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.

Metal nanoparticles have promising potential for use in medical applications, such as imaging or targeted drug delivery. Current methods of production of nanoparticles are expensive and make use of harsh reagents. Because of these limitations, nanoparticles are not yet widely available, limiting the use in medical applications. To commercialize nanoparticle production, it is necessary to develop a nanoparticle synthesis process that is cheap, safe and environmentally friendly. Earlier research has shown that biosynthesis of nanoparticles is possible in many different organisms using certain reducing peptide sequences. Biosynthesis of metallic nanoparticles is cheaper, safer and occurs under physiological conditions, making it an ideal process for the up scaling of nanoparticle production. However, shape and size of the nanoparticle are hard to control and yields are low when biosynthesis is used, limiting the use of biosynthesis. To overcome the problem of shape and size control, it is proposed to use viral capsids as protein cages to restrict the size of synthesized nanoparticles to the inside of the capsid. To implement this, metal ion reducing peptides were fused to the monomers of self-assembling capsids in a way that they were displayed on the inside of the capsid. It was shown that with the adjusted monomers, the capsids still self-assemble. Nanoparticle formation was attempted, but results were inconclusive.