Tracking how bacteria compete for space

We have tracked how bacteria compete for space when they grow on a surface, using a microscope and computer simulations. The "winners" of this ecological competition depend on both the speed at which bacteria colonize the space around them and the interactions between competing populations when they collide.

HFSP Young Investigator Grant holder Rosalind Allen and colleagues
authored on Mon, 23 November 2015

Competition for space is a very important concept in ecology, but investigating how animals or plants compete for space is laborious and time-consuming. Bacteria also compete for space when they grow on surfaces, and they are much easier to track in the laboratory. We have tracked how Escherichia coli bacteria compete for space when they grow on a flat surface. Using a microscope, we follow individual bacteria growing, distinguishing them using fluorescent labels. We also carry out computer simulations to match our experimental results. From our data, we identify bacteria which are “winners” of the ecological competition, in that they manage to occupy more space than that which immediately surrounds them. We also find “losers” whose expansion is thwarted by competition with surrounding populations. 

Figure: This shows a microscopy image of a surface that has been colonized by Escherichia coli bacteria in two different fluorescent colours (here shown red and green). By studying the statistics of the red patches we can investigate the ecological processes that influence competition for space in these experiments.

By analyzing our data, we can find out what features of individual bacteria make them winners or losers. We find that it matters how fast individual bacteria start to grow when they first colonise the surface; fast growers tend to be winners. We also find, however, that competition between colliding populations of bacteria at their boundaries also plays a role. This work shows how bacterial model systems can be used to shed light on ecological mechanisms that would be difficult or impossible to track for animals or plants, because they can be easily and rapidly grown and tracked in the laboratory.

Our HFSP grant is about how the initial arrangement in space of a bacterial population affects how it ultimately organizes itself as it grows in 3 dimensions into a surface-associated biofilm. This work, which was partially supported by the HFSP grant, complements this theme since it investigates the slightly simpler question of how bacteria organise themselves in 2 dimensions, on a flat surface. The process of spreading on a surface which is investigated in this paper can be viewed as a first stage in the 3D surface colonization that constitutes biofilm growth.

Reference

Competition for space during bacterial colonization of a surface. D. P. Lloyd and R. J. Allen, J. R. Soc. Interface 2015 12 20150608.

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