The Microbes They are a-Changin’

Generally, bacteria are not found as free-swimmers in nature. Instead, they have a tendency of forming dense communities clumped up on surfaces. Most of our knowledge of bacteria originates from cultures that have been grown in a liquid medium. This neglects the effect the space and structure of a surface can have on bacterial communities. In this study, researchers observed the effect that spatial structure can have on Pseudomonas aeruginosa. Three independent lineages of P. aeruginosa were allowed to disperse in separate plates. They were then flushed off their plates and a 1/1500 fraction of each original colony was inoculated at the center of a new plate. After several repetitions, the morphology of each colony began to change as their ability to disperse in a new plate improved.  A closer look at the cells from each lineage revealed that P. aeruginosa had evolved from having one flagellum to having 2-4 flagella. A genetic study on P. aeruginosa concluded that this was due to a point mutation in the fleN gene that occurred on all three lineages. Not only does this study present a prime example of convergent evolution, but it also offers a new perspective on the study of pathogens and infectious diseases. 

Figure from Ditmarsch et al. (2013). Image A displays the change in colony morphology of three independent lineages throughout 9 repetitions of the experiment. Image B shows a close up of the ancestral colony and the colonies at the end of the procedure.

Original article: Ditmarsch D., Boyle K.E., Sakhtah H., Oyler J.E., Nadell C.D., Deziel E., Dietrich L.E.P., & Xavier J.B. (2013). Convergent Evolution of Hyperswarming Leads to Impaired Biofilm Formation in Pathogenic Bacteria. Cell Reports 4(4): 697-708.