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Compound Eye

Compound Eye

The many facets of science photography

Starving to be Social: The Odd Life of Dictyostelium Slime Molds

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Dictyostelium discoideum stalking up into a fruiting body. Earlier stages of growth are visible in the background.

I like to think I have an active imagination, but Dictyostelium discoideum is an organism so bizarre I could not have dreamed it up on my own.

Dictyostelium is a slime mold. It spends much of its time as an apparently typical microscopic single-celled amoeba, oozing about in wet soil grazing on bacteria. Something truly odd happens, however, when the food runs out.

Here is John Bonner's classic time-lapse video of the slime mold in action:

Starving Dictyostelium band together to form a conglomerate organism. A multicellular slug of sorts, the group grows into a spore-making tower, a beacon for broadcasting amoebae out to richer grounds. The sudden lifestyle change is interesting enough, but the real evolutionary puzzle is the cells that comprise the delicate stalk. They die without reproducing so that cells in the fruiting body can turn into more effective spores. This form of altruistic sacrifice has fascinated biologists for decades. Here is an organism that is both solitary and fully, suicidally social, a near perfect model creature for understanding how multicellular life emerged from the amoebae.

I'm telling you all this because last week I had the fortune to visit the lab of Joan Strassmann and David Queller at Washington University in St. Louis. Strassmann and Queller head a research team dedicated to solving the Dictyostelium conundrum. I brought my photography gear, and below is a brief photo essay from an afternoon's shooting.

Joan Strassmann examines a plate of cultured Dictyostelium.

A clean lab culture shows the consequences of a low food supply. Amoebae at lower right congeal into slugs.

A slice through a culture plate shows a progression of slugs (at left) to fruiting bodies.

In a fit of aesthetic playfulness, I placed a sheet of red paper underneath a culture plate to bring a bit of color to the slug-filled microscape.

Blue paper is also interesting.

Pink might be my favorite pairing for slime molds.

A "mexican hat" appears as a slug begins to sprout a stalk.

A mature fruiting body above a plain of rising stalks.

This fruiting body has emerged (along with some extraneous stringy fungi) from a fresh dirt smear on a lab culture plate.

Different species of slime molds have different fruiting structures.

Organized slime! On reflection, I probably could have titled this post as such.

Update (11/28): Some people have expressed an interest in ordering prints of these images, so I have set up a gallery: Dictyostelium photographic prints. Click the "buy" button to explore sizes and framing options.


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The views expressed are those of the author and are not necessarily those of Scientific American.

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