Life, according to fungus
Recently, long white hairy fungi completely covering dog droppings were attracting interest at Doctors Point, Waitati, Dunedin.
Identification of this white fungal mycelium has proved very difficult, especially in the absence of reproductive structures such as sporangia. Many of these coprophilous fungi look similar, and fungus experts commonly culture them in a petri dish on a specific medium to produce all the reproductive features, such as sporangia and sporangiospores, so that the fungus can be identified to species level. This one may be a species of Mucor or
Absidia. It is most definitely not a
Phycomyces.
The most internationally wellknown dung fungus is
Phycomyces blakesleeanus, sometimes called a pin mould. This filamentous fungus has sporebearing sporangiophores borne on unusually long stalks, which have an acute response to a wide range of differing environmental stimuli such as light, gravity, wind, nearby objects and a range of chemicals.
This fungus became famous when, in the 1950s, Max Delbruck — a Nobel laureate who had done brilliant early pioneering work in molecular biology and on the DNA molecule — changed his research organism from bacteria and bacteriophages and began using
Phycomyces blakesleeanus.
Delbruck was a GermanAmerican biophysicist who colaunched the molecular biology research programme in the 1930s, searching for the chemistry and physics that underpin life. In Germany, a small group of physicists and biologists began to meet privately to find out the fundamental basis of life, by studying molecular biology. Delbruck’s small group included Nikolai TimofeeffRessovsky and Karl Zimmer. The work became widely known when Erwin Schroedinger, in Ireland, published a small book, What is life?, which was based substantially on Delbruck’s group’s work, some of which had been published in Germany in what was known as the ‘‘green pamphlet’’. Schroedinger’s book showed that since the large DNA molecules of living organisms followed the normal rules of physics and chemistry, it should be possible to work out the precise molecular structure of the genetic code. The book influenced many who sought to understand the DNA molecule, including Linus Pauling and James Watson who (with Francis Crick) worked out the currently accepted model of the DNA molecule.
Work on Phycomyces blakesleeanus has not provided anything of such fundamental importance as has bacteria and bacteriophages, but the fungus has become acclaimed for its response to stimuli including touch, wind and the presence of nearby objects, which it can perceive and bend and grow around, without physically touching. It grows towards light. It senses gravity by means of crystals that move about within single, very large sporecontaining cells (sporangiophores). A recent paper in PLOS Biology by geneticist Dr Gregory Jedd, at Temasek Life Sciences Laboratory, Singapore, found that these large crystals were derived from a fungus common ancestor with a bacterium hundreds of millions of years ago and subsequently put to a new use by the fungus.
Many organisms have sensors that enable them to distinguish up from down. Plants and fungi sense gravity in order to grow down to absorb nutrients and up to photosynthesise in light and to reproduce. Fungi (which are not plants) often produce spores only when their source of food is becoming low, and therefore a sense of gravity enables them to grow up to produce spores that can be dispersed freely. Most fungal gravity sensors are unknown. It was consequently a breakthrough to find that the dense crystals of Phycomyces blakesleeanus fall through the cytoplasm of cells that contain spores, thus enabling the fungus fruit body to sense where to grow upwards.
Phycomyces blakesleeanus belongs to the family
Phycomycetaceae of the order
Mucorales of the kingdom Fungi. Much important experimental work has been carried out on this fungus. This species has been found only rarely in New Zealand,
P. nitens being the species most encountered here.