Figure 2.

Mechanisms implicated in microbial history-dependent behavior. Chromatin state, protein inheritance and cellular metabolic state have all been described to underly history-dependent behavior. Semi-stable changes in chromatin state of promoters of specific genes can persist across environments, thus allowing cells to respond faster when that specific environment returns. Triangles indicate generic histone modifications, Ac (dark green circle) indicates acetylation and Me (dark orange circle) indicates methylation. In case of protein inheritance, proteins can remain stable and active over multiple cellular generations and/or across environments (via both symmetric and asymmetric protein inheritance). Also cellular metabolic state can play a role in history-dependent behavior, with for example a cell’s respiratory activity/capacity being a key factor of history-dependent behavior for carbon source changes. Figures depict the different mechanisms described, with examples of conditions in which this type of mechanism has been suggested to underly the observed history-dependent behavior. Cells indicated with a dark brown contour in the returning environment will show history-dependent behavior and thus be able to overcome the environmental change faster. For more details, see text.