Nine days after a heathland fire on Thursley Common near my home, the charred stems of gorse bushes sprouted pinky-orange, coral-like growths (top right). These did not appear on other charred plants. The little elongated cushions (middle right), each typically about 10 millimetres long but together covering whole stems, were quite powdery and seemingly only appeared after a brief, torrential downpour. Under the microscope (scroll to bottom right), they seem to consist of cells around 100 by 25 micrometres, often in chains like a string of sausages, and smaller cell debris. Can anyone explain what I saw? And what are the chains of cells, which appear to be undamaged?
Lots of people reckoned this growth was a slime mould, others suggested a yeast. But the most convincing answer came from several people familiar with forest fires 鈥� Ed
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The organism in the photographs is a fungus called Neurospora crassa. N. crassa is found growing on the burnt boughs of trees following forest fires. It is a non-pathogenic saprobe 鈥� an organism that gets its nutrition from dead and decaying plant matter. The spores gain access to the caramelised plant sap below the bark through cracks caused by expansion during forest fires.
鈥淭he fungal spores gain access to the plant sap through cracks in the bark caused by forest fires鈥�
In the lab, it has been discovered that the ascospores (sexual spores) of N. crassa require an hour of incubation at 60 掳C to bring them out of their dormancy which, in the wild, occurs during cooling after a forest fire.
The orange stuctures are the vegetative spores, or macroconidia, which take approximately one week to reach maturity.
Microscopically, the fungus appears as long filaments, or hyphae, which are partially divided into compartments by walls with pores through which organelles can pass. On maturity, the apical portion of the hyphae grows vertically and is subdivided into lots of little compartments, each of which is a spore. The spores remain linked in chains until they are dispersed by wind.
N. crassa forms an essential part of the ecosystem in areas that are prone to forest fires, by contributing to the degradation of burnt plant matter.
Tejaswini Dhavale, Singapore
Neurospora is usually found growing 10 to 14 days after a fire, and is fairly common around the world. The visibly orange, fluffy part of the fungus is the macroconidia. These are the mitotic non-sexual spores of the fungus.
This is an impressive fungus with a rich history, and it is a model organism in the lab. It was used in the 1958 Nobel prize-winning research done by George Wells Beadle and Edward Lawrie Tatum when they secured the award for physiology or medicine.
The following is a web page on all sorts of Neurospora information:
Chris Villalta, Berkeley, California, US
The orange blooms seen after the burning of vegetation are the ascomycete fungus Neurospora. It was thought that Neurospora was mainly restricted to the moist tropics and sub-tropics, but recent studies have found such blooms on vegetation in much more diverse habitats. It has been discovered as far north as Alaska. For a recent publication on this, see
Alan Radford, Faculty of Biological Sciences, Leeds University, UK