Inducing Novel Endosymbioses by Bacterial Implantation into Fungi

Microbial endosymbioses have had a profound impact on the evolution of life. The endosymbiosis- mediated acquisition of aerobic respiration and photosynthesis, resulting in mitochondria and chloroplasts, respectively, are prominent examples. However, understanding the requirements and mechanisms for endosymbiogenesis is challenging. By combining atomic force microscopy, optical microscopy, and nanofluidics, we developed a FluidFM-based method that allows to transplant bacteria directly into living cells. FluidFM-based injections of bacteria into R. microsporus, followed by FACS-mediated positive selection, allowed to introduce endosymbionts into this novel fungal host. We showed that the transplanted bacterium can be vertically transmitted across host generations and can be selected for. Adaptive laboratory evolution mitigated initially observed compromised host fitness and stabilized the endosymbiosis. Genetic and transcriptomic analyses shed light on the dynamics and fitness constraints during early endosymbiogenesis. Overall, our findings could improve the understanding of the balance between mutualism and antagonism in early endosymbiogenesis and help to study cost-benefit trade-offs