Tag Archives: lichen

Lichens are having a hard time catching up to climate change

Lichens are some of the most inconspicuously amazing organisms out there. They’re essentially composite, symbiotic organisms made from a fungus and algae or cyanobacterium living among the filaments of fungi. Lichens can grow almost everywhere, from the Arctic tundra to the bark of a tree in your backyard. However, this apparent resilience is being challenged by the climate crisis, with a study showing they have a very tough time adapting to rising temperatures.

Image credit: The researchers

Matthew Nelsen from the Field Museum in Chicago and his colleagues investigated how the climate preferences of lichen change over time and how this relates to the climate crisis. As it turns out, they shift temperature preferences by less than 1ºC every million years. This is lower than the global warming of up to 3ºC predicted.

“Our initial motivation was to better understand how this important group of algae had diversified to collectively occupy an extremely wide range of climates across the globe,” Nelsen told ZME Science. “It was an exciting opportunity for us to use the past to make predictions about how these algae may be affected by modern climate change.”

Exploring lichens

Nelsen and colleagues focused on a single genus of algae, Trebouxia, which is found in about 7000 species of lichen. When algae take residence inside a lichen, they live with the fungus as one — each providing something that benefits the whole. The algae provide food through photosynthesis, while the fungus provides the physical structure.

The team gathered plenty of data on where Trebouxia occurs across the world, observing the climate conditions of each location. They also worked with a database of Trebouxia genes to create a family tree for the algae. All this information was then used to estimate how fast Trebouxia has adapted to a changing climate in the past.

They found that the change in the climate preferences of the algae happens very slowly over the course of millions of years. This means that Trebouxia is likely to be impacted by the fast climate change that the planet is currently going through. If they can’t adapt fast enough, they might have to modify at least part of their current range.

The researchers believe that lichens that rely on Trebouxia will likely disappear from many of the places they are found today. Some might migrate to other places with more tolerable climate conditions, but environmental degradation caused by humans also means that there are limits to the area where the lichens could spread into.

Fewer lichens would have deep consequences on ecosystems, as they are the dominant vegetation on 7% of the Earth’s surface, Nelsen said. They are important for ecosystem hydrology as well as for carbon and nitrogen cycling. But there’s no need to despair. We can still reduce our emissions and do further research on lichens, he said.

“One question that has repeatedly come up is whether the fungal partners exhibit a similarly low historic rate of change.  This would be especially interesting to pursue,” Nelsen said. “It would also be wonderful to have experimental data demonstrating the thermal limits and optima of these algae to gain a better understanding of them.”

The study was published in the journal Frontiers.

Lichens actually comprise a threesome, not a partnership

When the nature of lichens was discovered 140 years ago, they became the most prominent example of symbiosis, a term that defines a mutually beneficial relationship between two dissimilar organisms.

Image credit Pixabay

Image credit Pixabay

In the case of lichen, the filaments of a single fungus create protection for photosynthetic algae or cyanobacteria, which provide food for the fungus in return. However, a new study reveals that there is actually a third organism involved in this relationship – a yeast that likely provides the structure for “leafy” or “branching lichens.”

“These yeast are sort of hidden just below the surface,” said John McCutcheon, a genome biologist at the University of Montana, and senior author of the study. “People had probably seen these cells before and thought they were seeing something else. But the molecular techniques we used happened to be especially good for spotting the signal of a separate organism, and after years of looking at the data it finally occurred to us what we were seeing.”

McCutcheon’s team made the discovery after studying two lichen species obtained from Missoula, Montana mountains – Bryoria fremontii and B. tortuosa. Despite B. tortuosa possessing a yellow color due to the presence of vulpinic acid, genetic tests revealed identical fungus and alga in both species. However, they also discovered the genetic signature of a third species – a basidiomycete yeast – in both species, although it was more abundant in B. tortuosa.

Additional testing of 56 different lichens from around the world revealed that each one has its own variety of basidiomycete yeast, suggesting that lichens actually comprise a threesome, not a couple, essentially rewriting 150 years of biology.

