Figure 1.

Principle of microbial history-dependent behavior. (A) A cell’s behavior can depend upon past experiences, a phenomenon termed history-dependent behavior. Cells encountering a specific environment need to adjust to that environment. Some cells are able to adapt faster based on their past experience, and thus display a strong history-dependent behavior. For example, when a population of cells encounters a specific environment (environment 1) again, there is a fraction of cells that can respond and adapt faster to this environment than others. These cells, indicated with a dark brown contour in the returning environment 1, display such history-dependent behavior. (B) Duration of the lag phase is an ideal read-out for history-dependent behavior in changing carbon environments. When shifted from one carbon source to another, yeast cells need to adapt their metabolism and express genes required for consumption of the specific carbon source present. This necessary adaptation often leads to a period of no or reduced growth (as visualized by a delay in increase of population density), called the lag phase. Not only the environmental change as such influences the lag phase length, but the lag phase length upon return of environment 1 (E1, indicated in yellow color) can also be influenced by how long ago the cells have been exposed to environment 1, with longer times spent in an intermediary environment 2 (E2, indicated in brown color) resulting in longer lag phases when the original environment 1 returns.