In a groundbreaking study poised to reshape our understanding of bacterial motility, researchers have unveiled intricate structural and evolutionary details of the flagellar motor in Campylobacter jejuni, an important bacterial pathogen. The bacterial flagellum, a nanoscopic rotary engine, has long fascinated microbiologists for its elegant simplicity and efficiency—principally studied in organisms such as Escherichia coli and Salmonella enterica. However, these models represent only a fraction of bacterial diversity. Many bacteria, including C. jejuni, feature far more elaborate flagellar motors whose biochemical complexities and evolutionary origins have remained enigmatic—until now.
Leveraging a multidisciplinary approach that combines high-resolution cryo-electron microscopy with rigorous genetic, biochemical, and phylogenetic analyses, the study deciphers auxiliary structural components that endow C. jejuni’s motor with enhanced stability and torque-generation capacities. Central to their findings is the identification of a novel ‘E ring’ composed of 17 homodimers of the protein FlgY, which assembles circumferentially around the MS ring, a pivotal basal body structure. This E ring is not a mere architectural curiosity but appears critical for anchoring additional scaffolding proteins and stabilizing the entire rotary apparatus under the mechanical stresses of high-speed rotation.
In addition to the E ring, the researchers describe a sophisticated cage-like network involving proteins FcpM, FcpN, FcpO, and PflD. This cage forms an encompassing lattice around the motor’s stator complexes—energy transducing units responsible for torque generation. Intriguingly, these stator units are not randomly dispersed but preserved in a symmetric assembly coinciding with the unique 17-subunit E ring, suggesting a finely tuned coupling between these accessory components that maximizes motor efficiency and durability.
Bridging the E ring and the surrounding cage, the study highlights spoke–rim formations mediated by the interactions between PflA and PflB proteins. This structural spoke arrangement, mimicking a wheel’s spokes, strengthens the motor’s scaffolding network and further stabilizes the stator complexes. The extraordinary modularity and architectural complexity of these assemblies underscore evolutionary adaptations that likely confer enhanced motility advantages to C. jejuni in its ecological niches, where precise and powerful motility can mean the difference between colonization success and failure.
Moving beyond structural characterization, the team utilized phylogenetic methodologies to explore the evolutionary trajectory of these complex motor components. Their analyses reveal that the E ring and spoke structures are not anomalies but ancestral features with a surprisingly widespread distribution across diverse bacterial lineages. This suggests an ancient origin predating the divergence of multiple phyla—a finding that dramatically extends our understanding of flagellar motor evolution, beyond the oversimplified models based on enteric bacteria.
Moreover, the study uncovers compelling evidence for the evolutionary co-option of type IV pilus components into the flagellar motor machinery in the Campylobacterota phylum, to which C. jejuni belongs. This molecular repurposing event presumably equipped these bacteria with the elaborate scaffolds needed to support extraordinary torque and stability demands, highlighting an elegant example of evolutionary innovation through modular assembly and protein function reassignment.
The functional consequences of these complex motor architectures are profound. Compared to simpler bacterial motors, the C. jejuni motor can sustain higher torque output and rotational speeds, thereby enhancing its chemotactic abilities under diverse environmental challenges. These adaptive benefits possibly underpin the pathogenic success of C. jejuni, which relies on aggressive motility to traverse mucus layers and establish infection within host organisms.
From a structural biology perspective, the revelation of 17-fold symmetry in FlgY homodimer arrangements and their direct physical and functional linkages to other motor elements pushes the envelope in molecular microbial nanomachinery. It challenges previously held notions regarding the stoichiometric and spatial organization of flagellar motor complexes and invites re-examination of torque generation mechanisms under novel structural constraints.
The interdisciplinary strategy adopted in this investigation exemplifies how integrated structural, genetic, and computational tools can uncover hidden complexities in well-known biological machines. The synergy of advanced cryo-EM imaging with detailed protein interaction assays, coupled with evolutionary genomics, constructs a vivid narrative of both the assembly and the long evolutionary dance that sculpted the C. jejuni flagellar motor into its present form.
This study also raises intriguing questions about the dynamics and regulation of such complex flagellar systems. For example, how do the multiple interacting scaffolds assemble in vivo during flagellar biogenesis, and what molecular signals coordinate the integration of these auxiliary components with core motor elements? Understanding these processes could pave the way for the development of novel antibacterial strategies aimed at disrupting motility — a key factor in bacterial pathogenesis.
Beyond microbiology, these findings inspire biomimetic engineering pursuits. The sophisticated organization and interplay of modular scaffolds in flagellar motors embody principles of nanoscale mechanical design that could inform the creation of synthetic nanomachines or microrobots, offering revolutionary applications in medicine and technology.
This comprehensive structural elucidation of Campylobacter’s complex flagellar motor thus represents a paradigm shift, blending evolutionary biology with cutting-edge molecular insights while laying fertile ground for translational innovations. As the field progresses, further exploration of bacterial flagellar diversity promises to unlock even deeper understanding of microbial motility, adaptation, and evolution.
In conclusion, the work spearheaded by Feng, Tachiyama, He, and colleagues delivers an unprecedented window into the structural sophistication and evolutionary ingenuity of bacterial flagellar motors, especially within the enigmatic Campylobacterota lineage. By delineating the roles of novel scaffold components and their integration into highly symmetric molecular assemblies, the study enriches a classic model with fresh complexity and evolutionary perspective. It is a compelling reminder that the microscopic engines driving bacterial life remain a continual source of scientific wonder and technological inspiration.
Subject of Research: Structural, functional and evolutionary characterization of complex bacterial flagellar motors in Campylobacter jejuni.
Article Title: Structural insights into the assembly and evolution of a complex bacterial flagellar motor.
Article References:
Feng, X., Tachiyama, S., He, J. et al. Structural insights into the assembly and evolution of a complex bacterial flagellar motor. Nat Microbiol (2026). https://doi.org/10.1038/s41564-025-02248-5
Image Credits: AI Generated
