Foxfire: Chemistry of the undead



Ghostly mushrooms



I am currently approaching the half way mark in my current work-in-progress (WIP-2) and have been making particularly heavy use of foxfire.  I didn't start out to write about that... in fact, this book started out as a humorous middle grade adventure and quickly turned into a dark, YA biopunk.  Write what you know, I suppose.  One of the emerging themes is the struggle between the protagonists and the technologically-advanced fungi that exists in their (slightly dystopian) world.  So, I found it a little coincidental that a report came out a week ago by Marina Capelari and colleagues about a type of ghost mushroom that had been re-discovered in a Brazilian rainforest after being extinct for over 150 years (abstract in the journal Mycologia).  The mushroom, formerly known as Agaricus gardneri, is notable for its bright and constant bioluminescence.  To understand why this is unusual, here is a brief description of how foxfire comes to be:

Bioluminescence is generally accepted to come from a 2-step reaction.  A chemical called luciferin (L) is first reduced (to LH₂) and this reaction is catalyzed by an enzyme called reductase.  NADH is a molecule (di-nucleotide, actually) that is a cofactor in many redox reactions.  Its basic function is to move protons around (you're a geek if you noticed the chemistry pun).

L + 2NADH <--> LH₂ + 2NAD+

Reduced luciferin is then oxidized (to LO) by an enzyme called luciferase.  This process also produces a photon of light and is the source of the creepy glow.

LH₂ + O₂ <--> LO + H₂O+ LIGHT



Illudin S: Potential substrate for ghost fungi

Why am I cryptically showing fungal luciferin as L, instead of showing the chemical structure?  Could it be that my chemistry skills are so bad, I couldn't tell the difference between L and LH if my life depended on it?  Well, yes -- but it is also true that the luciferase substrate in fungi is not well characterized. The luciferin for A.gardneri is probably a member of the sesquiterpene family, most likely an illudin.  Some of these compounds have been studied as anticancer agents but the illudins tend to be extremely toxic (possibly another reason they are called ghost mushrooms!).  Interestingly, other luciferins (such as those found in fireflies, shrimp, etc) have totally different chemical structures, which gives them different biological properties and unique spectral characteristics (ie, different colors, brightness, etc).  Changes in the luciferin structure, amino acid substitutions in the active site of luciferase, and varying levels of oxygen or water can each contribute to changes in the emission of light.  What is unusual about A. gardneri is that unlike other species, the bioluminescence is almost constant.  In fireflies, the luciferin is released when they want to blink and in the case of other species, they light up only after contact (probably a means of self-defence).  So why does this mushroom glow all the time? No one knows yet.  The biochemistry of these things is almost as mysterious as seeing their eerie ghostly glow on some rotting tree stump at midnight.

However, it provides a great real-world example of the potential technology for my story.  It doesn't take much imagination to think that these mushrooms could be engineered to be very bright or to respond in controlled ways depending on environmental input.  A basic example from my WIP is that these types of fungi are used for lighting underground.  No electricity required, no pollution, and little maintenance.  They are almost the perfect type of lighting... or are they?  Anyhow, I thought it was a pretty clever idea early on until I found out that Ben Franklin used foxfire from mushrooms to light the inside of one of the first submarines.  Was there anything this guy didn't know about?  I guess he's going to have to go on my list of card-carrying biopunks.