  Metagenomics has revealed hundreds of bacterial species in almost all
microbiota. In a few well-studied cases, bacterial communities have been
observed to coordinate their metabolic fluxes. In principle, bacteria can
divide tasks to reap the benefits of specialization, as in human economies.
However, the benefits and stability of an economy of bacterial specialists are
far from obvious. Here, we physically model the population dynamics of bacteria
that compete for steadily supplied resources. Importantly, we explicitly model
the metabolic fluxes yielding cellular biomass production under the constraint
of a limited enzyme budget. In our framework, we find that population dynamics
generally leads to the coexistence of different metabolic types, which satisfy
an extended competitive exclusion principle (even allowing for adaptive
mutation). We establish that these consortia act as cartels, whereby population
dynamics pins down resource concentrations at values for which no other
strategy can invade. Finally, we propose that at steady supply, cartels of
competing strategies automatically yield maximum biomass, thereby achieving a
collective optimum.
