MICROBIAL EVOLUTION IN A SIMPLE UNSTRUCTURED ENVIRONMENT - GENETIC DIFFERENTIATION IN ESCHERICHIA-COLI

Populations of Escherichia coli initiated with a single clone and main tained for long periods in glucose-limited continuous culture, become polymorphic. In one population, three clones were isolated and by mean s of reconstruction experiments were shown to be maintained in stable polymorphism, although they exhibited substantial differences in maxim um specific growth rates and in glucose uptake kinetics. Analysis of t hese three clones revealed that their stable coexistence could be expl ained by differential patterns of the secretion and uptake of two alte rnative metabolites acetate and glycerol. Regulatory (constitutive and null) mutations in acetyl-coenzyme A synthetase accounted for differe nt patterns of acetate secretion and uptake seen. Altered patterns in glycerol uptake are most likely explained by mutations which result in quantitative differences in the induction of the glycerol regulon and /or structural changes in glycerol kinase that reduce allosteric inhib ition by effector molecules associated with glycolysis. The evolution of resource partitioning, and consequent polymorphisms which arise may illustrate incipient processes of speciation in asexual organisms.