The expression of phenotypic variability can enhance geometric mean fitness and act as a bet-hedging strategy in unpredictable environments . Metazoan bet hedging usually involves phenotypic diversification among an individual's offspring [2-6], such as differences in seed dormancy. Virtually all known microbial bet-hedging strategies, in contrast, rely on low-probability stochastic switching of a heritable phenotype by individual cells in a clonal group [7-10]. This is less effective at generating within-group diversity when group size is small. Here we describe a novel microbial bet-hedging behavior that resembles individual-level metazoan bet hedging. Sinorhizobium meliloti stores carbon and energy in poly-3-hydroxybutyrate (PHB) as a contingency against carbon scarcity . We show that, when starved, dividing S. meliloti bet hedge by forming two daughter cells with different phenotypes. These have high and low PHB levels and are suited to long- and short-term starvation, respectively. The low-PHB cells have greater competitiveness for resources, whereas the high-PHB cells can survive for over a year without food, perhaps until a legume host is next available.
Bibliographical noteFunding Information:
The authors thank Michael Travisano and Tony Dean for helpful discussions, Daniel Gage for providing GFP-labeled Sinorhizobium meliloti 1021 pDG71, Mitch Hoverman for laboratory assistance, and the University of Minnesota Imaging Center. This work was supported by National Science Foundation (NSF) grants DEB-0918897 and DEB-0808234 and an NSF predoctoral fellowship (W.C.R.).