Not only does that potentially alter the fundamental definition of what a lichen is, but it “should change expectations about the diversity and ubiquity” of the organisms that form them, says a new study published today in Science.
The new yeast has apparently gone undetected in lichens for more than a century, despite the fact that scientists all over the world have devoted entire careers to studying lichens closely with microscopes and genetic testing.
That seemed so unlikely that the scientists working on the project had trouble believing it themselves.
“It’s so surprising that you kind of doubt yourself for a long time,” said John McCutcheon, a microbiologist at the University of Montana and a research fellow with the Canadian Institute for Advanced Research who co-authored the new study published today in Science.
“We had to check our data more than 10 times,” recalled Toby Spribille, lead author of the paper. “It seemed to me so unlikely that so many people would have missed that.”
Spribille, a University of Montana botanist who first started studying lichens in British Columbia 15 years ago, was inspired by a mystery flagged by B.C. lichenologist Trevor Goward in a series of essays.
It concerned two lichens that grow in B.C. and Montana and considered separate species for 100 years. One called wila or edible horsehair lichen, also known by the scientific name Bryoria fremontii, is a brown-coloured lichen that was an important traditional food for many First Nations in northwestern North America.
The other, called tortured horsehair lichen or Bryoria tortuosa, is yellow and poisonous. However, a recent genetic analysis showed that they were genetically identical — they were made up of exactly the same fungus and the same algae.
He brought the problem up with McCutcheon, an expert in new, sophisticated genetic techniques that he typically uses to study insects.
Traditional DNA analysis relies on probes or lures to fish out certain characteristic regions of genetic material, partly based on what scientists expect to find — like calling out names in a dark room to see who’s there, Spribille said.
McCutcheon says that gives a sense of what an organism is doing at any given time.
Further analysis showed it to be a new kind of yeast, belonging to the taxonomic group Basidiomycota, the same one that button mushrooms belong to. It was not at all related to the yeasts used to brew beer or bake bread. Yeast cells and DNA were extremely common in the yellow, poisonous lichen, but rare in the edible brown lichen.
After running the experiment enough to times to convince themselves the signal wasn’t due to contamination and pinpointing the yeast cells in the outer skin of the lichen, the researchers decided to see whether other lichens from around the world also contained the yeast. Sure enough, many did.
DNA analysis suggests the yeast has been part of lichens for more than 100 million years — since the end of the Early Cretaceous, when dinosaurs like spinosaurus and allosaurus roamed the Earth, and flowering plants first appeared.
Spribille said the discovery “seriously challenges” a lot of assumptions that have been held by lichenologists for a century.
Goward, whose essay inspired the research, said he was delighted by the discovery.
“It’s all very exciting to me,” he added. “If Toby’s idea proves to be correct, this is the second really major finding that changes how we see these organisms” — after the 1860s discovery that lichens weren’t one organism, but made of two separate organisms, an algae and a fungus.
Irwin Brodo, an emeritus scientist at the Canadian Museum of Nature in Ottawa who has devoted himself to the study of lichens for decades, said the discovery was “plausible” but “not proven yet.”
Brodo, who first gave the horsehair lichens the name Bryoria, said he was surprised that the new yeast cells were discovered in a part of the lichen that a lot of lichenologists, including himself, have examined carefully.
“I never saw them,” he said.