A model for generating several adaptive phenotypes from a single genetic event

Abstract

Microbial populations adapt to environmental fluctuations through random switching of fitness-related traits in individual cells. This increases the likelihood that a subpopulation will be adaptive in a future milieu. However, populations are particularly challenged when several environment factors change simultaneously. We suggest that a populationcan rapidly adapt to multiple environmental changes if individual members stochastically flip a hub-switch that controls a set of adaptive phenotypes in a single event. This mechanism of coupling phenotypic outcomes via a hub-switch can protect a population against large fluctuations in size. Here we report that the general amino acid transporter Gap1 isa potential hub-switch. The GAP1 gene is flanked by two direct repeats that can lead to GAP1 deletions (δgap1) and a self-replicating GAP1 circle. Thus, an isogenic GAP1 population can differentiate into two variant, reversible genotypes, δgap1 or GAP1circle. These subpopulations have different phenotypic advantages. A δgap1 population has a selective advantage on allantoin or ammonium as a nitrogen source and high stress tolerance. Advantages of the GAP1 population include amino acid uptake, fast energy recruitment by trehalosemobilization, and in some cases, adherent biofilm growth. Our proposed model of a hub-switch locus enhances the bet-hedging model of population dynamics. © 2013 Landes Bioscience.