After leading a recent walk at Fernandez Ranch in Martinez for the California Center for Natural History I found myself back out on the same trail just a few hours after the hike finished. Often when leading walks one doesn’t have the chance to be still in nature and I returned to do just this. Being still, though, doesn’t mean being stationary, it is the stillness of mind experienced when the desires of others and my own mixed up in a social soup aren’t sloshing around back and forth in my head and I’m free to use that extra bandwidth to see more of what is around me.
The green hills glow in the slices of evening sun that manage to cut between remnants of a soft northern California storm. Chartreuse ribbons run the edges of hills where the grass has already started to fade while the slopes falling into the ravines are still a dark verdant green. In these ravines, sun down, my eyes become less useful beneath the bay trees and coast live oaks that block out what is left of the afterglow and hallucinations briefly take over as my neural networks amplify the other sensory channels in order to perceive again the world around me. In the distance a faint green glow from the belly of an oak catches my eye and I approach expecting to find nothing but my own mis-firing cone cells. However, a great cluster of Omphalotus olivascens, also known as the Western Jack O’Lantern mushroom due to its bioluminescence, piles out of the wounded trunk, illuminating the area right around it. In the darkness of night the world feels cavernous and suddenly with this little bit of light to hang the entire universe upon the world feels enormous, open, and alive.
Bioluminescence is not just restricted to the Kingdom of fungi, but can be found across many different taxonomic groups. Anyone that has spent time east of the Rockies is likely familiar with fire flies, being neither full of fire or flies. The word "luminescence" means to emit light without heat or fire and was first coined by physicist Eilhardt Wiedmann in 1888 (1), although observations of luminescence are described as far back as Aristotle’s De Anima of 350 B.C (2) and the Shih Ching whose poems were written between 10,000 and 15,000 BC (3). In California we have fireflies (Family Lampyridae), but the adult stage isn’t what glows. Instead, the larval stage is what you are most likely to find in the forests at night due to their bright green light.
Along coastal California you even have the possibility of seeing the waves glow at night due to Dinoflagellates in the warmer months, although I’ve seen them in November along the San Mateo coast. I’ve even heard reports of Lake Merritt in Oakland giving night time rowers a glowing lip to their oars. Among the dock-fouling organisms of the San Francisco Bay it is possible to find the Dwarf Brittle Star (Amphipholis squamata) that generates light to scare off predators. Porichthys notatus also known as the Plainfin Midshipman is an intertidal fish along our coast that uses its bioluminescence as counterillumination so that at night when it is active predators swimming beneath it do not notice its silhouette the light produced allows it to blend into the diffused moonlight. It obtains its bioluminescence most likely from a diet of bioluminescent Crustaceans known as Ostracods (4). Deeper yet in our ocean we find Aequorea victoria, a glowing Jellyfish whose Green Fluorescent Protein (GFP) has been a cornerstone of the Cell Biologist’s toolbox as linking it to proteins of interest it makes it easy to visualize their location in a cell or an organism and has led to many breakthroughs in developmental biology. Even deeper yet in our waters are fish that host bioluminescent bacteria in specialized organs which they use to draw prey close, the best example of this are the Anglerfish of the Order Lophiiformes.
Many of the organisms that produce their own light use a luciferase enzyme to oxidize a class of molecules called luciferins. The structure of luciferins varies widely among the eight known types, but all of them produce oxidation states that emit light upon decaying down to their ground state. The luciferin from fungi has only been recently elucidated and is derived from Hispidin, a common molecule in fungi and plants(5). The yellow to orange color of many fungi, potentially including Omphalotus olivascens is due to the presence of hispidin and overtime oxidizes to a dark brown (6). Hispidin in fungi may be one of the primary molecules leading to fungal lignin, the material that gives old mushrooms their sturdiness. Precursor molecules to Hispidin are key to the pathway to build lignin in plants, the structural molecules that help give vascular plants their rigidity(7).
It is no surprise then that when the fungi of the world are surveyed for bioluminescence they all fall within those that degrade wood for their primary food source, as part of the breakdown most likely frees up luciferin precursors. Across the globe there are at least 64 species of bioluminescent fungi and they occur in many different groups, but seem enriched in Genera Mycena, Omphalotus and Armillaria (7). Fungi all appear to bioluminesce between 520 nm and 530 nm, which many insects have very sensitive photoreceptors for(8) and in experiments by Sivinski fungal bioluminescence increases the number of arthropods found in an area dramatically (7). In California the Western Jack O’Lantern is the most commonly encountered bioluminescent mushroom, but there are reports of Honey Mushrooms (Armillaria) and the Bleeding Fairy Helmet (Mycena haematopus) having low amounts of bioluminescence in the fruiting bodies and mycelium. There is so much to see out there that illuminates the night and the things we don't know, so get out there and explore.
Valeur, Bernard. Introduction: On the Origin of the Terms Fluorescence, Phosphorescence, and Luminescence. Springer-Verlag Berlin Heidelberg. 2001.
Aristotle. De Anima (Book II, Chap. 7, Sec. 4)
Legge, James. The Chinese classics 4:237, 1893. The Odes of Pin, III, verse 2
Purtov, K. V., Petushkov, V. N., Baranov, M. S., Mineev, K. S., Rodionova, N. S., Kaskova, Z. M., Tsarkova, A. S., Petunin, A. I., Bondar, V. S., Rodicheva, E. K., Medvedeva, S. E., Oba, Y., Oba, Y., Arseniev, A. S., Lukyanov, S., Gitelson, J. I. and Yampolsky, I. V. (2015), The Chemical Basis of Fungal Bioluminescence. Angew. Chem. Int. Ed., 54: 8124–8128. doi:10.1002/anie.201501779
Perrin, Peter William. The Cinnamic Acid Pathway and Hispidin Biosynthesis. Phd Thesis. University of British Columbia. 1968
http://cronodon.com/BioTech/Insect_Vision.html. Accessed 2016.12.30