In nature, continuous growth is key to the survival of any cellular species. But there is a price to pay for a constant rate of growth: aging. As a cell replicates (whether a single celled animal, or as part of a multi-celled one), it accumulates defects in its genome. Eventually, as these mutations build up, growth rates dwindle and the odds of cell death increase.
This has been the basic model of aging for several decades. Now, however, new studies of the venerable E. coli bacterium have revealed that– unlike all other aging models (single cells or animals) so far studied —E. coli “has a robust mechanism of growth that is decoupled from cell death.”
In a recent paper entitled ‘Robust growth of Escherichia coli’, published in the journal Current Biology, researchers discovered that E. coli bacteria are able to maintain a “steady state” growth rate despite the accumulation of genetic errors.
To achieve steady state growth, an emerging, bacterial colony undergoes exponential growth, which is maintained by the rate of elongation of each cell as it divides. This is true for cells that divide symmetrical or asymmetrically. However, this rate of elongation of bacterial cells decreases cumulatively with replicative age. Thus, it seems that a steady state population is sustained by individual cells that are not in a steady state.
To resolve this seeming paradox, researchers Wang et al of Harvard’s FAS Center for Systems Biology, analyzed 1 million E. coli bacterial cells utilizing a micro-fluidic device “designed to follow steady-state growth and division of a large number of cells at a defined reproductive age.”
They revealed the bacteria’s remarkably stable growth rate wherein each ‘mother cell’ inherited the same ‘pole’ (i.e., mitotic spindle orientation) for hundreds of generations. Researchers also found that E coli death is none-the-less predictable (non-stochastic), based on an accumulation of (genetic) damages.
The difference is that in this humble gut ‘bug’ the growth rate of each progenitor cell is stable right up to the moment of cell death.
For more information, visit the PubMed page here..
photo: USDA
