Swimming behavior of the monotrichous bacterium Pseudomonas fluorescens SBW25.

Motility is an important trait for some bacteria living in nature and the analyses of it can provide important information on bacterial ecology. While the swimming behavior of peritrichous bacteria such as Escherichia coli has been extensively studied, the monotrichous bacteria such as the soil inhabiting and plant growth promoting bacterium Pseudmonas fluorescens is not very well characterized. Unlike E. coli that is propelled by a left-handed flagella bundle, P. fluorescens SBW25 swims several times faster by rotating a right-handed flagellum. Its swimming pattern is the most sophisticated known so far: it swims forward (run) and backward (backup); it can swiftly 'turn' the run directions or 'reorient' at run-backup transitions; it can 'flip' the cell body continuously or 'hover' in the milieu without translocation. The bacteria swam in circles near flat surfaces with reduced velocity and increased turn frequency. The viscous drag load due to wall effect potentially accounts for the circular motion and velocity change, but not the turn frequency. The flagellation and swimming behavior of P. fluorescens SBW25 show some similarity to Caulobacter, a fresh-water inhabitant, while the complex swimming pattern might be an adaptation to the geometrically restricted rhizo- and phyllospheres.