Competition for space in growing bacterial populations: what determines the winners and losers?

In the natural environment, bacterial populations often form densely packed self-assembled structures in cavities or on surfaces. Understanding how cells compete for space in these communities is essential if we are to translate our understanding of population dynamics and evolution in well-mixed communities to these real-life situations. We have used fluorescence microscopy to study the competition for space between thousands of bacterial cells as they colonize a two-dimensional agarose surface. For each individual progenitor cell, we quantify the likelihood that their descendants will out-perform their neighbours for local space under a range of environmental conditions, and how this affects the patterns of genetic segregation within the resulting surface community. Our results show that the local stress distributions which arise when two microcolonies push against each other play an important role in distinguishing “winners” from “losers” – but that individual cell lag times on the surface are also a critical factor.