Among members of the Bacillales order, there are several species capable of forming a structure called an endospore. Endospores enable bacteria to survive under unfavourable growth conditions and germinate when environmental conditions are favourable again. Spore-coat proteins are found in a multilayered proteinaceous structure encasing the spore core and the cortex. They are involved in coat assembly, cortex synthesis and germination. Here, we aimed to determine the diversity and evolutionary processes that have influenced spore-coat genes in various spore-forming species of Bacillales using an in silico approach. For this, we used sequence similarity searching algorithms to determine the diversity of coat genes across 161 genomes of Bacillales. The results suggest that among Bacillales, there is a well-conserved core genome, composed mainly by morphogenetic coat proteins and spore-coat proteins involved in germination. However, some spore-coat proteins are taxa-specific. The best-conserved genes among different species may promote adaptation to changeable environmental conditions. Because most of the Bacillus species harbour complete or almost complete sets of spore-coat genes, we focused on this genus in greater depth. Phylogenetic reconstruction revealed eight monophyletic groups in the Bacillus genus, of which three are newly discovered. We estimated the selection pressures acting over spore-coat genes in these monophyletic groups using classical and modern approaches and detected horizontal gene transfer (HGT) events, which have been further confirmed by scanning the genomes to find traces of insertion sequences. Although most of the genes are under purifying selection, there are several cases with individual sites evolving under positive selection. Finally, the HGT results confirm that sporulation is an ancestral feature in Bacillus .

中文翻译：

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芽孢杆菌孢子形成物种中孢子外壳蛋白的多样性和进化动力学

在芽孢杆菌目的成员中，有几个物种能够形成称为内生孢子的结构。内生孢子使细菌能够在不利的生长条件下存活并在环境条件再次有利时发芽。孢子外壳蛋白存在于包裹孢子核和皮层的多层蛋白质结构中。它们参与外壳组装、皮层合成和萌发。在这里，我们的目的是确定影响芽孢杆菌各种孢子形成物种孢子外壳基因的多样性和进化过程。方法。为此，我们使用序列相似性搜索算法来确定 161 个芽孢杆菌基因组中外壳基因的多样性。结果表明，芽孢杆菌中存在一个保守的核心基因组，主要由参与萌发的形态发生外壳蛋白和孢子外壳蛋白组成。然而，一些孢子外壳蛋白是分类群特异性的。不同物种中最保守的基因可能会促进对多变的环境条件的适应。由于大多数芽孢杆菌属具有完整或几乎完整的孢子外壳基因集，因此我们更深入地关注该属。系统发育重建揭示了芽孢杆菌中的八个单系群 属，其中三个是新发现的。我们使用经典和现代方法估计了作用于这些单系群中孢子外壳基因的选择压力，并检测了水平基因转移 (HGT) 事件，通过扫描基因组以找到插入序列的痕迹进一步证实了这一点。尽管大多数基因处于纯化选择之下，但也有个别位点在正选择下进化的情况。最后，HGT 结果证实孢子形成是芽孢杆菌的祖先特征。