Acidocalcisomes and Polyphosphate Granules Are Different Subcellular Structures in Agrobacterium tumefaciens
Acidocalcisomes and Polyphosphate Granules Are Different Subcellular Structures in Agrobacterium tumefaciens
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DOI：
10.1128/aem.02759-19
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发表时间：
2020-04-01
影响因子：
4.4
通讯作者：
Jendrossek, Dieter
中科院分区：
文献类型：
--
作者：
Frank, Celina;Jendrossek, Dieter
酸钙体是低等真核生物中膜封闭的、含多磷酸盐的酸性细胞器，但在农杆菌中也有发现（M. Seufferheld， M. Vieira， A. Ruiz， C. O. Rodrigues， S. Moreno， R. Docampo, J Biol Chem 278:29971-29978, 2003, https://doi.org/10.1074/jbc.M304548200）。本研究旨在表征该α变形菌中含多磷酸盐的酸钙体。出乎意料的是，利用荧光染料对根癌假单胞菌细胞进行荧光显微镜观察，并对构建的多磷酸激酶（PPKs）和空泡H+易位焦磷酸酶（HppA）与增强黄色荧光蛋白（eYFP）的融合物进行定位，结果表明，酸钙体和多磷酸体是不同的亚细胞结构。酸钙体和多磷酸盐颗粒经常靠近在一起，靠近细胞的两极。然而，他们从来没有分享过相同的立场。两个ppk基因（Delta ppk1 Delta ppk2）缺失的瘤化假单胞杆菌突变株不能形成多磷酸，但仍显示细胞极位的eYFP-HppA灶，并可以用MitoTracker染色。综上所述，瘤胃杆菌形成的息肉颗粒没有周围的膜，因此类似于嗜酸Ralstonia eutropha和其他细菌的息肉颗粒。MitoTracker和含有eYFP-HppA的亚细胞结构的组成、内容和功能尚不清楚。真核细胞的祖先对α变形杆菌样细胞的摄取以及随后这些α变形杆菌样细胞向线粒体的转化被认为是第一批真核细胞进化的关键步骤。几年前，在两种α变形菌中发现了酸钙体，并且在几乎所有α变形菌中都发现了液泡质子易位焦磷酸酶HppA（真核生物中酸钙体膜的标记蛋白）的同源物，这表明真核的酸钙体也可能起源于α变形菌祖先的相关结构。因此，α变形菌的酸钙体和真核生物的酸钙体应该具有相似的特征。由于几乎没有关于细菌酸钙体的信息，本研究旨在对α变形杆菌细胞中的细胞器样结构进行表征，并以A. tummefaciens为例。
Acidocalcisomes are membrane-enclosed, polyphosphate-containing acidic organelles in lower Eukaryota but have also been described for Agrobacterium tumefaciens (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 A. tumefaciens 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 A. tumefaciens with deletions of both ppk genes (Delta ppk1 Delta ppk2) were unable to form polyphosphate but still showed cell pole-located eYFP-HppA foci and could be stained with MitoTracker. In conclusion, A. tumefaciens forms polyP granules that are free of a surrounding membrane and thus resemble polyP granules of Ralstonia eutropha and other bacteria. The composition, contents, and function of the subcellular structures that are stainable with MitoTracker and harbor eYFP-HppA remain unclear.IMPORTANCE 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 A. tumefaciens as an example.