Abstract
BackgroundBacterial habitats, such as soil and the gut, are structured at the micrometer scale. Important aspects of microbial life in such spatial ecosystems are migration and colonization. Here we explore the colonization of a structured ecosystem by two neutrally labeled strains of Escherichia coli. Using time-lapse microscopy we studied the colonization of one-dimensional arrays of habitat patches linked by connectors, which were invaded by the two E. coli strains from opposite sides.ResultsThe two strains colonize a habitat from opposite sides by a series of traveling waves followed by an expansion front. When population waves collide, they branch into a continuing traveling wave, a reflected wave and a stationary population. When the two strains invade the landscape from opposite sides, they remain segregated in space and often one population will displace the other from most of the habitat. However, when the strains are co-cultured before entering the habitats, they colonize the habitat together and do not separate spatially. Using physically separated, but diffusionally coupled, habitats we show that colonization waves and expansion fronts interact trough diffusible molecules, and not by direct competition for space. Furthermore, we found that colonization outcome is influenced by a culture’s history, as the culture with the longest doubling time in bulk conditions tends to take over the largest fraction of the habitat. Finally, we observed that population distributions in parallel habitats located on the same device and inoculated with cells from the same overnight culture are significantly more similar to each other than to patterns in identical habitats located on different devices inoculated with cells from different overnight cultures, even tough all cultures were started from the same −80°C frozen stock.ConclusionsWe found that the colonization of spatially structure habitats by two interacting populations can lead to the formation of complex, but reproducible, spatiotemporal patterns. Furthermore, we showed that chemical interactions between two populations cause them to remain spatially segregated while they compete for habitat space. Finally, we observed that growth properties in bulk conditions correlate with the outcome of habitat colonization. Together, our data show the crucial roles of chemical interactions between populations and a culture’s history in determining the outcome of habitat colonization.
Highlights
Bacterial habitats, such as soil and the gut, are structured at the micrometer scale
Adler showed that Escherichia coli can spread on agar plates as traveling population waves [2,6]
We found that cells colonize a habitat from opposite sides by a series of traveling waves followed by an expansion front
Summary
Bacterial habitats, such as soil and the gut, are structured at the micrometer scale. Bacteria growing together in a common location actively change their surroundings by depleting nutrients, producing metabolites, and secreting signaling-molecules [2,6,7]. This collective conditioning of the environment, combined with the individual response of cells to their changing environment, can lead to the formation of complex patterns in spatiotemporal cell distributions [7,8]. Migration and colonization are important features of population dynamics. In his classic work, Adler showed that Escherichia coli can spread on agar plates as traveling population waves [2,6]. Despite the fact that such colony development is influenced by a myriad of environmental factors, regularities in these patterns have been described [16,17,18,19]
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