Dynamics of Escherichia coli propagation, biofilm formation, and evolution

When bacteria, such as Escherichia coli, are inoculated into a soft agar plate they generate a steadily propagating front, exhibiting dynamics similar to what has been observed for other propagating fronts, such as a propagating flame front. We determined that propagating fronts of Escherichia coli can be described using a reaction-diffusion model analogous to propagating flame fronts. During the course of the experiments different types of pattern formation were observed, one in particular was determined to be the result of Lewis number instabilities.;Motile Escherichia coli are capable of forming biofilms, which are surface attached communities of bacteria. Biofilms are found ubiquitously in nature and are capable of long-term survival. Little is known about the dynamics of cellular growth, death, and evolution within bacterial biofilms. By aging Escherichia coli biofilms in the laboratory, we determined that cells harvested from 22-day-old biofilms express a competitive advantage over cells incubated in biofilms for shorter periods of time. Whereas the older and younger populations of biofilm harvested cells exhibit similar abilities to form biofilms in the absence of competition or in competition for a fresh surface, the 22-day-old biofilm harvested cells demonstrate a clear advantage over 1-day-old biofilm harvested cells when competing in the presence of a pre-existing biofilm. This phenomenon is similar to the growth advantage in stationary phase, or GASP, phenotype previously demonstrated for planktonically grown cells.;To better understand how the 22-day-old biofilm harvested cells are manifesting their advantage over 1-day-old biofilm harvested cells, a fluorescent protein expression system was created to monitor biofilm development in situ. Two different-coloured fluorescent protein expressing strains were aged in a biofilm for 1 or 22 days, harvested and used in a variety of assays that were monitored using confocal laser scanning microscopy. The most striking result of the image analysis is that the 22-day-old biofilm harvested cells form clumps in defined regions of the existing biofilm whereas the 1-day-old biofilms harvested cells do not form clumps. We have concluded that the clump formation by the 22-day-old biofilm harvested cells is due to clonal growth, indicating an increased proliferation ability of the 22-day-old population.