Enhancement of K-strategy evolution in histidine utilization using a container with compartments.

Evolutionary strategies in growth improvement can be classified into r- or K-strategies. The former strategy corresponds to an evolutionary increase in growth rate, whereas the latter corresponds to an increase in the maximum amount of organisms or carrying capacity. What determines the strategies to be adopted during evolution? Spatial structures that compartmentalize the population into small patches are key to inducing the K-strategy. Interestingly, previous evolution experiments using Escherichia coli in a glucose-limited batch culture showed that carrying capacity could improve evolutionally even in the absence of spatial structures. However, it is unclear if the lack of spatial structures can direct evolution toward high carrying capacity for utilization of other resources. To address this question, we established a simplified evolution experiment using histidine-requiring E. coli grown under histidine limitation in a container with compartments. We confirmed the importance of spatial structures in K-strategy evolution in histidine utilization. Whole genome sequencing of the K-adapted strains showed functional variety of the mutated genes during the fitness-increasing period. These results validate the importance of spatial structures and imply that restriction of K-strategy evolution on a sort of nutrients is attributable to a paucity of appropriate selection rather than a paucity of causal mutation.