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The Remarkable Lives of Slime Moulds

Slime moulds sit somewhere in the middle of the subterranean food chain. They pursue and eat bacteria while being chased and eaten by worm-like nematodes. When food is abundant, they move about as single cells. However, when food runs out, tens of thousands of cells clump together into a giant slimy blob.

The ultimate goal of a slime mould is to form spores. Spores may lay dormant for years and only hatch into new cells once conditions improve, thus resetting the life cycle.

Experimental biologists love to work with slime mould even if it looks like dog barf. They’re so loveable because they share many genes and protein components with mammalian cells, they can exhibit similar behaviours and are much easier to grow in the lab. To make some slime, you simply harvest some spores into a dish filled with a simple sugary broth, allow the population to grow for a few days and—boom!—time to experiment. 

Do this with Dictyostelium discoideum cells, for example, and you can start answering fundamental biological questions like: 

  1. How do cells orient themselves and move in their environment?
  2. What happens when a cell is hijacked by a pathogen like LegionellaMycobacterium tuberculosis, or Salmonella

Remove the sugary broth, and tens of thousands Dictyostelium stream together into a central blob, rearrange themselves into a slug and move towards the soil surface. They then undergo one final rearrangement, hoisting a ball of spores into the air by pushing a stalk into the ground (see video below). Now you have access to a whole suite of new questions: 

  1. How do cells communicate with one another? 
  2. How do cells become specialized? 

Some slime mould is being used to answer very different questions. Physarum polycephalum, which translates fittingly into "many-headed slime", sets out en masse to find its fungal food source. They do so with such staggering efficiency and eerie beauty that some scientists have assigned Physarum "semi-intelligent" status. If you watch Heather Barnett's 2014 TED talk, you might draw the same conclusion.

Barnett presents results from experiments that suggest slime moulds are capable of problem solving, of learning and even of solving the travelling salesmen conundrum. Whether this is truly evidence of intelligence or simply of awestruck scientists rewarding a lofty label to something they do not fully understand is open to debate.

In any case, I think we can agree with slime mould research pioneer John T. Bonner's view that these are, "...remarkable feats for a bag of amoebas."
 

For an introduction to Dictyostelium, head to this picture and video page. Visit Science World Resources for related hands-on learning opportunities.