Growth phase-dependent priming of galactose metabolism in Escherichia coli

Bacteria routinely respond to changing environments, with vastly different with nutrient availability. When nutritional changes are predictable, bacteria can deploy mechanisms to anticipate them. In these cases, an organism's past environment can shape its response to its current environment, which is often referred to as a history-dependent behaviour (HDB). Using nutritional shift assays, we investigated how prior growth phase influences subsequent growth across different carbon sources. Here, we show evidence of a novel HDB regulating galactose metabolism in Escherichia coli, where previous growth to exponential phase leads to a growth advantage in a galactose environment, with no comparable effect observed in all other carbon environments tested. We demonstrate a role of the galactose repressors, GalR and GalS, in regulating this behaviour, as it is lost in strains deficient in either repressor. Further, we show how this HDB is generalizable across a collection of E. coli isolates, but not Salmonella - a closely related species with a similar natural history. Together, these findings build on the existing knowledge of HDBs governing carbohydrate metabolism by demonstrating how growth phase history can influence an organism's response to fluctuating nutritional environments.