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Wednesday, June 16, 2010

Starving can be an advantage for slime molds

Slime molds (Dictyostelium discoideum) are amoebae that live in soil. Under normal conditions, they are single-celled organisms feeding on bacteria. However, when faced with starvation, they undergo a remarkable transformation.

The individual amoebae congregate into a multicellular slug and travel as a unit to a better location. When the slug finds a suitable spot, it transforms into a fruiting body with a clump of spores sitting atop a slender stalk. Remember, both the stalk and the spores were once free-living amoeba. Upon forming the fruiting body, the cells making up the stalk perish, whereas the cells that become spores live on. How do these jobs get divided up? Until recently, it was assumed that the first cells to run out of food would make up the stalk, whereas the cells who had the most food would become spores. In other words, the sickest cells would sacrifice themselves while the heartiest cells would continue on. It turns out, that’s completely wrong.

Jennie Kuzdzal-Fick and her mentors from Rice University carefully tracked the fates of individual D. discoideum cells as they progressed through their life cycle. To her surprise, the first cells to starve were predominantly the ones that became reproductive spores. Clearly, there is an advantage in being the first to stop eating and move into slug formation. Why, though, do the well-fed cells ‘agree’ to join the slug, only to become doomed stalk cells? The researchers are continuing to work on that question.

You can watch the slime mold life cycle below: