Natural Size Variation Amongst Protocells Leads to Survival and Growth Under Hypoosmotic Conditions

Membrane growth is vital to the evolution of cellular life. For model protocells, this is typically achieved through competition between different protocell populations or by adding extra amphiphiles. This work demonstrates an alternative mechanism for protocell membrane growth: hypoosmotic shocks, which could have occurred naturally in the protocell environment, leading to the redistribution of lipids within a single population of vesicles. Here we report that, even without an additional lipid supply, nanoscale and giant fatty acid vesicles can withstand substantial osmotic pressures through membrane growth, whilst also retaining a significant portion of their contents. This stands in contrast to phospholipid systems, which burst and release their contents under the same conditions. Notably, the fatty acid giant vesicles retained contents following hypoosmotic shocks ten times higher than the predicted tolerance levels. The observed robustness is likely enabled by the membrane's incorporation of additional amphiphiles from smaller and less tense vesicles within the same population. The dynamic nature of these fatty acid-based model protocells not only supports membrane growth but also enables protocell survival in hypoosmotic environments.