The team believes that this newly discovered yeast could play a role in creating the large structures seen in macrolichens, which would explain why these particular lichens are hard to grow in the lab when using just a fungus and alga.

“This doesn’t prove that they’re necessary to create the structure of the macrolichens, or that they do anything else for that matter,” McCutcheon said. “But its early days. It took a lot of work just to discover that they were there. We’re interested if the yeast is making these important compounds, or possibly enabling the other fungus to make them. We don’t know, but it’s the obvious next question.”

Journal Reference: Basidiomycete yeasts in the cortex of ascomycete macrolichens. 21 July 2016. 10.1126/science.aaf8287

Delivering orange-coloured death to cancer cells

A research effort at Winship Cancer Institute recently identified a substance in orange lichen and rhubarb that has the potential to be used as a new anti-cancer drug. The substance, an orange pigment known as parietin or physcion, slows the growth and can even kill leukemia cells harvested from patients, without obvious toxic effects on human cells, the study authors report.

The work is the result of a project between three laboratories at Whinship, led by Chen, assistant professor of hematology and medical ontology Sumin Kang, PhD and Jun Fan, PhD, assistant professor of radiation oncology. Co-first authors are postdoctoral fellows Ruiting Lin, PhD, and Changliang Shan, PhD, and former graduate student Shannon Elf, PhD, now at Harvard. The results of their work are scheduled for publication in the October 19 edition of Nature Cell Biology.

Parietin is a dominant pigment in Caloplaca lichens. Winship Cancer Institute researchers have shown that it also has anticancer activity.
Image via medicalxpress

The team, led by Jing Chen PhD, was looking for a way to inhibit the metabolic enzyme 6PGD (6-phosphogluconnate dehydrogenase). It’s part of the pentose phosphate pathway, and has a part to play in the synthetisation of aromatic amino acids, nucleotids and fatty acids. In rapid-growing cells, such as those in cancerous tissue, these cellular building blocks are needed in an even greater supply, and 6PGD enzyme activity increased in several types of cancer cells.

But parietin works remarkably well when used against these tissues: not only can the pigment hinder and even kill leukemia cells, but could also inhibit the growth of human cancer cell lines derived from lung and head and neck tumors when grafted into mice.

“This is part of the Warburg effect, the distortion of cancer cells’ metabolism,” says Chen, professor of hematology and medical oncology at Emory University School of Medicine and Winship Cancer Institute. “We found that 6PGD is an important metabolic branch point in several types of cancer cells.”

The laboratories harvested cancer cells from a patient suffering from acute lymphoblastic leukemia. They grew several cultures with these, then tested for and found the dosage required to kill half of the cells in a culture within 48 hours, while leaving healthy blood cells unaffected. One derivative of the pigment, S3, showed even more promising results — when tested on tissue implanted in mice, it cut the growth of a lung cancer cell line by a factor of three in 11 days.

However, even if 6PGB inhibitors do not appear to be toxic to healthy cells in any way, the team advocates that more toxicology research is needed — both to asses potential side effects and to find if certain conditions can make patients’ cells vulnerable to the pigment. While present in some natural food pigments, parietin has not been tested as a drug in humans.



One of the fossils in question - Dickinsonia. Currently, scientists are positive this was a sea-dwelling invertebrate, but recent findings suggest it may actually have been a land-dwelling lichen. (c) Greg Retallack

Controversial study challenges tree of life and claims complex life first originated on land

Professor Gregory Retallack of  University of Oregon has launched a highly controversial claim that stirred the scientific community recently, implying that ancient fossils found in South Australia from Ediacaran period, a geological time that preceded the great Cambrian explosion, were actually living being living on land, not water as “common sense” dictates.

One of the fossils in question - Dickinsonia. Currently, scientists are positive this was a sea-dwelling invertebrate, but recent findings suggest it may actually have been a  land-dwelling lichen. (c) Greg Retallack

One of the fossils in question – Dickinsonia. Currently, scientists are positive this was a sea-dwelling invertebrate, but recent findings suggest it may actually have been a land-dwelling lichen. (c) Greg Retallack

The Ediacaran period ended some 540 million years ago, and during these geological times life on Earth was highly primitive, comprised of individual cells organized in colonies at best.  Ediacaran fossils have been thought of as fossil jellyfish, worms and sea pens, however Retallack argues that he has found evidence that these invertebrates actually originated on land – a claim that has severe implications for our understanding of how life evolved on our planet.

