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I know that the cells of mammals at least stop dividing when they are old, and then die a programmed cell death. Then other cells have to replace them.

But in a bacterial colony, each cell replicates for itself. Obviously, if a division of a bacterial cell of generation N were to produce two new cells of generation N+1, and all bacteria died of old age at generation M, there would be no bacteria left around.

So how is it regulated in bacteria? Are their divisions simply unlimited? Does a cell never die and just divide forever?

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This is a interesting question and for a long time it was thought that they do not age. In the meantime there are some new papers which say that bacteria do indeed age.

Aging can be defined as the accumulation of non-genetic damages (for example oxidative damage to proteins) over time. If too much of these damages are accumulated, the cell will eventually die.

For bacteria there seems to be an interesting way around this. The second paper cited below found that bacteria do not divide symmetrically into two daughter cells, but seem to split into one cell which receives more damage and one which receives less. The latter one can be called rejuvenated and seems to make sure that the bacteria can seemingly divide forever. Using this strategy limits the non-genetic damage to relatively few cells (if you consider the doubling mechanism) which could eventually die to save the others.

Have a look at the following publications which go into detail (the first is a summary of the second but worth reading):

  1. Do bacteria age? Biologists discover the answer follows simple
    economics
  2. Temporal Dynamics of Bacterial Aging and Rejuvenation
  3. Aging and death in an organism that reproduces by morphologically symmetric division.
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protected by The Last Word Feb 13 '15 at 9:13

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