Mechanical Effects on the Ecology of Bacteria within Microchannels

Bacteria constantly compete for space and resources with other microbes. This has led them to evolve an array of active strategies, such as quorum sensing or excreting bacterial toxins, to outcompete their neighbors. One often overlooked feature that is essential to the dynamics of this competition, especially within confined microenvironments, is mechanical effects because cells regularly push and bump into their neighbors. We have been studying the spatial population dynamics of a model microbial community composed of two distinct populations of E. coli bacteria. These mixed populations are cultured within open-ended monolayer microchambers, which can support the continuous growth of the cells for extended periods of time, and imaged for up to 24 hrs by time-lapse microscopy. Competition between the two species often results in one species completely eradicating the other, which we refer to as “fixation”. However, due to their pill shaped geometry, the two populations tend to jam into an organized structure, much like the nematic phase of liquid crystals. This can enable the cells to “coexist” for extended periods of time despite signficant differences in growth rate. By altering the cell morphology through modification of the actin homolog MreB, in E. coli, we can study the effects of cell shape on the fixation vs. coexistence dynamics. These findings are recapitulated by simulations and qualitatively reproduced by a statistical model, laying a foundation for elucidating the principles of community assembly in dense confined populations.