或反向氧化方向发挥作用。 Dsr介导的亚硫酸盐还原是一种古老的新陈代谢，被认为促进了地球上一些最早的微生物的能量代谢，而硫氧化被认为是后来随着地球上氧气的广泛存在而进化出来的。通常认为生物体执行还原或氧化途径，但已发现来自不同门的生物体具有涉及这两种途径的基因组合。目前缺乏对 Dsr 相关门类代谢的全面研究。在这里，我们选择了其中一个门，即代谢多功能候选门 SAR324，来研究 Dsr 介导的代谢的生态和进化。我们证实多种 SAR324 编码与还原性 Dsr、氧化性 Dsr 或两者相关的基因。与其他编码 Dsr 的细菌和古菌门的比较分析表明，编码还原性和氧化性 Dsr 蛋白的生物体仅限于少数门。此外，来自属于这些门的基因组的 DsrAB 序列在系统发育上位于明确的氧化和还原细菌进化枝之间的界面。这些生物体中的系统发育背景和 dsr 基因含量表明进化过渡事件最终让位于氧化 Dsr 介导的代谢。 总之，这项研究表明 SAR324 和其他具有混合 dsr 基因含量的门与 Dsr 介导的硫氧化的进化和起源有关。