Yeast, algae and fungus, together for the survival of lichens

lichens are symbiotic relationship between alga and fungus

As we saw in a previous post about lichens, they need certain environmental conditions to be able to survive well and reproduce properly until colonizing the territory.

A lichen is the result of a symbiotic relationship between an alga and a fungus. However, scientists, after so many years studying lichens, have found a new discovery: in that relationship of two, there is a third, yeast. How is it that after so many years of study, scientists had not realized the presence of a yeast in this symbiotic relationship?

Symbiotic relationship between alga and fungus

lichen symbiosis between algae and fungus

Surely you have ever seen a rock with spots on its surface in your life. Stain whose colors can vary between black, brown, orange or green. You have also been able to see these spots on the roofs, on old houses, trees, etc. These spots that you have seen are lichens that are formed through an association between an alga and a fungus.

In nature there are various types of relationship between living organisms. We find living beings that are competent among themselves, others that are parasites and others whose relationship benefits both. More than symbiosis, the most appropriate technical word for it is mutualism. Mutualism is the relationship between the algae and the fungus that form the lichen in which the two parties gain from the relationship. What can both of you get out of this relationship?

In the life of a lichen, the algae plays the fundamental role of perform photosynthesis to be able to provide organic matter to the fungus. We pause briefly to explain that fungi are not autotrophic beings, that is, they do not synthesize their own food like plants. Mushrooms need organic matter to feed. This organic matter is contributed by the algae during photosynthesis. To return the favor to the seaweed, the fungus captures water and mineral salts from the environment where it lives, no matter how dry it is, and gives it protection against desiccation.

As we can see, this relationship is going from strength to strength. Both win and manage to survive in environments that are quite complicated.

How useful are lichens?

lichens in science magazine

We have seen the relationship that algae and fungi have to be able to form lichens. But what do we use lichens for? Lichens have been used throughout history for various purposes in which we find ourselves:

  • Manna lichen, which grows in North Africa and the Canary Islands, can be used as food. At the North Pole, reindeer and caribou feed on lichens.
  • In the pharmaceutical industry they are used to get antibiotics, vitamin C, and dyes, like litmus.
  • In cosmetics they are used to extract essences and perfumes.

I also want to mention that lichens are used today as indicators of contamination. As we saw in the previous post mentioned before, lichens require certain atmospheric and biotic conditions in order to survive. They are vulnerable to temperatures, rainfall, humidity, the presence of predators, etc. Well, this organism serves as an indicator of contamination. Being vulnerable to suspended particles caused by air pollution or water and soil, lichens do not grow in these places. Therefore, if we see that a place meets the right conditions for a lichen to survive well, and yet we do not see it, it will tell us that the place is contaminated.

Yeast as the third component of the relationship

yeast is the third component that forms the symbiotic relationship of lichens

We have seen what a lichen consists of and what uses it has for humans. However, what would you think if I told you that the algae and the fungus are not the only ones that exist in the relationship that makes up the lichen? From a lifetime, in schools, institutes and universities, whenever lichens have been studied, they begin by defining that it is a symbiotic relationship between algae and fungus. But recent studies confirm that there is a third component of the relationship: yeast.

On the planet there are more than 15.000 species of lichens and all of them have been studied on the basis that they are the result of the relationship between algae and fungus. But today, maybe it's time to start changing this idea. Yeast is part of this consortium between algae and fungus as a component of lichen. Scientists had not been able to detect the presence of this organism before even through powerful analytical magnifying glasses and after centuries and generations of studies.

The discoverers of this third component of the relationship have been postdoctoral research fellow Toby Spribille and his colleagues from the Universities of Montana in Missoula, Uppsala (Sweden), Graz (Austria), Purdue (USA) and the Canadian Institute for Advanced Research in Toronto. In order to make this discovery, they have been used in depth, apart from powerful microscopic observations, with genomic observations.

Study of lichens toxic to mammals

there are lichens toxic to mammals

This discovery has been on the cover of the magazine Science and supposes all a revolution for what was known about lichens and their behavior, survival, relationships, phenology, etc. This raises concerns for scientists about reassessing all the knowledge and assumptions that exist (even the most basic) about the way in which lichens form, about how they survive, what role each element of the relationship plays, about who plays what role. in symbiosis, and other issues.

Obviously, like almost all scientific discoveries, that was not exactly the object of study. The motivation of the scientists was to find out why two species of lichens are so closely related and living in the same ecosystem have such a drastic difference: one is toxic to mammals and the other is not. DNA analysis had only deepened the mystery, because the two species had identical genomes. Or so it seemed.

Yeast was discovered thanks to lichen DNA

yeast seen from the microscope

In order to explain this discovery, some elements of molecular biology must be mentioned. We begin because genes are made of DNA, but in order to activate these genes, the double helix of nitrogenous bases must be opened and a copy of one of its strands must be removed. This copy that we take out of the double helix is ​​not DNA since it only has one strand, which is why we call it RNA. Therefore, if one examines this strand of RNA, you are indirectly looking at the genes that are most active in that cell.

This is what these scientists were doing. They analyzed the RNA of these two species of lichens, in order to deduce why one was toxic to mammals and the other was not. Surely in the RNA sequence they could discover the reason for this situation. After the analysis of both RNAs, a quite remarkable difference was discovered: and the fact is that the RNA did not correspond only to the fungus known in the symbiosis, but also to another type of fungus, a yeast. This yeast has gone completely unnoticed for a century and a half of studies. In addition, the species of lichen that was toxic to mammals contained much more of this yeast than the species that was not toxic.

sequencing the DNA and RNA of a genome

In previous analyzes of other types of lichens, this yeast had been overlooked because they are very minority cells in this symbiont relationship. We only find one or two copies of DNA per cell. However, it has already been discovered that some of their genes are very active and can make hundreds or thousands of copies of RNA for each one of DNA. That was the key to success. And, indeed, it is the yeast that explains why one lichen is toxic and the other is not, despite the fact that they are identical in everything else.

Study of lichens around the world

scientists study the presence of yeast around the world

This discovery could be made in the lichens of Montana to discover why one was toxic to mammals and the other was not, despite having the same genome. Nevertheless, The researchers looked for the presence of this yeast in lichens around the world. From Japan to Antarctica through Latin America or Ethiopia. As they expected, the third component of this symbiotic relationship is found in all lichens in the world. It is a pervasive component of the most famous symbiosis in biology.

So from now on, when we define a lichen, we have to say that it is a symbiotic relationship between an alga, a fungus and a yeast (although yeast itself is a type of fungus), since this yeast has been present in all lichens throughout history, however, it has been hidden from all the magnifying glasses of scientists for more than 100 years. Scientists have surely detected it on other occasions, but have not realized it before.


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  1.   Ignacio Alberto Barra Alegria said

    Good afternoon, I would like to know if there is any type of bibliography on the subject...
    I'll look forward for your answer.
    Best regards