Biological complexity: bacteria seem to learn (Introduction)

by David Turell , Tuesday, March 08, 2016, 01:00 (3183 days ago) @ David Turell

In bacteria that are challenged with salt and then retested they seem to survive longer:-https://www.sciencedaily.com/releases/2016/03/160307153047.htm-Individual bacterial cells have short memories. But groups of bacteria can develop a collective memory that can increase their tolerance to stress.-***-Bacteria exposed to a moderate concentration of salt survive subsequent exposure to a higher concentration better than if there is no warning event. But in individual cells this effect is short-lived: after just 30 minutes, the survival rate no longer depends on the exposure history.-***-When an entire population is observed, rather than individual cells, the bacteria appear to develop a kind of collective memory. In populations exposed to a warning event, survival rates upon a second exposure two hours after the warning are higher than in populations not previously exposed. Using computational modelling, the scientists explained this phenomenon in terms of a combination of two factors. Firstly, salt stress causes a delay in cell division, leading to synchronization of cell cycles; secondly, survival probability depends on the individual bacterial cell's position in the cell cycle at the time of the second exposure. As a result of the cell cycle synchronization, the sensitivity of the population changes over time. Previously exposed populations may be more tolerant to future stress events, but they may sometimes even be more sensitive than populations with no previous exposure.-Comment: As the authors point out, cells are in different parts of their cycle. To me this is not a 'remembering' process. The sensitive cells seem to be culled out by their cycle position. Only a census of each cell and its cycle position will sort this out. But bacterial population size is definitely affected.