Bacterial persistence and bet hedging in Sinorhizobium meliloti

We recently described a novel bethedging mechanism in which the bacterium Sinorhizobium meliloti responds to starvation by forming two discrete cell types via cell division. The old-pole daughter cell retains most of the resource, polyhydroxybutyrate (PHB) and is capable of surviving long-term starvation, while the low-PHB, new-pole daughter cell is capable of quickly resuming growth when starvation ends. Here we present additional data showing that the high-PHB, old-pole cells are similar to bacterial persisters, characterized by metabolic dormancy and antibiotic tolerance. Using two independent methods, we generated clonal populations of S. meliloti that varied in the frequency of the high- and low-PHB phenotypes, and then challenged these populations with ampicillin. Populations containing more high-PHB cells were significantly more antibiotic-tolerant. In a separate experiment, we used GFP fluorescence as a marker of overall metabolic activity. After 24 hours of starvation, new-pole cells were 64% brighter than their old-pole sister cells, demonstrating that the divergence in metabolic rate is rapid.