Snowflake yeast overcome diffusion limited nutrient acquisition by the generation of spontaneous flows

Snowflake yeast is a laboratory evolved multicellular organism, whose macroscopic size puts demands on its nutrient requirement, which cannot be met via diffusion alone, necessitating mixing of the local fluid environment. Typically, such mixing is achieved via appendages that mechanically stir the external fluid. While this requires the emergence of novelty and its subsequent fixation in early multicellular organisms, purely physical mechanisms such as emergent nutrient density gradients can also mix the local environment. Our work shows how fluid density driven instabilities, generated spontaneously via the organismal metabolic activity, can mitigate diffusion limitation in the nascent multicellular organism snowflake yeast allowing it to reach macroscopic sizes. Furthermore, we show how these flows help the organism achieve exponential growth up to macroscopic (millimetric) sizes.