Metabolically-driven flows enable exponential growth in macroscopic multicellular yeast

Area of Science:

• Evolutionary biology
• Biophysics
• Cell biology

Background:

• Multicellularity offers evolutionary advantages, often linked to increased organism size.
• Large size in multicellular organisms presents challenges in nutrient transport, typically solved by specialized systems.
• Unicellular organisms face diffusion limitations as size increases.

Purpose of the Study:

• To investigate if emergent biophysical mechanisms can facilitate nutrient transport in nascent multicellular clusters.
• To determine if metabolic activity can drive fluid flows supporting growth in yeast clusters.
• To explore the role of physical processes as a scaffold for multicellular evolution.

Main Methods:

• Experimentally evolved snowflake yeast clusters were studied.
• Metabolic activity and density gradients were analyzed for their role in fluid flow generation.
• Nutrient transport rates and growth dynamics were measured in yeast clusters of varying sizes.
• Observed flow speeds were compared to those generated by cilia in multicellular organisms.

Main Results:

• Spontaneous fluid flows, driven by metabolically-generated density gradients, were observed in yeast clusters.
• These flows effectively transported nutrients throughout the clusters, overcoming diffusion limitations.
• Exponential growth was supported at macroscopic sizes previously thought to be limited by diffusion.
• Flow speeds achieved were comparable to those generated by cilia in extant multicellular organisms.

Conclusions:

• Emergent biophysical mechanisms, like metabolically driven fluid flows, can act as a 'biophysical scaffold' for multicellular evolution.
• These physical processes enable growth at larger sizes, preceding the development of genetically encoded transport systems.
• The co-option of conserved physical processes is a significant, yet often overlooked, factor in evolutionary innovation across biological scales.