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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.

24Phages are the main source of within-species bacterial diversity and drivers of horizontal gene 25 transfer. Prophage cargo can determine ecological interactions of a bacterium with other 26 community members, and even its pathogenic potential, but we know little about the 27 mechanisms that drive genetic diversity of these mobile genetic elements (MGEs). Recently, 28 we showed that a sporulation selection regime promotes evolutionary changes within SPβ 29 prophage of Bacillus subtilis, leading to direct antagonistic interactions within the population. 30 Interestingly, SPβ belongs to the so-called phage regulatory switches that precisely excise from 31 the chromosome of sporulating mother cells, a phenomenon observed for phages infecting 32 diverse spore-forming species. Herein, we reveal that under a sporulation selection regime, SPβ 33 recombines with low copy number phi3Ts phage DNA present within the B. subtilis population. 34Recombination results in a new prophage occupying a different integration site, as well as the 35 spontaneous release of virulent phage hybrids. Analysis of Bacillus sp. strains suggests that 36 SPβ and phi3T belong to a distinct cluster of unusually large phages inserted into sporulation-37 related genes that are equipped with a spore-related genetic arsenal. Comparison of Bacillus 38 sp. genomes at global and local ecological scales indicates that these SPβ-like phages diversify 39 rapidly, especially in the absence of other MGEs constraining their lytic cycle. Our study 40 captures inter-phage recombination under an experimentally imposed selection regime, and 41 reveals the ubiquity of similar phenomena in Bacillus sp. genomic data. Therefore, our work is 42 a stepping stone toward empirical studies on phage evolution, and understanding the eco-43 evolutionary relationships between bacteria and their phages.44 45 46 47 72 4 specialised 21,22 transduction, respectively, thereby contributing to the spread of antibiotic 73 resistance 20 or virulence genes 23 . Although evidence from comparative phage genomics 74 indicates frequent recombination into new phage variants (so-called gene shuffling) 13,24,25 , this 75 is not reflected in experimental research. Phage recombination has been experimentally studied 76 using limited models, predominantly Salmonella typhimurium P22 with Escherichia coli 77 lambdoid phages 26,27 . Therefore, despite our knowledge of pronounced genomic mosaicism, 78 empirical research on prophage evolution is relatively limited. Combining such research with 79 broader comparisons of available host genomes may prove key to understanding the ecology 80 and evolution of bacteria and phages, including whether prophages serve as a major source of 81 bacterial within-species diversity, or as regulators. 82 Interestingly, certain prophages of Bacilli undergo genetic rearrangements upon 83 host development, acting as so-called phage regulatory switches (RSs) 28 . RS phages can switch 84 between integrated and extrachromosomal forms to modulate reproduction and surv...