Body-wrapping anterior flagella drive ultrafast swimming in bacterial zoospores
Most bacteria swim at [~]10 body lengths per second (bl s-1), yet some microorganisms move far faster, and the physical design principles enabling such extreme motility remain poorly understood. Here we uncover an ultrafast swimming strategy in Actinoplanes missouriensis zoospores, which reach up to 560 m s-1 ([~]500 bl s-1), the fastest relative swimmer reported for any microorganism. High-speed imaging shows that propulsion is driven by an anterior, body-wrapping bundle of short flagella that rotate synchronously as a right-handed helix at [~]150 Hz. This architecture generates high thrust without extreme motor speeds and contrasts with the canonical rear-bundle paradigm of bacterial swimming. Microfluidic assays further demonstrate that this propulsion mode enhances dispersal across the flow interface, providing a mechanism for rapid colonization during the transient motile phase of the life cycle. Furthermore, chemotaxis-dependent reorientation is observed, suggesting that zoospore swimming can be directionally regulated. These results identify a new locomotion principle in which supramolecular organization of multiple flagella, rather than motor speed alone, sets the upper limits of bacterial swimming and offers inspiration for the design of high-performance microswimmers.