Bacteria Enter Their Golden Years

Inevitable decline. Young E. coli (blue) grow faster and produce more offspring than old E. coli (red).

Woody Allen once said that he didn't want to achieve immortality through his work; he wanted to achieve it by not dying. Although that's unlikely for Allen and other higher organisms, many biologists believed that immortality was possible for microbes. Now, however, a new study suggests that bacteria get old, a finding that may give scientists a new tool for understanding aging.

The rod-shaped Escherichia coli bacterium divides in half to form two identical-looking daughter cells, which contain one old end, or pole, inherited from the parent and one new pole. When those daughter cells split, only two of the four resulting cells will have poles from the original cell. Current thinking assumed that all four cells were the same, and because they are essentially identical to the parent cell, immortality was possible for this organism.

To test this assumption, microbiologist Eric Stewart of INSERM in Paris, France, and colleagues tracked the fate of individual E. coli cells and their descendants. Using a specially designed microscope slide, the team took images of the cells every 2 to 4 minutes for up to 6 hours. Ultimately, they tracked more than 35,000 cells from 94 colonies. By comparing pairs of sister cells, the researchers discovered that cells that inherited the older end of the parent grew 2.2% slower than those that inherited a younger end did. The bigger the difference in age, the bigger the difference in growth rate, they report today in PLOS Biology--a result the team attributes to "decreased metabolic efficiency." The results "make it unlikely that natural selection produced an immortal organism," Stewart says.

Aging researcher Leonard Guarente of the Massachusetts Institute of Technology agrees and says researchers may be able to use E. coli to study "how aging occurs and how it's regulated." Biogerontologist George Martin of University of Washington in Seattle calls the results "conceptually very important" but says the cells that slow and stop reproducing may just be taking a break to repair themselves. If further study shows that the older cells are actually dying off, he says, it would "make biogerontologists take seriously the notion that there's aging in bacteria."

Related sites
The study
Background on senescence from Wikipedia
"Intimations of Immortality," an essay on the quest for scientific antiaging strategies, from Science