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 Magnetospirillum gryphiswaldense. 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 ccfM 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，磁小体在地磁场内进行运动，这些细胞器排列成一条链并通过专用的磁小体特异性细胞骨架（“磁骨骼”）定位在中细胞处。然而，如何磁小体的链组织和由此产生的趋磁性与细胞的形状联系在一起仍然难以捉摸。在这里，我们描述了细胞骨架行列式CCFM（曲率诱导卷曲螺旋灯丝与所述magnetoskeleton交互），其magnetoskeleton链接到细胞形态调控磁螺gryphiswaldense。膜锚定的CcfM通过其螺旋线圈图案沿着内部正细胞曲率区域以丝状模式定位，并且与磁骨架无关。CcfM过表达会导致其他周向定位模式，与细胞曲率的急剧增加以及磁小体链的错误定位或完整的链断裂有关。相反，删除ccfM会导致细胞曲率降低，细胞分裂受损以及较短，双倍的磁小体链形成。CcfM通过独特的基序与磁骨架相关的MamY和肌动蛋白样的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，这一发现支持了CcfM对磁小体链组织和细胞形态的多效性效应。我们进一步证明，CcfM在结构化环境中促进运动性和磁对准，因此可能在趋磁细菌的自然栖息地（例如水生沉积物）中赋予选择优势。总的来说，我们揭示了在磁性和非磁性螺旋形Alphaproteobacteria中普遍存在的原核细胞骨架成分的功能。