A groundbreaking study led by the University of Auckland unveils the ancient evolutionary origins of bacterial motility—one of nature’s earliest molecular motors dating back nearly 4 billion years. This cutting-edge research, recently published in the prestigious journal mBio, deciphers the inception and structural diversification of the MotAB stator complex, a protein assembly essential for bacterial flagellar propulsion. By integrating deep computational modeling with empirical laboratory assays, scientists are now unraveling the intricate mechanics behind how primordial bacteria first mastered movement, a vital milestone in the evolution of life on Earth.
At the heart of this discovery lies the bacterial stator, a sophisticated protein complex embedded within the cell wall that functions analogously to pistons in an engine. These stators convert ionic flux—charged particles flowing across membranes—into mechanical torque, powering the rotation of the flagellum, a whip-like appendage propelling bacterial cells through fluid environments. Understanding how these motor proteins arose from simpler molecular ancestors sheds light on a pivotal chapter in molecular evolution, highlighting the innovation that transformed basic ion transport mechanisms into complex motility apparatuses.
Dr. Caroline Puente-Lelievre of the University of Auckland’s School of Biological Sciences emphasizes the significance of motion at biological scales, stating that molecular movement is fundamentally essential from the smallest microbes to the largest multicellular organisms. The team’s efforts focused on modeling the evolutionary trajectory of MotA and MotB proteins—the core components of the stator complex—using advanced structural biology techniques, including the revolutionary AlphaFold AI developed by DeepMind. This breakthrough algorithm enabled highly accurate predictions of three-dimensional protein folding, a task once daunting due to experimental constraints.
Bacteria’s ancient origins, dating to a time when Earth’s atmosphere was a cauldron of volcanic activity and hostile chemical conditions, framed the context for this evolutionary innovation. These single-celled organisms needed efficient mechanisms for locomotion to survive and exploit their harsh surroundings. The flagellar motor, powered by the stator complex, emerges as one of the earliest sophisticated biological machines, marking a significant evolutionary advancement. Unlike inert molecular structures, these protein motors demonstrate remarkable efficiency and durability, minimally altered across billions of years.
The study’s multidisciplinary approach combined genomic analysis of over 200 bacterial species, complex computational phylogenetic trees, and refined 3D protein structure comparisons. This comprehensive dataset illuminated how stators evolved from simpler ancestral ion transport proteins, which initially served more rudimentary functions than generating mechanical force. Dr. Nick Matzke, senior researcher, draws parallels with macroevolutionary innovations like feather development in dinosaurs, postulating similar evolutionary co-option where existing molecular tools were repurposed to serve novel biological functions, including cellular motility.
Detailed structural comparisons revealed the torque-generating domains responsible for converting ion flow into rotational energy. These domains are conserved among diverse bacterial stator proteins, illustrating the evolutionary pressure to maintain efficient energy transduction mechanisms across species. To validate these structural predictions, the research team conducted elegant functional assays with genetically engineered Escherichia coli strains missing critical stator interfaces. The inability of these mutants to swim conclusively demonstrated that specific protein regions are indispensable for motility, bridging computational models with biological functionality.
The implications of this research extend beyond simply understanding bacterial motion. By reconstructing ancestral protein sequences and predicting their three-dimensional forms, scientists gain valuable insights into how complex molecular machines evolve from simpler components. This process of molecular bricolage—where nature retools existing protein frameworks for new functions—demonstrates a fundamental principle of evolutionary biology: complexity emerges not purely from de novo invention but through modification and redeployment of pre-existing structures.
Advances in structural biology, fueled by artificial intelligence and computational power, are revolutionizing the study of molecular evolution. The AlphaFold system enables nearly instantaneous modeling of previously uncharacterized proteins, dramatically accelerating our ability to hypothesize functional mechanisms at the atomic level. For microbiologists and biophysicists, these tools unlock new potential to explore the molecular underpinnings of life’s earliest innovations, from motility to metabolic pathways.
“We’re living in an era where the vast genetic diversity of microbial life is being uncovered daily,” notes Assistant Professor Matthew Baker from UNSW Sydney. “Our study harnessed this wealth of genomic data to cast a wide evolutionary net, identifying stator-like proteins across distant bacterial lineages and exploring how their structures inform us about the origins and evolution of these molecular motors.” Such comparative analyses reveal both conserved elements essential for function and lineage-specific adaptations reflecting diverse ecological niches.
Beyond academic curiosity, understanding bacterial flagella and their motors has practical applications. These microscopic engines inspire biomimetic designs in nanotechnology and synthetic biology, where engineers seek to replicate efficient molecular motions for innovations in drug delivery, microscale robotics, and environmental sensing. By decoding the evolutionary history and structural diversity of these natural motors, scientists can better harness biology’s design principles for technological advancement.
Funded by prominent organizations including the Human Frontier Science Program, the University of Auckland Faculty of Science, the John Templeton Foundation, and the Alfred P. Sloan Foundation, this work epitomizes the power of international collaboration and interdisciplinary research. Co-authors such as Pietro Ridone, Dr. Jordan Douglas, Kaustubh Amritkar, and Assistant Professor Betül Kaçar contributed vital expertise spanning genomics, biophysics, and evolutionary biology. Together, their insights illuminate a molecular narrative dating back billions of years, shedding light on how early life forms achieved the dynamic capabilities essential for survival and diversification.
Ultimately, this research not only deepens our understanding of bacterial motility but invites reflection on the molecular ingenuity underpinning all life. Evolution’s creative repurposing of simple ion transport proteins into sophisticated molecular motors reveals nature’s capacity for engineering complex biological systems in response to environmental challenges. As we continue to decode the structures and functions of ancient protein machinery, we unravel the foundational steps through which life first mastered movement—an enduring story written in the language of molecules.
Subject of Research: Cells
Article Title: Evolution and structural diversity of the MotAB stator: insights into the origins of bacterial flagellar motility
News Publication Date: 10-Sep-2025
Web References: DOI: 10.1128/mbio.03824-24
Image Credits: Caroline Puente-Lelievre
Keywords: bacterial motility, MotAB stator, flagellar motor, protein evolution, molecular motors, AlphaFold, structural biology, ion transport proteins, bacterial evolution, molecular dynamics, ancestral protein reconstruction, computational modeling
