The Cook Book

Recipe for the week of March 18 - 22

Living Spirals: Dictyostelium discoideum

Many of the mathematical recipes here in the Kitchen are motivated by real-world phenomena, so it is especially affirming when a physical system produces patterns and dynamics that are the spitting image of a CA rule. One celebrated biological example of an excitable medium is the early aggregation phase of amoebae in the surreal life cycle of a slime mold known as Dictyostelium discoideum, or Dicty for short. This week's soup is a colorized scan of spiral patterns generated during that phase. A little Web surfing reveals an active cadre of Dicty fanatics, seemingly concentrated in Germany and Texas. So here are some particularly interesting and amusing links to their arcane subculture.

For starters, a capsule summary by La Trobe University Microbiologist Paul Fisher (fisher@lumi.latrobe.edu.au):

Dictyostelium discoideum is a cellular slime mould whose natural habitat is soil and leaf litter where it predates bacteria by phagocytosis, grows and divides by mitosis. The Dictyostelium discoideum life cycle begins with differentiation of starving amoebae to a form where they become capable of synthesizing, secreting and being attracted by extracellular cAMP. The resulting aggregation process forms a multicellular migratory organism, the "slug", which migrates through a cellulose/protein extracellular matrix, the "slime sheath", that collapses behind to form a trail. Slugs are phototactic, thermotactic and weakly chemotactic. After a variable period of migration the slug stops and forms a fruiting body consisting, to a first approximation, of a droplet of spores supported by a tapered stalk and basal disc.

There is The Munich Dicty Site, a source of great little movies depicting the aggregation phase. We have lifted three of these which are quite reminiscent of our previous CA recipes for macaroni, multistrand spirals and spiral cores, respectively. Those of you with mpeg viewers can click on the thumbnails below to download and view the sequences:

Macaroni movie

Multistrand spiral movie

Spiral Core movie

Another hotbeds of slime is:

The Rice Dicty Site

(Eugenio has a Power Mac named Dicty, and offers a .mov flick for the Apple crowd).

But surely the preeminent archive of Slime Mold wisdom is


The Dicty Web Server
with an extensive bibliography, info on upcoming scientific get-togethers, lots of group snapshots, an email mailing list, and even some great sequences of Dicty Genetic Code.

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