Study

Basidiomycete yeasts in the cortex of ascomycete macrolichens

Spribille, Toby; Tuovinen, Veera; Resl, Philipp; Vanderpool, Dan; Wolinski, Heimo; Grube, Martin; McCutcheon, John P.

Science, 2016

Peer-reviewedgenomic studywild

What they did

Metatranscriptome sequencing of two chemically distinct but genetically near-identical lichens, followed by fluorescence imaging to locate the unexpected organisms found, and a survey across lichen taxa and continents.

Studied in: Bryoria fremontii, Bryoria tortuosa
Sample size: metatranscriptomes across lichen species and continents

What they found

A basidiomycete yeast was present in the outer layer of both lichens, in abundances tracking their chemical difference, and turned out to be widespread across macrolichens on six continents.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Many macrolichens are a symbiosis of at least three partners, not the two of the textbook definition.

How NatureHQ reads it

Lichens were the founding example of symbiosis and had been described as one fungus plus one alga for nearly 150 years. That two of the most-handled lichens in North America had a third organism sitting in their outer layer the whole time is a useful corrective about what "settled" means. It also explains a long-standing puzzle: two lichens that differ visibly and chemically while being the same species by every fungal and algal marker.

Limitations

Presence and abundance are established; the yeast’s functional role is inferred rather than demonstrated.
Not all lichens carry the yeast, and its importance likely varies.
Culturing the three-partner system to test the role directly remains difficult.