Caulobacter crescentus
Image: microbewiki
Scientists from ETH Zurich have determined the formation of a collective memory in bacteria, which helps to deal with stress. A study published in the journal Proceedings of the National Academy of Sciences.
Microbiologists have conducted observations of several colonies of bacteria Caulobacter crescentus. First, scientists placed them in special containers, via which in one embodiment was leaking normal water and the other salt, with the concentration of sodium chloride in 80 millimoles. Then bacteria for different periods of time — from 45 to 160 minutes — transferred to an environment with higher salinity (100 millimoles).
It is known that after the bacteria were exposed to moderate stress, they are able to survive under more harsh conditions. For a single cell, this effect is short-lived and lasts less than an hour. However, if a lot of bacteria, the bacteria survival rate is high even after two hours.
As expected, in the experiment, bacteria which were previously in environments with lower salinity, better survive at higher stress than those found in ordinary water. However, the researchers found that the survival of bacteria depended on the time between moderate and more severe stress and had the oscillatory nature. For example, the maximum survival rates were in the intervals 45 and 120 minutes and the minimum at 90 and 150 minutes.
This effect can be observed if the exposure to salt causes delays in cell division and synchronization of the cell cycle in bacteria in the community. A special role is played by the exact stage of the cell cycle the bacterium was subjected to the second stress. Cells that for the interval between the stresses passed the stage of division, had a 70 percent chance of survival, unlike those that were in the middle of the cell cycle.
Scientists suggest that the collective memory of the stress is generated due to synchronization of cell cycles in bacteria. The more cells, the greater the likelihood that cells in the more severe stress will be in the “correct” phase of the cycle.
The cell cycle is called the period of the life of the cell from its formation in the fission of the parent cell until its own division. Cycle in mitosis consists of several phases — prophase, metaphase, anafazy and telophase at which the cell prepares its intracellular mechanisms for cell division.
