Back in 2009 I wrote a little article about lichen, those symbiotic organisms that have intrigued biologists for so long. At the time I wrote the piece, it was generally believed that lichen were usually a partnership of two species, a fungus and a bacteria, though some were known to have more than one bacteria in the group. It turns out that this is not true.
You can easily see how this theory came to be so widely accepted by simply looking at a slice of lichen under a microscope. Here you can see the different organisms that cooperate to create a lichen.
In this image you can see the photosynthesizing bacteria arranged just beneath the surface to catch the light, while the supporting fungus, here stained blue, lives below.
The species pairings are usually quite specific; for each fungus there is one bacteria that will join with it to create a lichen. It would seem, therefore, that each unique pairing would produce a specific lichen. But this is not always the case – apparently different lichen are sometimes made of the same symbiotes. Moreover lichenologists who have attempted to combine two species known to coexist in real lichen, have not been able to graft the two species together to create a viable lichen. Why?
The situation intrigued Dr. Tony Spiribille who has been studying lichen for over 15 years. He was particularly interested in two North American lichen which contain the same symbiotes, but which are different in several ways. Bryoria fremontii, sometimes called “Tree Hair Lichen” is a dull brown and looks like thick hair.
Bryoria tortuosa is yellow or greenish yellow and has finer threads.
Bryoria fremontii is is edible – Bryoria tortuosa is poisonous.
Thinking that these two lichen must be different in some way, Dr. Spiribille sequenced their DNA. But DNA from the two lichen appeared to be genetically indistinguishable! Clearly a closer look was called for.
Working with another group at the University of Montana, Dr. Spiribille used advanced sequencing technology to run RNA “deep scans” of the two lichen. Surprisingly, the RNA scan revealed the presence of a third species that was present in both lichens. Believing that his samples had somehow been contaminated he repeated the experiment, several times, but the third species always showed up. It is a species of Basidiomycetes fungus, previously unknown. He found that the Basidiomycetes fungus produces the substance that makes B. tormentosa so toxic. B. fremontii has the fungus, but very little of it, so it is safe to eat.
Dr. Spiribille then asked other lichenologists around the world to look for the Basidiomycetes fungus. Amazingly, they found it in every lichen they examined – i It has now been found on every continent on earth. Moreover molecular evidence indicates that it has been part of lichen symbioses from the start of this partner’s evolution. Unnoticed for almost 150 years, this single species of fungus appears to play an important role in the lives of lichen everywhere. Dr. Spiribille’s remarkable discovery now points the way to a whole new area of research, one which we didn’t imagine just a few years ago.