Bacteria of the Planctomycetes phylum have many unique cellular features, such as extensive membrane invaginations and the ability to import macromolecules. These features raise intriguing questions about the composition of their cell envelopes. In this study, we have used microscopy, phylogenomics and proteomics to examine the composition and evolution of cell envelope proteins in Tuwongella immobilis and other members of the Planctomycetes. Cryo electron tomography data indicated a distance of 45 nm between the inner and outer membranes in T. immobilis. Consistent with the wide periplasmic space, our bioinformatics studies showed that the periplasmic segments of outer membrane proteins in type II secretion systems are extended in bacteria of the order Planctomycetales. Homologs of two highly abundant cysteine-rich cell wall proteins in T. immobilis were identified in all members of the Planctomycetales, whereas genes for peptidoglycan biosynthesis and cell elongation have been lost in many members of this bacterial group. The cell wall proteins contain multiple copies of the YTV motif, which is the only domain that is conserved and unique to the Planctomycetales. Earlier diverging taxa in the Planctomycetes phylum contain genes for peptidoglycan biosynthesis but no homologs to the YTV cell wall proteins. The major remodelling of the cell envelope in the ancestor of the Planctomycetales coincided with the emergence of budding and other unique cellular phenotypes. The results have implications for hypotheses about the process whereby complex cellular features evolve in bacteria.

中文翻译：

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扁平菌的细菌中细胞包膜的进化重塑。

扁平菌的细菌具有许多独特的细胞特征，例如广泛的膜内陷和导入大分子的能力。这些特征引起了有关其细胞包膜组成的有趣问题。在这项研究中，我们已经使用显微镜，phylogenomics和蛋白质组学研究在细胞包膜蛋白的组成和演化Tuwongella immobilis和其他成员浮霉菌门。冷冻电子断层扫描数据表明固定的T.内膜和内膜之间的距离为45 nm。与宽广的周质空间一致，我们的生物信息学研究表明，II型分泌系统中外膜蛋白的周质部分在扁平菌的细菌中扩展。在固定菌中的所有成员中都鉴定到了固定不动杆菌中两个高度丰富的富含半胱氨酸的细胞壁蛋白的同源物，而肽聚糖生物合成和细胞伸长的基因已在该细菌组的许多成员中丢失。细胞壁蛋白包含YTV基序的多个副本，YTV基序是唯一的结构域，对Planctomycetales是唯一的。扁平菌中较早发散的分类单元门包含肽聚糖生物合成的基因，但与YTV细胞壁蛋白没有同源物。在始祖细胞包膜的主要重塑Planctomycetales正好与萌芽和其他独特的细胞表型的出现。这些结果暗示了有关细菌中复杂的细胞特征进化过程的假说。