In our last blog, we published excursion notes by two team members, side by side, creating an experimental duet of ideas and impressions. This week, we’re taking a similar approach, only the subject is lichens. Two authors, two points of view, side by side.
The Super-organism
by Doug Pope
To appreciate the strangeness of lichens, we need to compare them to humans. As most people know, lichens are super-organisms, with at least 3 different species fusing and reproducing together. Could a human baby have more than two biological parents? According to the Associated Press, British doctors have created the first test tube human babies using eggs from two mothers and the sperm from a single father. (AP, May 10, 2023) As reporter Maria Cheng notes : “Britain’s fertility regulator on Wednesday confirmed the births of the U.K.’s first babies created using an experimental technique combining DNA from three people, an effort to prevent the children from inheriting rare genetic diseases.”
Have we entered some strange realm of science fiction here? No, it’s a true story. Combining three sets of human DNA is rare now, but as we try to prevent birth defects it may become more and more common.
Now let’s consider the case of lichen. Also three sets of DNA. But rather than having donors all of the same species, here we have three separate species. Two fungus, one algae. It would be like sprouting a baby from an oak tree, a giraffe and a zebra. Yeast making love to a mushroom making love to seaweed. No wonder it took scientists 150 years to figure it out!
However, when it comes to mixing and swapping DNA, bacteria are the true genetic marvels. It took the world’s greatest microbiologist, Carl Woese a lifetime to prove it and to give the phenomena a name: horizontal gene transfer. Bacteria swim in crowded pools and when they touch or bump another body, they may add or subtract a gene. They reproduce asexually, but their genes are always changing. This allows them to be the most adaptable and biodiverse creatures on the planet. Also the oldest and longest surviving.
Can people transfer genes horizontally, that is, without sex? Yes, but it’s not as much fun. Seriously, how does a baby acquire its microbiome? By passing through the birth canal, through breast-feeding and nurture—human touch and diet, the child will pick up more bacterial DNA than the human DNA he or she was born with. It’s horizontal gene transfer, human style.
Scientists have only begum to look for these extra-species gene transfers in other organisms. We know trees and wasps combine genes to form galls. We know that ocean coral has properties and DNA of both plants and animals. Algae infiltrate the eggs of salamanders, providing extra energy (momentarily turning an unborn amphibian into a plant) and giving the eggs a greenish colour. Fungi infiltrate cells in the roots of trees. Nitrogen-fixing pea plants form nodules in their roots to accommodate rhizobia bacteria.
In 1991, American microbiologist Lynn Margulis coined the word holobiont to describe an assemblage of a host and the many other species living in or around it, which together form a discrete ecological unit. A holobiont relationship exists when the host and its collective microbial community perform functions that cannot be accomplished by the partners separately.
Holobionts are sometimes referred to as metaorganisms. By the above definition, human beings are clearly holobionts, as we depend on mitochondria for energy and on bacteria to digest our food, to assist the immune system, to control our moods and to move iron and other essential elements into our blood. We could not exist without the microbiota living inside us.
As I look at the strangeness of lichens, exemplars of the mutual cooperation of unlike things, I think how this is not the exception in nature, but closer to the rule.
A Reexamination of Assumptions: Looking at Lichens
by Tegan McMahon
I know that we have probably all seen lichen before, but how many do you think have actually looked? Teachers have been using lichens to teach symbiotic relationships for years, but it turns out that they didn’t even know how many organisms are involved in the creation of lichens…
The first person who realized that lichen was created by a symbiotic relationship between at least two different organisms was Simon Schwendener, a Swiss botanist who suggested over 150 years ago, that the fungi get nutrients from the algae and/or cyanobacteria in return from the protection and structure that the fungi provides. Since then everyone seemed to take it as fact that the relationship only happens between one fungus and one algae and/or cyanobacteria in any given lichen.
Recently researchers have been looking at lichens with fresh eyes after they realized that many of our fundamental assumptions about lichens are wrong. For example, multiple studies have found that lichens commonly have up to three different types of fungi! Though research is still being done to figure out what each partner contributes to the relationship.
Most of these studies were undertaken by Toby Spribille, as well as a multitude of individuals that helped during the different studies. The first of his studies focusing on this topic happened in 2016, he was studying two lichens that were supposedly genetically identical but were different colours and while one had been eaten for centuries the other was poisonous, the Brown Wila Horsehair and Yellow Tortured Horsehair lichen; he was sure that the previous study had been too coarse and had missed something in the genetic sequence, so he ran it again. To his shock, he found that their results were correct, so he started to look at some of the other results he had written off as contamination. He found that both of the lichens constantly had a third DNA sequence, a type of yeast from the basidiomycetes group, but that the poisonous type of lichen had it in much higher quantities. Once he found this second type of fungi in both these lichens he started looking at others and found that almost all structurally complex lichens had at least a second type of fungi and that some had three.
Another assumption about lichens that is being challenged right now, is the assumption that the fungi get all of its sugar from their algae partner. It was expected that the relationship would resemble the symbiotic relationships between fungi and plants where the fungi lose the enzymes that allow them to break down raw carbohydrates. However, it seems that both the fungi and the algae can supply sugars, though there are some theories that one of them supplies sugar when the lichen is active while the other supplies it when the lichen is dormant due to lack of water.
This was another study spearheaded by Toby Spribille where he looked at the DNA sequence as well as other evidence, such as the existence of optional lichens (some fungi have the ability to switch between a solitary lifestyle as a fungi, and being a lichen if they find the right algae partners). He likened the existence of these enzymes in the fungal partners to being similar to seeing butcher equipment in the kitchen of your vegetarian friend, where it doesn’t necessarily mean that they are eating meat but it does beg some questions.
Lichens have been long known to be one of the dominating pioneer species in primary succession. In areas where only rock is exposed, lichens manage to gain a foothold and start producing soil and organic materials. They have many different methods of doing this: by breaking down the rocks into fine particles with threadlike growths (similar to roots but they seem to have no functions other than anchoring the lichen to where it is growing) that expand and contract up to 300% depending on the level of water available to the lichen. They also break down the rocks using chemical commands such as Oxalic acid, which is known to be one of the most effective agents for rock degradation. Lichens also trap airborne particles and accumulate nutrients that decompose once the lichen dies. Thus lichens are very important in areas such as the tundra and in areas after a disaster such as a volcano eruption.
Lichens, though until recently long overlooked when it comes to being used by humans, used to be used by many cultures all over the world. Lichens were used as a food source in winter by many peoples when very little else was available as they seem to be rich in nutrition. However, they were mostly eaten in emergency situations as they are not very appealing…
Lichens have also been used to make dyes by many different cultures, for example, the Scots often used lichens to dye their kilts. Lichens can make a wide range of brilliant colours, from oranges and yellows to blues and pinks as well as bright purple dyes. The purple dye is notable as there are very few natural methods of creating a purple dye and at certain points in time this colour was so prized its use was restricted to royalty.
More recently lichens have been used as low-tech air quality monitors. As lichens have little to no roots they need to acquire almost all their nutrients and water from the air. Lichens are very sensitive to nitrogen and sulphur dioxide concentrations in the atmosphere, though different species have different levels of tolerance to the pollutants so depending on what lichens are surviving in an area one can tell the level of pollution. Lichens also absorb heavy metals and toxic trace elements which is a problem as animals such as caribou and reindeer graze on the lichen during the winter which can cause the meat to be too radioactive for human consumption during certain seasons.
Lichens are also being studied as a potential source of medicines as they have unique chemical compounds that might be useful as antibacterial, antimicrobial, or anticancer drugs!