Characterization of myxobacterial A-motility: insights from microcinematographic observations.

Myxococcus xanthus, a predatory soil bacterium, has long been used as a model organism to study bacterial gliding motility. Research has revealed that two fundamentally distinct motor systems power gliding in this bacterium: repeated extensions and retractions of pili mediate social or (S-) motility, whereas the motor powering adventurous or (A-) motility has not yet been identified with certainty. Several different hypotheses to explain A-motility have been suggested and differ with respect to the involved motor structures as well as the mechanics of motility. As some of the more recent models invoke helically arranged structures and processes that require rotations of the cell, we decided to re-examine myxobacterial motility using microcinematographic techniques. This re-examination was also prompted by the lack of direct experimental data on the rotation of M. xanthus during gliding. Microcinematographic observations of deformed cells and cells containing large stationary intracellular structures reveal clearly that M. xanthus gliding does not require cell rotation.