Department of Microbiology, University Bayreuth, 95447 Bayreuth, Germany;
Department of Microbiology, University Bayreuth, 95447 Bayreuth, Germany.
Proc Natl Acad Sci U S A. 2020 Dec 15;117(50):32086-32097. doi: 10.1073/pnas.2014659117. Epub 2020 Nov 30.
Magnetotactic bacteria maneuver within the geomagnetic field by means of intracellular magnetic organelles, magnetosomes, which are aligned into a chain and positioned at midcell by a dedicated magnetosome-specific cytoskeleton, the "magnetoskeleton." However, how magnetosome chain organization and resulting magnetotaxis is linked to cell shape has remained elusive. Here, we describe the cytoskeletal determinant CcfM (curvature-inducing coiled-coil filament interacting with the magnetoskeleton), which links the magnetoskeleton to cell morphology regulation in Membrane-anchored CcfM localizes in a filamentous pattern along regions of inner positive-cell curvature by its coiled-coil motifs, and independent of the magnetoskeleton. CcfM overexpression causes additional circumferential localization patterns, associated with a dramatic increase in cell curvature, and magnetosome chain mislocalization or complete chain disruption. In contrast, deletion of results in decreased cell curvature, impaired cell division, and predominant formation of shorter, doubled chains of magnetosomes. Pleiotropic effects of CcfM on magnetosome chain organization and cell morphology are supported by the finding that CcfM interacts with the magnetoskeleton-related MamY and the actin-like MamK via distinct motifs, and with the cell shape-related cytoskeleton via MreB. We further demonstrate that CcfM promotes motility and magnetic alignment in structured environments, and thus likely confers a selective advantage in natural habitats of magnetotactic bacteria, such as aquatic sediments. Overall, we unravel the function of a prokaryotic cytoskeletal constituent that is widespread in magnetic and nonmagnetic spirilla-shaped Alphaproteobacteria.
趋磁细菌通过细胞内的磁性细胞器——磁小体，在地球磁场中运动，磁小体被排列成链状，并由专门的磁小体特异性细胞骨架（“磁骨架”）定位在细胞中部。然而，磁小体链的组织和由此产生的趋磁性与细胞形状之间的联系仍然难以捉摸。在这里，我们描述了细胞骨架决定因素 CcfM（诱导卷曲螺旋丝与磁骨架相互作用的卷曲螺旋丝），它将磁骨架与细胞形态调节联系起来。膜锚定的 CcfM 通过其卷曲螺旋基序沿细胞内正曲率区域呈丝状排列，并且不依赖于磁骨架。CcfM 的过表达导致额外的周向定位模式，与细胞曲率的急剧增加以及磁小体链的定位错误或完全破坏相关。相比之下，的缺失导致细胞曲率降低、细胞分裂受损以及较短、双磁小体链的主要形成。CcfM 对磁小体链组织和细胞形态的多效性影响得到了支持，因为发现 CcfM 通过不同的基序与磁骨架相关的 MamY 和肌动蛋白样 MamK 相互作用，并通过 MreB 与细胞形状相关的细胞骨架相互作用。我们进一步证明 CcfM 促进了在结构化环境中的运动和磁性对齐，因此在趋磁细菌的自然栖息地（如水生沉积物）中可能赋予了选择性优势。总的来说，我们揭示了一种在磁性和非磁性螺旋形 Alphaproteobacteria 中广泛存在的原核细胞骨架成分的功能。
