A Microbial Biorealm page on the genus Panellus stypticus
Fungi; Basidiomycota; Agaricomycetes; Agaricales; Mycenaceae; Panellus; Panellus stipticus
Description and significance
Panellus stipticus is a sometimes luminous mushroom found in a variety of habitats all over the world. Those in North America have been found to be luminescent while those on other continents are non-luminescent. The cap of this mushroom can range from ½ to 1¼ inches and is cinnamon colored. Its form is convex and its shape is subreniform (shaped like a kidney) with a woolly surface. The gills are a similar cinnamon color to the cap and are narrow and crowded. The lateral stem/stalk is a paler color than the cap and gills and is short and compressed. It is 6-12 mm long and 3-8 mm thick and is also covered with a powdery secretion. P. stipticus’s spores are oblong and white measuring 3-4.6 x 1.2-2.2 μ. The light of P. stipticus is a greenish white color and emanates from the gills, cap, and mycelium. There have been accounts of luminous mushrooms bright enough to read by and troops serving in New Guinea described them as “green eyes staring into the darkness.” It has also been written that people in Scandinavia used to use the mushrooms to find their way in dark woods. In medical history, P. stipticus was used as a blood thickening agent to stop wounds from bleeding. In fact, “stipticus” can also be written as “stypticus” referring to its styptic properties.
Not very much information is known about the genomic structure of P. stipticus, but it is clear that its luminescence is an inherited dominant trait (see next section). An interesting feature of Panellus stipticus is that it has a group I intron in its ribosomal small and large subunits.
Cell structure, metabolism & life cycle
P. stipticus has a heterothallic, tetrapolar mating system in which luminosity is an inherited dominant trait. Luminescence is greatest when two luminescent individuals are mated and lowest when two non-luminescent organisms are mated. P. stipticus has a maximum luminescence of 525 nm and peak luminescence from the hours of 6:00-9:00PM. Luminescence has also been found to correspond to developmental stages. For the first 6-10 days, the organism is non-luminescent, but it is in its primary growth phase. The next 3-5 days usually shows a rapid increase in luminescence, which coincides with the end of linear growth. This is followed by a quick decline in luminescence as the organism ages. Lastly, in most cultures there is a secondary increase in luminescence signaling the development of fruiting primordial. In order for an organism to be bioluminescent it must be capable of oxidizing luciferins (organic substrates) with enzymatic luciferases to produce an unstable compound that emits it excess energy in the form of light as it decomposes. In the case of P. stipticus, it is believed that there are two enzymes involved and so it is therefore thought that there must be multiple genes required for luminescence. It is also possible that these genes are subjected to regulatory mechanisms as well.
Ecology (including pathogenesis)
P. stipticus grows on hardwood in the spring through the fall. It is found in many places all over the world and it is grouped into two major clades: the Northern Hemisphere clade and the Oceanian clade. Studies have shown that, while only those mushrooms found in eastern North America are luminescent, those growing in North America, Russia, Japan, and New Zealand all stem from a single species. It is most probable that the Oceanic collections of the species were derived from the Northern Hemisphere collections because the specimens collected in Oceania have a restricted gene pool pointing to a founder event. Besides geographical difference, the medium that P. stipticus is grown on has an effect on its luminescence. If it is grown in a completely liquid culture, it is non-luminescent, but the longer it is grown on a solid medium, the more luminescent it is. It is the most luminescent when it is grown in the dark and, when in the dark, it is brightest in the center, in contrast with its bright periphery when it is grown in the light (although florescent light inhibited growth and luminescence). In addition to growth medium and light intensity, P. stipticus prefers to grow at 28°C and a pH of 3.8. Its best carbon sources include glucose, maltose, trehalose, cellobiose, and pectin and its best nitrogen sources include ammonia and asparagines. The evolutionary reason for P. stipticus’s luminescence is still a mystery, but some scientists have made hypotheses based on the evidence that the light attracts arthropods. Because of this fact luminescence may serve to attract spore dispersers, attract carnivores that prey on arthropods, warn fungivores of unpleasant taste, attract fertilizing organisms, or repulse negatively phototropic fungivores.
Panellus stipticus is a white rot fungi, which is a basidiomycete that degrades the lignin component of lignocelluloses resulting in bleached wood giving it a distinct white color. In order to break down lignin, white rot fungi use several enzymes including lignin peroxidase, manganese peroxidase, laccase, glyoxal oxidase, and veratryl alcohol. White rot fungi are often used in bioremediation because of their high tolerance of toxicity and their ability to withstand high temperatures and a wide range of pH. Their high toxicity tolerance stems from that fact that lignin and the enzymes that degrade it are nonspecific so they are also able to break down hazardous compounds such as polycyclic aromatics, polychlorinated biphenyls and dioxins, DDT, and chlorinated phenols. Panellus stipticus itself has been found to be capable of reducing the amount of phenolics in the wastewater created by green olive debittering and it is able to degrade dioxin with a 100% decrease in 2,7-dichlorodibenzo-p-dioxin after being exposed for 40 days.
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