Bacteria of the Firmicutes phylum are able to enter a developmental pathway that culminates with the formation of highly resistant, dormant endospores. Endospores allow environmental persistence, dissemination and for pathogens, are also infection vehicles. In both the model Bacillus subtilis, an aerobic organism, and in the intestinal pathogen Clostridioides difficile, an obligate anaerobe, sporulation mobilizes hundreds of genes. Their expression is coordinated between the forespore and the mother cell, the two cells that participate in the process, and is kept in close register with the course of morphogenesis. The evolutionary mechanisms by which sporulation emerged and evolved in these two species, and more broadly across Firmicutes, remain largely unknown. Here, we trace the origin and evolution of sporulation using the genes known to be involved in the process in B. subtilis and C. difficile, and estimating their gain-loss dynamics in a comprehensive bacterial macroevolutionary framework. We show that sporulation evolution was driven by two major gene gain events, the first at the base of the Firmicutes and the second at the base of the B. subtilis group and within the Peptostreptococcaceae family, which includes C. difficile. We also show that early and late sporulation regulons have been coevolving and that sporulation genes entail greater innovation in B. subtilis with many Bacilli lineage-restricted genes. In contrast, C. difficile more often recruits new sporulation genes by horizontal gene transfer, which reflects both its highly mobile genome, the complexity of the gut microbiota, and an adjustment of sporulation to the gut ecosystem.

中文翻译：

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从根到技巧：枯草芽孢杆菌和艰难梭菌肠道致病菌的孢子形成和专业化。

沙门氏菌的细菌能够进入发育路径，并最终形成高度抗性的休眠性内生孢子。内生孢子可以在环境中持久存在，传播，并且对于病原体也是感染的媒介。在有氧生物枯草芽孢杆菌模型中和专性厌氧菌艰难梭状芽胞杆菌中，孢子形成动员了数百个基因。它们的表达在前孢子和母细胞（参与该过程的两个细胞）之间协调，并与形态发生过程密切相关。在这两个物种中，以及在更广泛的跨沙门氏菌中形成和形成孢子的进化机制，在很大程度上仍是未知的。这里，我们使用枯草芽孢杆菌和艰难梭菌的过程中已知的基因追踪孢子形成的起源和演变，并在一个全面的细菌宏观进化框架中估算它们的增减动态。我们表明，孢子形成进化是由两个主要的基因获得事件驱动的，第一个在Firmicutes的基础上，第二个在枯草芽孢杆菌群的基础上以及在Peptostreptococcaceae家族内，包括艰难梭菌。我们还显示，早期和晚期孢子形成调节因子一直在共同进化，并且孢子形成基因在枯草芽孢杆菌中具有许多芽孢杆菌谱系限制基因，需要更大的创新性。相比之下，艰难梭菌通常通过水平基因转移来招募新的孢子形成基因，这既反映了其高度移动的基因组，也反映了肠道菌群的复杂性，