T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Mould (Slime) Yellow

Slime mold or mould is a broad term describing some organisms that use spores to reproduce. Slime molds were formerly classified as fungi or protists, but are no longer considered part of these kingdoms.
Their common name refers to part of some of these organisms' life cycles where they can appear as gelatinous "slime". This is mostly seen with the myxomycetes, which are the only macroscopic slime molds.
Found in a wide variety of colours, more than 900 species of slime mold occur all over the world and feed on microorganisms that live in any type of dead plant material. They contribute to the decomposition of dead vegetation, and feed on bacteria, yeasts, and fungi. For this reason, these organisms are usually found in soil, lawns, and on the forest floor, commonly on deciduous logs. However, in tropical areas they are also common on inflorescences, fruits and in aerial situations (e.g., in the canopy of trees). In urban areas, they are found on mulch or even in the leaf mold in gutters, and also grow in air conditioners, especially when the drain is blocked. One of the most commonly encountered slime molds is the yellow Physarum polycephalum, found both in nature in forests in temperate zones.
Most slime molds are smaller than a few centimeters, but some species may reach sizes of up to several square meters and masses of up to 30 grams.
When food is abundant a slime mold exists as a single-celled organism, but when food is in short supply, slime molds congregate and start moving as a single body. In this state they are sensitive to airborne chemicals and can detect food sources. They can readily change the shape and function of parts and may form stalks that produce fruiting bodies, releasing countless spores, light enough to be carried on the wind or hitch a ride on passing animals.
Slime molds feed on decaying organic matter, bacteria, protozoa, and other minute organism which it engulfs and digests. The vegetative body of the slime mold is a plasmodium, an amoeboid mass of protoplasm which has many nuclei and no definite cell wall. In New Plymouth conditions, the creeping phase the common wood inhabiting slime molds dries into hardened structures producing dark masses of spore-like bodies and clouds of dust-like particles when body breaks apart. Some of the slime molds species are known to move into drier, more exposed locations in order to accomplish this life cycle change.
The spores, capable of surviving unfavorable weather, are spread by wind, water, mowers, or other equipment. Under cool, humid conditions, the spores absorb water, crack open and release a single motile spore. Each motile (swarm) spore feeds like the plasmodium undergoing several changes before uniting with another spore to produce an amoeboid zygote. The zygote enlarges, becomes multinucleate and forms a plasmodium.
Some species produce a stalk of hardened cells which other cells climb to create a fruiting structure from which spores are produced. This starts the cycle over again.

Photographed at Pukatea Dell  during  April.

 
Plasmodial stage of a slime mould  growing on a dead tree stump