Evolution and stability of complex microbial communities driven by trade-offs.

Microbial communities are ubiquitous in nature and play an important role in ecology and human health. Cross-feeding is thought to be core to microbial communities, though it remains unclear precisely why it emerges. Why have multi-species microbial communities evolved in many contexts and what protects microbial consortia from invasion? Here, we review recent insights into the emergence and stability of coexistence in microbial communities.

Homeostasis of cytoplasmic crowding by cell wall fluidization and ribosomal counterions.

In bacteria, algae, fungi, and plant cells, the wall must expand in concert with cytoplasmic biomass production, otherwise cells would experience toxic molecular crowding or lyse. But how cells achieve expansion of this complex biomaterial in coordination with biosynthesis of macromolecules in the cytoplasm remains unexplained, although recent works have revealed that these processes are indeed coupled. Here, we report a striking increase of turgor pressure with growth rate in suggesting that the speed of cell wall expansion is controlled via turgor.

Plasticity of growth laws tunes resource allocation strategies in bacteria.

Bacteria like E. coli grow at vastly different rates on different substrates, however, the precise reason for this variability is poorly understood. Different growth rates have been attributed to 'nutrient quality', a key parameter in bacterial growth laws.

Membrane potential mediates the cellular response to mechanical pressure.

Mechanical forces have been shown to influence cellular decisions to grow, die, or differentiate, through largely mysterious mechanisms. Separately, changes in resting membrane potential have been observed in development, differentiation, regeneration, and cancer. We now demonstrate that membrane potential is the central mediator of cellular response to mechanical pressure.

Homeostasis of cytoplasmic crowding by cell wall fluidization and ribosomal counterions.

In bacteria, algae, fungi, and plant cells, the wall must expand in concert with cytoplasmic biomass production, otherwise cells would experience toxic molecular crowdingor lyse. But how cells achieve expansion of this complex biomaterial in coordination with biosynthesis of macromolecules in the cytoplasm remains unexplained, although recent works have revealed that these processes are indeed coupled. Here, we report a striking increase of turgor pressure with growth rate in , suggesting that the speed of cell wall expansion is controlled via turgor.

Coexisting ecotypes in long-term evolution emerged from interacting trade-offs.

Evolution of complex communities of coexisting microbes remains poorly understood. The long-term evolution experiment on Escherichia coli (LTEE) revealed the spontaneous emergence of stable coexistence of multiple ecotypes, which persisted for more than 14,000 generations of continuous evolution. Here, using a combination of experiments and computer simulations, we show that the emergence and persistence of this phenomenon can be explained by the combination of two interacting trade-offs, rooted in biochemical constraints: First, faster growth is enabled by higher fermentation and obligate acetate excretion.