A spore quality-quantity tradeoff favors diverse sporulation strategies in Bacillus subtilis

Quality-quantity tradeoffs govern the production of propagules across taxa and can explain variability in life-history traits in higher organisms. A quality-quantity tradeoff was recently discovered in spore forming bacteria, but whether it impacts fitness is unclear. Here we show both theoretically and experimentally that the nutrient supply during spore revival determines the fitness advantage associated with different sporulation behaviors in Bacillus subtilis. By tuning sporulation rates we generate spore-yield and spore-quality strategists that compete with each other in a microscopic life-cycle assay. The quality (yield) strategist is favored when spore revival is triggered by poor (rich) nutrients. We also show that natural isolates from the gut and soil employ different life-cycle strategies that result from genomic variations in the number of rap-phr signaling systems. Taken together, our results suggest that a spore quality-quantity tradeoff contributes to the evolutionary adaptation of sporulating bacteria.