ABSTRACT
Ralstonia solanacearum is a rod-shaped phytopathogenic bacterium
that causes lethal wilt disease in many plants. On solid agar growth
medium, in the early hour of the growth of the bacterial colony, the
type IV pili-mediated twitching motility, which is important for its
virulence and biofilm formation, is prominently observed under the
microscope. In this study, we have done a detailed observation of
twitching motility in R. solanacearum colony. In the beginning,
twitching motility in microcolonies was observed as a density-dependent
phenomenon that influences the shape and sizes of the microcolonies. No
such phenomenon was observed in Escherichia coli , where twitching
motility is absent. In the early phase of colony growth, twitching
motility exhibited by the cells at the peripheral region of the colony
was more prominent than the cells towards the centre of the colony.
Using a time scale photography and merging those into a video, twitching
motility was observed as an intermittent phenomenon that progresses in
layers in all directions as finger-like projections at the peripheral
region of a bacterial colony. Each layer of bacteria twitches on top of
the other and produces a multi-layered film-like appearance. We found
that the duration between the emergence of each layer diminishes
progressively as the colony becomes older. This study on twitching
motility demonstrates distinctly heterogeneity among the cells within a
colony regarding their dynamics and the influence of microcolonies on
each other regarding colony shape and size.