Selection for novel metabolic capabilities inSalmonella enterica

Abstract

Bacteria are known to display extensive metabolic diversity and many studies have shown that they can use an extensive repertoire of small molecules as carbon‐ and energy sources. However, it is less clear to what extent a bacterium can expand its existing metabolic capabilities by acquiring mutations that, for example, rewire its metabolic pathways. To investigate this capability and potential for evolution of novel phenotypes, we sampled large populations of mutagenized Salmonella enterica to select very rare mutants that can grow on minimal media containing 124 low molecular weight compounds as sole carbon sources. We found mutants growing on 18 of these novel carbon sources, and identified the causal mutations that allowed growth for four of them. Mutations that relieve physiological constraints or increase expression of existing pathways were found to be important contributors to the novel phenotypes. For the remaining 14 novel phenotypes, whole genome sequencing of independent mutants and genetic analysis suggested that these novel metabolic phenotypes result from a combination of multiple mutations. This work, by virtue of identifying the genetic and mechanistic basis for new metabolic capabilities, sheds light on the properties of adaptive landscapes underlying the evolution of novel phenotypes.

Succinate utilisation by Salmonella is inhibited by multiple regulatory systems

“…Here, we devised an in vitro experimental strategy to search for novel regulatory mechanisms involved in the modulation of succinate utilisation under aerobic conditions. This type of experimental evolution has a successful track record [ 26 ] and has previously been used to generate Salmonella mutants that grow on novel carbon sources [ 27 ]. Our subsequent genetic dissection identified two novel RpoS-independent regulatory mechanisms that repress succinate utilisation via the CspC and IscR regulatory proteins.…”