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 has most commonly been shown to occur through competition between different protocell populations or with the addition of extra amphiphiles. We find an alternative mechanism for protocell membrane growth that occurs as a consequence of hypoosmotic shocks that could have occurred naturally in the protocell environment. We show that nanoscale and giant fatty acid vesicles can withstand substantial osmotic pressures through membrane growth, whilst also retaining a significant portion of their contents. Notably, the giant vesicles retained contents following osmotic shocks ten times higher than that predicted to be tolerable. This is likely enabled by the membrane’s incorporation of additional amphiphiles from less tense vesicles. The dynamic nature of these fatty acid-based model protocells provides a mechanism through which not only membrane growth occurs, but a mechanism which enables protocell survival in hypoosmotic environments.