The role of motility in species coexistence

What makes ecosystems stable or fragile? What prevents one species from outcompeting all others, and hence drive them to extinction? These questions have captivated biologists since Darwin, and it is increasingly recognized that understanding the mechanisms that stabilize or destabilize species coexistence is of fundamental importance for studies of biodiversity, not only at the macroscale (environmental / conservation research), but also at the microscale (medical / microbiome research).

We developed a novel laboratory experiment that allows investigation of microbial population dynamics in a spatially extended habitat, and discovered a new mechanism for coexistence of bacterial species¹. The project has been wonderful collaboration, leveraging our group’s expertise in bacterial motlity, and AMOLF colleague Sander Tans’ group’s expertiese in bacterial growth.

Fig. 1. Cartoon of experiment showing coexistence between bacteria (red and blue) that cyclically colonize nutrient patches (green).

Our new experiment simulates within a petri dish the widely observed ecological phenomenon of cyclic colonization of nutrient patches under repeated environmental disturbances (Fig. 1). Fluorescence imaging allowed us to quantify the bacterial population dynamics in both time and space. By combining experiments in both natural isolate bacteria from the wild, and engineered laboratory strains, we discovered that a trade-off between growth and motility leads to the spontaneous emergence of spatial niches that allow bacterial strains to coexist.

Fig. 2. (Left) Fluorescence microscopy of bacterial populations across the gel after the competition. (Right) Bacterial strains A and B were shown to both outcompete the other when rare, and hence coexist..

References

1. Gude, S., Pinçe, E., Taute, K.M., Seinen, A.B., Shimizu, T.S.* and Tans, S.J.* (2020). Bacterial coexistence driven by motility and spatial competition. Nature 578, 588-592. (*Joint correspondence)