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Slimed and Consumed - The Blob is Real!

It's the season of darkness - rationalize your fear of those strange creatures found at your every turn

Fig. 1 Poster of the terrible 50’s horror movie that is The Blob. Image from: Wikipedia

The 1950’s were arguably the peak era for bad science fiction horror movies. There are the Godzilla movies, War of the Worlds, and a really bad Frankenstein remake. But the movie that sticks out most to me is The Blob, which is about a slimy mass that arrives from space. As you can probably guess from the movie poster above, The Blob subsequently proceeds to creep around and digest everything in its path, gaining size and strength until it has eaten the whole town.

As crazy as this idea may seem, there is in fact a small inkling of truth to this movie; some kinds of microbes will swarm to form a blob-like mass which migrates over land. But eating whole people – not so much. While some microbial “blobs” grow larger through the absorption of food, like The Blob, others form when solitary microbes huddle together and produce reproductive cells as part of an altruistic starvation survival strategy.

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Fig. 2 Look familiar? Slime molds such as the “dog vomit” mold shown here often appear as if from nowhere. The slime mold above is a plasmodial or acellular slime mold, meaning it is close to being one giant bag of cell contents. Image from: Wikipedia

These microbial “blob-formers” can either be eukaryotic (with the genetic material enclosed in a nuclear membrane sack, like us and plants) or prokaryotic (like bacteria, with the genetic material possibly bundled, but not held in a fully formed and closed nucleus). An example of a eukaryotic Blob is pictured in Figure 2, known as a “slime mold.” You may have noticed them appearing as if from nowhere on the surface of mulch around plants. The name slime molds is misleading because mold is an informal name for fungi (the causative agent of moldy bread), but slime molds are not fungi. In fact, slime molds have diverse origins and share more genetic material with other non-slime organisms than with slime molds [1].

Slime molds are bizarre because a common amorphous exterior can be derived from either a cellular or acellular interior. The acellular (“plasmodial”) ones are like The Blob in that they don’t have complete cell membranes. As a consequence, the insides of the cell (cytoplasm) can flow over large parts of their body. You can think of this as an alternative to our circulatory system; instead of blood, the cells mobilize their insides to rapidly move essential molecules to other parts of its “body.”

My favorite slime molds are cellular molds such as Physarum. When faced with starvation, these cells release and become sensitive to the signaling molecule cyclic AMP (cAMP). Other cells detect this signal, produce more signal themselves, and “join” the party, migrating to create a swarm of cells (Fig. 3). This migrating swarm or “slug” eventually forms a reproductive structure in which most of the cells will form a tower for a small subset of cells to disperse from. Those lucky cells at the top of the tower become haploid spores – hardy cells with only one copy of their parent’s genome – and disperse into the environment. These cells then germinate into amoeba-like cells and develop flagella (tails) which enable them to swim towards and merge with another amoeba-like cell. This is the interesting world of slime mold sex. Only select cells get to reproduce while the tower-forming cells are essentially sacrificed, making this a great organism to study cooperative reproduction.

Fig. 3 Watch slime mold cells find each other, form “slugs,” and create reproductive towers. (Video: John Bonner, Princeton University)

There are many other strange creatures you can find that look like “Blobs”: Globsters and jellyfish which wash up on the beach, jelly fungi which sometimes appear on people’s lawns, and of course the classic Halloween treats, frog eggs. While any of these could be the next star in a terrible science fiction movie, if you find something odd and “Blob-like” out in nature, there is almost certainly an expert who can help you figure out where it came from (see note below). While these organisms have minimal threat to humans, they can still be a little terrifying to encounter in real life!

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Fig. 4 Another kind of blob – a dead jellyfish washed up on a beach. When I saw these on the beach, I used to think people had put jello all over the beach for children like me to jump in. Image from: Wikipedia

Note: If you need help identifying something strange on plant or soil, most states have extension services with experts who can help. For example, the University of Massachusetts offers plant pathogen and insect identification services, and if you are in the neighborhood you can usually just drop in and someone will help you.

References:

  1. Nandipati, Satish CR, Kari Haugli, Dag H. Coucheron, Edward F. Haskins, and Steinar D. Johansen. “Polyphyletic origin of the genus Physarum (Physarales, Myxomycetes) revealed by nuclear rDNA mini-chromosome analysis and group I intron synapomorphy.” BMC Evolutionary Biology 12:166 (2012)

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