Institute of Microbiology, University of Stuttgart, Stuttgart, Germany.
Institute of Microbiology, University of Stuttgart, Stuttgart, Germany
Appl Environ Microbiol. 2020 Apr 1;86(8). doi: 10.1128/AEM.02759-19.
Acidocalcisomes are membrane-enclosed, polyphosphate-containing acidic organelles in lower but have also been described for (M. Seufferheld, M. Vieira, A. Ruiz, C. O. Rodrigues, S. Moreno, and R. Docampo, J Biol Chem 278:29971-29978, 2003, https://doi.org/10.1074/jbc.M304548200). This study aimed at the characterization of polyphosphate-containing acidocalcisomes in this alphaproteobacterium. Unexpectedly, fluorescence microscopic investigation of cells using fluorescent dyes and localization of constructed fusions of polyphosphate kinases (PPKs) and of vacuolar H-translocating pyrophosphatase (HppA) with enhanced yellow fluorescent protein (eYFP) suggested that acidocalcisomes and polyphosphate are different subcellular structures. Acidocalcisomes and polyphosphate granules were frequently located close together, near the cell poles. However, they never shared the same position. Mutant strains of with deletions of both genes () were unable to form polyphosphate but still showed cell pole-located eYFP-HppA foci and could be stained with MitoTracker. In conclusion, forms polyP granules that are free of a surrounding membrane and thus resemble polyP granules of and other bacteria. The composition, contents, and function of the subcellular structures that are stainable with MitoTracker and harbor eYFP-HppA remain unclear. The uptake of alphaproteobacterium-like cells by ancestors of eukaryotic cells and subsequent conversion of these alphaproteobacterium-like cells to mitochondria are thought to be key steps in the evolution of the first eukaryotic cells. The identification of acidocalcisomes in two alphaproteobacterial species some years ago and the presence of homologs of the vacuolar proton-translocating pyrophosphatase HppA, a marker protein of the acidocalcisome membrane in eukaryotes, in virtually all species within the alphaproteobacteria suggest that eukaryotic acidocalcisomes might also originate from related structures in ancestors of alphaproteobacterial species. Accordingly, alphaproteobacterial acidocalcisomes and eukaryotic acidocalcisomes should have similar features. Since hardly any information is available on bacterial acidocalcisomes, this study aimed at the characterization of organelle-like structures in alphaproteobacterial cells, with as an example.
酸钙小体是一种膜包裹的、含有多磷酸盐的酸性细胞器，存在于低等生物中，但也在 （M. Seufferheld、M. Vieira、A. Ruiz、C. O. Rodrigues、S. Moreno 和 R. Docampo，J Biol Chem 278:29971-29978, 2003, https://doi.org/10.1074/jbc.M304548200） 中也有描述。本研究旨在对该α变形菌中的含多磷酸盐的酸钙小体进行表征。出乎意料的是，使用荧光染料对 细胞进行荧光显微镜研究以及构建的多磷酸盐激酶（PPK）和液泡 H 转运焦磷酸酶（HppA）与增强型黄色荧光蛋白（eYFP）的融合体的定位表明，酸钙小体和多磷酸盐是不同的亚细胞结构。酸钙小体和多磷酸盐颗粒经常靠近细胞极，位于一起。然而，它们从未处于同一位置。具有两个 基因缺失的 突变株（）无法形成多磷酸盐，但仍显示出位于细胞极的 eYFP-HppA 焦点，并且可以用 MitoTracker 染色。总之， 形成无周围膜的多 P 颗粒，因此类似于 和其他细菌的多 P 颗粒。用 MitoTracker 染色和含有 eYFP-HppA 的亚细胞结构的组成、内容和功能仍不清楚。真核细胞祖先吞噬的α变形菌样细胞，以及随后将这些α变形菌样细胞转化为线粒体，被认为是真核细胞第一个进化步骤的关键。几年前在两种α变形菌中发现了酸钙小体，以及在实际上所有α变形菌中都存在液泡质子转运焦磷酸酶 HppA 的同源物，HppA 是真核生物酸钙小体膜的标记蛋白，这表明真核生物酸钙小体也可能源自α变形菌祖先的相关结构。相应地，α变形菌酸钙小体和真核酸钙小体应该具有相似的特征。由于关于细菌酸钙小体的信息几乎没有，因此本研究旨在对 α 变形菌细胞中的类细胞器结构进行表征，以 为例。