“This discovery has implications for the tree of life, because it removes Ediacaran fossils from the ancestry of animals,” says Retallack, who is originally from Australia.

“These fossils have been a first-class scientific mystery,” he posited. “They are the oldest large multicellular fossils. They lived immediately before the Cambrian evolutionary explosion that gave rise to familiar modern groups of animals.”

Using an assortment of high-tech chemical and microscopic technique, including electron microprobe and scanning electron microscope, Retallack claims he has found soils with fossils that are distinguished by a surface called ‘old elephant skin,’ which is best preserved under covering sandstone beds.

“They show variation in chemistry, variation in grain size, and variation in clay minerals that is quite comparable with a modern desert soil,” he says.

“The key evidence for this new view is that the beds immediately below the cover sandstones in which they are preserved were fossil soils,” Mr. Retallack said. “In other words the fossils were covered by sand in life position at the top of the soils in which they grew. In addition, frost features and chemical composition of the fossil soils are evidence that they grew in cold dry soils, like lichens in tundra today, rather than in tropical marine lagoons.”

Bold claims

Moreover, the geologist claims that many  Ediacaran fossils exhibit features that he believes resemble today’s lichens, than marine invertebrates as the current scientific consensus,  and he also says there is evidence the land they were growing on was sometimes frozen.

This means the Ediacaran fossils represent “an independent evolutionary radiation of life on land that preceded by at least 20 million years the Cambrian evolutionary explosion of animals in the sea.”

Mr. Retallack says that elevated chemical weathering by organisms on land may have been necessary to propel the demand of nutrient elements by Cambrian animals, and based on other fossils from the Cambrian period similar to those studied by him from the Ediacaran, the geologists goes as far to say life on land may have been more complex than life in the sea during the Cambrian explosion. If this is true, then Ediacaran fossils represent an independent branch on the tree of life.

Of course, such a controversial theory was followed by a wave of protest, as scientists called for more substantial evidence to back up the claims.

“I’m sorry, I’m not a creationist. I do not believe that the Cambrian animals popped into existence out of the blue at the beginning of the Cambrian,” Dr Jim Gehling of the South Australian Museum comments on the paper, referring to the fact that if the Ediacaran fossils are  not of marine origin, than the whole boom of life from the Cambrian simply came from “nothing”.

“It’s the right of every scientist to put up controversial hypotheses but you really have to have good evidence if you want to set up a new paradigm,” he says.

Tree of life revamp

Many scientists have no doubts concerning the marine ancestry of the Ediacaran fossils, pointing to wave ripples and other features only formed in marine environments.  Retallack tackles back these comments stating these ripple features could have very well come from subsequent  floods or lakes. Regarding Retallack’s chemical analysis that revealed evidence of fossils soils, Gehling believes these are mere contaminants from more recent weathering events of the ancient rock outcrops that the fossils are found in. Present scientific consensus has that animals only crawled onto land 100 million years after the Ediacaran.

“I find Retallack’s observations dubious, and his arguments poor. That this was published by Nature is beyond my understanding,” wrote Martin Brasier, a paleobiologist at the University of Oxford.

Retallack doesn’t seem bothered at all by the fact that his hypothesis warrants a whole revamp of the current life evolution cycle we call tree of life. On his part, life on land before the Cambrian evolution makes perfect sense as it would have changed the soil chemistry, he says, allowing the release of mineral ions into the soil water.

“Some of this soil water runs off into streams end eventually the ocean,” says Retallack. “That is going to be the engine that drives the Cambrian explosion.”

“What we’re looking at here is the early stages of the ramping up of that process to create the nutrients needed for animal life in the sea.”

Retallack’s findings were published in the journal Nature.