4 | DISCUSSION
Bacteria have adapted strategies to translocate themselves in solid as
well as liquid mediums. In a liquid medium while growth and movement are
more of an individual style; but in a colony, the cells translocate as
different groups. In this study, we have distinctly demonstrated that
while the peripheral cells in a grown-up colony are exhibiting more
twitching motility, cells towards the centre of the colony are
exhibiting less twitching motility. This heterogeneity and
non-uniformity within a colony are prominently observed and presented in
this study in the form of twitching motility in R. solanacearum .
It indicates that within a bacterial colony there exist different
niches. The bordering cells joining to make a continuous ring-like
structure in the spotted area behave in a synchronized fashion during
the twitching motility. The behavior of cells in that region needs
further investigation regarding intercellular communication and their
synchronization process. There are studies related to different mutation
rates within a bacterial colony between peripheral and central cells
because the cells in the former region are considered active in cell
division whereas the cells in the latter region are considered
non-dividing (Reddy et. al 1997).
Not all bacteria in nature exhibit twitching motility. Twitching
motility has been mainly associated with biofilm formation. In R.
solanacearum colony, the bacteria form films one above the other, which
indicates the large number of bacteria that can be accommodated in a
given surface area. This is not observed in Escherichia coliwhere twitching motility is absent. A careful observation of
microcolonies in different dilutions suggests that microcolonies in a
more concentrated culture are more asymmetric than microcolonies in a
lower concentrated culture. This happens 16-18 h after spotting the
bacterial suspension. This raises an interesting question regarding the
sensing of microcolonies to each other and accordingly managing cell
division and translocation. A future study on this aspect is likely to
reveal interesting aspects of bacterial behavior in the bacterial
colony.
Our study on twitching motility dynamics in R. solanacearumcolony leads to an interesting future perspective to analyze the same in
other bacterial colonies such as Pseudomonas aeruginosa,
Myxococcus xanthus and Neisseria gonorrhoeae . Exactly the advantage
twitching motility provides to the pathogen within a host will be an
interesting study in future.