Tunable simultaneous propulsion by two distinct motility motors drives surface motility in bacteria

Motility enables cells to adapt to environmental cues, explore surfaces, and coordinate collective behaviors. Many organisms encode multiple motility systems, but whether these act independently or can operate together within the same cell has remained unclear. The predatory bacterium Myxococcus xanthus has long been thought to segregate its two propulsion systems: focal adhesions for gliding (A-motility) and type IV pili for twitching (S-motility), with each acting in distinct contexts. Here we overturn this view by providing the first direct demonstration that both systems are co-deployed and active within individual cells. Using dual-color high-resolution imaging, quantitative single-cell tracking, and agent-based simulations, we show that calcium, a key regulator of pili activity, tunes their relative engagement, shifting cells from adhesion- to pili-dominated propulsion with intermediate states combining both. This dynamic co-propulsion allows wild-type cells to move faster and explore more effectively than single-motility mutants, revealing a synergistic mode of motility integration shaped by environmental context.