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.