by Rodney McQueen and David Catchpoole

Even after many decades of research, the experts still debate how best to classify them.1,2 For many years the organisms pictured here were labelled ‘fungus’, because part of their life cycle is like that of many fungi. Mostly, though, they move and feed like one-celled ‘animals’. Yet they make their own cellulose, like a plant. And incredibly, as we shall see, there are times when they look and move like multi-celled animals. Part of their life cycle is also very similar to certain bacteria. Just what are they?

These are the so-called ‘slime moulds’, which are tiny (about 0.02 mm long, or 1/1000th inch), and despite their repulsive-sounding name, can look very beautiful. They are found all over the world, living in rich damp soil, leaf litter, or animal manure. They come in two broad types: plasmodial and cellular.3 We will mainly consider the cellular slime moulds, one of which, Dictyostelium discoideum, has been (and continues to be) the subject of intensive scientific scrutiny.4

Slime moulds vividly demonstrate the ingenious diversity of God’s Creation. It would be hard to imagine creatures more bizarre in their behaviour, if indeed it can be said that they ‘behave’.

Soil refiners

When conditions are favourable, slime moulds are free-living, single-celled, ameba-like micro-organisms. They are not actually ‘amebae’ as scientists would normally understand amebae to be (i.e. a type of protist, a one-celled organism). But they are so like them in appearance and form of motion that scientists usually call them by that name since no other suitable term is available. (This highlights the dilemma faced by scientists who try to ‘label’ these creatures within an evolutionary framework.)

Slime moulds creep about in or on the soil, leaf litter, logs or manure, consuming bacteria as they go. With their capacity for ‘self-cloning’ by dividing themselves into two new daughter ‘amebae’, slime moulds can rapidly multiply their numbers so as to exploit favourable environments. Each of these new amebae creeps off on its own as a completely separate entity. This can continue for as long as environmental conditions stay favourable. That is, as long as the ground is moist enough, and they can find enough bacteria for food….

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