Natures wonders: lichens triple symbiosis (Introduction)

by David Turell , Monday, July 25, 2016, 15:30 (3041 days ago) @ David Turell

Lichens are fungus/algae combinations which break down rock, making soil, vital for development of a habitable Earth. Now it is learned they can have three partners:-http://www.theatlantic.com/science/archive/2016/07/how-a-guy-from-a-montana-trailer-park-upturned-150-years-of-biology/491702/-"Lichens have an important place in biology. In the 1860s, scientists thought that they were plants. But in 1868, a Swiss botanist named Simon Schwendener revealed that they're composite organisms, consisting of fungi that live in partnership with microscopic algae. This “dual hypothesis” was met with indignation: it went against the impetus to put living things in clear and discrete buckets. The backlash only collapsed when Schwendener and others, with good microscopes and careful hands, managed to tease the two partners apart.-***-"In the 150 years since Schwendener, biologists have tried in vain to grow lichens in laboratories. Whenever they artificially united the fungus and the alga, the two partners would never fully recreate their natural structures. It was as if something was missing—and Spribille might have discovered it.-"He has shown that largest and most species-rich group of lichens are not alliances between two organisms, as every scientist since Schwendener has claimed. Instead, they're alliances between three. All this time, a second type of fungus has been hiding in plain view. -***-"Throughout his career, Spribille had collected some 45,000 samples of lichens. He began screening these, from many different lineages and continents. And in almost all the macrolichens—the world's most species-rich group—he found the genes of basidiomycete fungi. They were everywhere. Now, he needed to see them with his own eyes.-"Down a microscope, a lichen looks like a loaf of ciabatta: it has a stiff, dense crust surrounding a spongy, loose interior. The alga is embedded in the thick crust. The familiar ascomycete fungus is there too, but it branches inwards, creating the spongy interior. And the basidiomycetes? They're in the outermost part of the crust, surrounding the other two partners. “They're everywhere in that outer layer,” says Spribille.-"Despite their seemingly obvious location, it took around five years to find them. They're embedded in a matrix of sugars, as if someone had plastered over them. To see them, Spribille bought laundry detergent from Wal-Mart and used it to very carefully strip that matrix away.-"And even when the basidiomycetes were exposed, they weren't easy to identify. They look exactly like a cross-section from one of the ascomycete branches. Unless you know what you're looking for, there's no reason why you'd think there are two fungi there, rather than one—which is why no one realised for 150 years. Spribille only worked out what was happening by labeling each of the three partners with different fluorescent molecules, which glowed red, green, and blue respectively. Only then did the trinity become clear.-“'The findings overthrow the two-organism paradigm,” says Sarah Watkinson from the University of Oxford. “Textbook definitions of lichens may have to be revised.”-"It makes lichens all the more remarkable,” adds Nick Talbot from the University of Exeter. “We now see that they require two different kinds of fungi and an algal species. If the right combination meet together on a rock or twig, then a lichen will form, and this will result in the large and complex plant-like organisms that we see on trees and rocks very commonly. The mechanism by which this symbiotic association occurs is completely unknown and remains a real mystery.”-"Based on the locations of the two fungi, it's possible that the basidiomycete influences the growth of the other fungus, inducing it to create the lichen's stiff crust. Perhaps by using all three partners, lichenologists will finally be able to grow these organisms in the lab."-Comment: An amazing advance. Lichens are absolutely necessary for life on Earth, which started as a totally rocky planet, without soil. Take a hike along a rocky trial and you will see them as blotchy colored matches on rocks, like lava or granite. How did three separate organisms join together to produce this result, chance or purposeful by God?