 Bacillus subtilis
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June 30, 2003 — Some bacteria ensure their survival during famine by killing their siblings and eating them in order to avoid hibernating, an American-Spanish team has found.
The researchers, Richard Losik and graduate student Errett Hobbs from Harvard University in Boston, with Jose Gonzalez-Pastor of the Centro Nacional de Biotecnologia in Madrid, used Bacillus subtilis colonies which they had kept hungry by restricting nutrients.
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When nutrients start running out, one way bacteria cope is to enter into a kind of hiobernation, or resting state, for a long period. B. subtilis does this by creating an 'endospore' which can remain dormant for many years — up to a century if necessary.
But the researchers found that during the very early period of sporulation (creating the endospore), the bacteria produce an antibiotic to kill neighbouring bacteria that have not yet begun sporulation. This antibiotic breaks the cell walls of other bacteria open, releasing their nutrients, which the sporulating cell consumes.
The discovery of such cannibalistic behaviour by bacteria is reported in the latest issue of the journal Science.
Bacteria in a culture are genetically identical and reproduce asexually by creating spores — reproductive cells that detach from the original bacterium and eventually turn into new bacteria. But the process of creating the endospore uses up huge amounts of energy and takes several hours. Once begun, the process is irreversible; so the bacteria try to avoid it as much as possible.
The competition between bacteria means that if starving bacteria begin sporulating — but then nutrients become available again — they are committed to sporulating while the rest of the bacteria can keep growing and multiplying. In order to avoid sporulating, B. subtilis waits until the depletion of nutrients is prolonged before beginning sporulation.
The researchers found that when B. subtilis began the sporulation process (and before they reached the point of no return) they could stave off fully committing to sporulation by killing off some of their siblings and using their nutrients to survive. This means the cell can revert to growth rather than committing to sporulation.
The next step for the researchers is to establish whether killing of genetically-identical siblings is a widespread feature of the dynamics of bacterial populations.
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