Microbial cooperation at high temperatures

Abstract

Microorganisms can cooperate with each other, meaning that individual cells work together to pursue a common interest. Cooperation can be crucial for microorganisms to survive stressful environmental conditions. In this work, we report on the cooperative behaviour by the yeast S. cerevisiae and the bacterium E. coli, which stimulates survival and growth at high temperatures. Our lab had already discovered that genetically identical yeast cells cooperate with each other via the secretion of a public good (the antioxidant glutathione), to extend habitability of high temperatures. However, microbes naturally live in communities, where they coexist with other strains and species. These microbial communities are crucial to the health of an ecosystem, but their habitats are warming up due to climate change. So, understanding their response to a rising temperature may be crucial to keep ecosystems healthy. We take it one step further and study the cooperation between different yeast strains at high temperatures. We found that not only a population of genetically identical cells, but also different strains cooperate with each other, to collectively survive under high temperature conditions. We performed so-called co-existence experiments at high temperatures, where we combined two different yeast strains, one genetically fitter than the other. Depending on the initial composition of the mixed population, we obtained two outcomes. In the first outcome, the genetically fitter strain helps the less fit strain to grow. In the second outcome, vice versa, the less fit strain helps the fitter strain to grow. A mathematical model that reproduces the experimental data, predicts an additional outcome, where both strains would help each other to grow. Additionally, we discovered a novel cooperative behaviour at high temperatures in the bacterium E. coli. We found that E. coli cells show similar growth behaviour compared to yeast and we hypothesize that a comparable cooperative behaviour lies at the basis, also regulated by the secretion of a public good. These results suggest that cooperation at high temperatures could be conserved amongst different microbial species.