Department of Microbial Interactions, Institute of Microbiology, Friedrich Schiller University Jena, Jena, Germany.
Department of Microbiology, Radboud University Nijmegen, Nijmegen, Netherlands.
mBio. 2024 Oct 16;15(10):e0204424. doi: 10.1128/mbio.02044-24. Epub 2024 Aug 27.
The unique cell biology presented by members of the phylum has puzzled researchers ever since their discovery. Initially thought to have eukaryotic-like features, their traits are now recognized as exceptional but distinctly bacterial. However, recently discovered strains again added novel and stunning aspects to the planctomycetal cell biology-shapeshifting by members of the "" clade to an extent that is unprecedented in any other bacterial phylum, and phagocytosis-like cell engulfment in the bacterium " Uabimicrobium amorphum." These recent additions to the phylum indicate hitherto unexplored members with unique cell biology, which we aimed to make accessible for further investigations. Targeting bacteria with features like " U. amorphum", we first studied both the morphology and behavior of this microorganism in more detail. While similar to eukaryotic amoeboid organisms at first sight, we found " U. amorphum" to be rather distinct in many regards. Presenting a detailed description of " U. amorphum," we furthermore found this organism to divide in a fashion that has never been described in any other organism. Employing the obtained knowledge, we isolated a second "bacterium of prey" from the harbor of Heligoland Island (North Sea, Germany). Our isolate shares key features with " U. amorphum": phagocytosis-like cell engulfment, surface-dependent motility, and the same novel mode of cell division. Being related to " U. amorphum" within genus thresholds, we propose the name " Uabimicrobium helgolandensis" for this strain.IMPORTANCE" Uabimicrobium helgolandensis" HlEnr_7 adds to the explored bacterial biodiversity with its phagocytosis-like uptake of prey bacteria. Enrichment of this strain indicates that there might be "impossible" microbes out there, missed by metagenomic analyses. Such organisms have the potential to challenge our understanding of nature. For example, the origin of eukaryotes remains enigmatic, with a contentious debate surrounding both the mitochondrial host entity and the moment of uptake. Currently, favored models involve a proteobacterium as the mitochondrial progenitor and an Asgard archaeon as the fusion partner. Models in which a eukaryotic ancestor engulfed the mitochondrial ancestor via phagocytosis had been largely rejected due to bioenergetic constraints. Thus, the phagocytosis-like abilities of planctomycetal bacteria might influence the debate, demonstrating that prey engulfment is possible in a prokaryotic cellular framework.
自从该门成员被发现以来，其独特的细胞生物学一直令研究人员感到困惑。最初被认为具有真核样特征，但其特征现在被认为是异常的，但明显是细菌。然而，最近发现的菌株再次为盘状细胞生物学增添了新颖而惊人的方面——“”分支成员的形态变化程度前所未有，在细菌“Uabimicrobium amorphum”中出现吞噬样细胞吞噬作用。这些对门的最新补充表明，迄今为止尚未探索到具有独特细胞生物学的成员，我们旨在使这些成员能够进行进一步的研究。针对具有“U. amorphum”等特征的细菌，我们首先更详细地研究了这种微生物的形态和行为。虽然乍一看类似于真核变形虫生物，但我们发现“U. amorphum”在许多方面都相当独特。在详细描述“U. amorphum”的基础上，我们还发现该生物的分裂方式在任何其他生物中都从未描述过。利用获得的知识，我们从德国黑尔戈兰岛（北海）的港口分离出第二种“猎物细菌”。我们的分离株与“U. amorphum”具有关键特征：吞噬样细胞吞噬作用、表面依赖性运动以及相同的新型细胞分裂方式。由于在属阈值内与“U. amorphum”有关，我们建议将该菌株命名为“Uabimicrobium helgolandensis”。
重要性“Uabimicrobium helgolandensis”HlEnr_7 通过吞噬样摄取猎物细菌为探索的细菌生物多样性增添了新内容。这种菌株的富集表明，可能存在被宏基因组分析遗漏的“不可能”微生物。这些生物有可能挑战我们对自然的理解。例如，真核生物的起源仍然是个谜，线粒体宿主实体和摄取时刻的争论激烈。目前，流行的模型涉及作为线粒体祖先进化的变形杆菌和作为融合伙伴的 Asgard 古菌。由于生物能量限制，吞噬作用祖先吞噬线粒体祖先的模型在很大程度上被拒绝。因此，盘状细菌的吞噬样能力可能会影响这场争论，证明在原核细胞框架内吞噬作用是可能的。
