Posts Tagged ‘fungi’

by Annie Greene

After the Chimney Tops 2 Wildfire charred 11,000 acres of the Great Smoky Mountains National Park along the North Carolina–Tennessee state line in November 2016, rangers closed affected trails to visitors. Mycologists Andy N. Miller and Karen Hughes and their teams were an exception. Toting hard hats and sample collection kits, these scientists jumped at the opportunity to track down their research subjects: pyrophilous (“fire-loving”) fungi, which produce mushrooms prolifically after forest fires and then disappear as the forest recovers.

The severely burned areas of the Smokies were almost completely lifeless two months after the blaze, when the group first ventured into the affected zone. “The level of destruction was incredible,” recounts Hughes, a researcher at the University of Tennessee, Knoxville, in an email to The Scientist. “Everything I touched left black carbon on my hands. It was incredibly quiet.” Miller, who is based at the University of Illinois Urbana-Champaign, also noted a surreal lack of activity. “There’s nothing running around, no birds singing,” he says. To him, the site smelled “like a house had burned up.” When the researchers returned to their collection sites a few months later, however, their mushrooms of interest had risen from the ashes. Miller noticed that when these fungi surface, they do so en masse: “They’re less than a millimeter in diameter, but there’s a lot of them, and once you train your eyes, they’re just all over the place.”

The researchers were interested in documenting which species of pyrophilous fungi are present in the Smokies. They also wanted to test a theory about where the fungi go during the long periods between forest fires. Some fire-loving fungi are known to lie dormant in the dirt as spores or other heat-tolerant structures until post-fire soil conditions trigger growth and reproduction. Other species exist between burns in a vegetative state, aiding decomposition of dead organisms or interacting with tree roots. But many fire-loving fungi don’t fit into any of these categories. A new proposal, known as the body snatchers hypothesis, posits that some pyrophilous fungi hide out inside plants or lichens in between fires, nestling among host cells in a so-called endophytic or endolichenic state.

To test the hypothesis, the researchers traveled to the burn site every few months for more than a year to sample the soil, as well as the mosses and lichens that sprang up while the forest recovered. They also gathered specimens from unburned areas of the park for comparison. In May 2018, members of Miller’s lab began analyzing the samples they’d collected. DNA sequencing results identified a total of 22 pyrophilous fungal species in the Smokies. Of these, three species were present only in the soil, while the remaining 19 were found inside plant samples from burned and unburned areas, either exclusively or in addition to being found in the soil. In line with the body snatchers hypothesis, “almost all of our pyrophilous fungi were found as endophytes,” Miller says.

Mosses and lichens often live in difficult-to-reach places such as rock crevices and may be hardy enough to withstand minor flames, so fungi living inside these hosts could theoretically survive a low-intensity wildfire. But it’s still unclear how all of these organisms might persist through a moderate or severe burn, and how a fire-loving fungus would escape its host to recolonize a charred forest. Hughes has a hypothesis based on her observations at the burn site: “After the fire, I saw numerous tiny lichen fragments on the burned soil, as if they had been lofted into the air while trees were burning and settled on the ground after the fire,” she says. These burned plant fragments may inoculate the soil with the fungi they harbor, giving the fire-loving fungi a way into the dirt.

This is a feasible way for both a pyrophilous fungus and its host to rebound after a fire and maintain their relationship, according to Keith Clay, who studies plant-fungus interactions at Tulane University and was not involved with this study. “If [a moss fragment] lands in a good place, it can regenerate the whole plant,” says Clay. “If the endophyte is in that fragment, presumably it can just colonize these newly grown plants as well from the get-go.” Post-fire fungi may also acquire new hosts after a burn, Miller notes. One mushroom can produce millions of airborne spores that likely land on nearby mosses and lichens, germinate, and invade the tissues of these new hosts, he says.

To check whether their findings might apply to other forests, Miller and Hughes analyzed moss and lichen samples from other sites around the US. A handful of the fire-loving fungi identified in the Smokies were also present as endophytes in Indiana and Alaska. That result was surprising because “there was really no evidence that a fire had occurred in the last few years in those areas,” Miller says. “What are they doing there if they’re not waiting for a fire to come along?”

One possibility is that, while body snatching between fires, pyrophilous fungi use their plant hosts as nutrient sources, says Clay. He notes that many plants and fungi have mutualistic endophytic relationships, where the plant typically provides the fungus with “a home where they can live and sugars, carbon, from photosynthesis.” In return, the fungus often produces alkaloids that benefit the host. Yet for the pyrophilous fungi examined in this study, Clay says, “what they offer the plant is not clear.” Sydney Glassman, a microbial ecologist at the University of California, Riverside, who was not involved with the study, notes that in vitro assays using carbon isotopes could help uncover these trade-offs by revealing “nutrient transfer between the plants and the fungus.”

Miller and his team plan to examine the details of fungus-host interactions by recreating body snatching in the lab and conducting long-term field studies, he notes. After all, many forests where pyrophilous fungi live go for decades without fire, he says. “So how is that relationship maintained?”

By Jennifer Frazer

In addition to irritatingly lodging themselves everywhere from shower grout to the Russian space station Mir, fungi that live inside rocks in Antarctica have managed to survive a year and half in low-Earth orbit under punishing Mars-like conditions, scientists recently reported in the journal Astrobiology. A few of them even managed to cap their year in Mars-like space by reproducing.

Why were they subjected to such an ordeal? Scientists have concluded over the past decade that Mars (which like Earth is about four and a half billion years old) supported water for long periods during its first billion years, and they wonder if life that may have evolved during that time may remain on the planet in fossilized or even fresh condition. The climate back then was more temperate than today, featuring a thicker atmosphere and a more forgiving and moist climate.

But how do you search for that life? Using life that exists in what they believe is this planet’s closest analogue, a team of scientists from Europe and the United States hoped to identify the kind of biosignatures that might prove useful in such a search, while also seeing if the Earthly life forms might be capable of withstanding current Mars-like conditions.

Which is to say, not nice.

The temperature on Mars fluctuates wildly on a daily basis. The Mars Science Laboratory rover has measured daily swings of up to 80°C (that’s 144°F), veering from -70°C(-94°F) at night to 10°C(50°F) at Martian high noon. If you can survive that, you also have to get past the super-intense ultraviolet radiation, an atmosphere of 95% carbon dioxide (the effect of which on humans was vividly illustrated at the end of Total Recall), a pressure of 600 to 900 Pascals (Earth: 101,325 Pascals), and cosmic radiation at a dose of about .2mGy/day (Earth: .001 mGy/day). I don’t know about you, but Mars is not my first vacation choice.

And it’s probably not Cryomyces antarcticus’s either, in spite of the extreme place it calls home. Cryomyces antarcticus and its relative Cryomyces minteri – the two fungi tested independently in this study — are members of a group called black fungi or black yeast for their heavily pigmented hulls that allow them to withstand a wide variety environmental stresses. Members of the group somewhat notoriously turned up a few years ago in a study that found two species of the group commonly live inside dishwashers in people’s homes (they were opportunistic human pathogns, but most humans are immune to them). But most of these fungi live quietly in the most extreme environments on earth.

The particular black fungi used in this experiment, generally considered the toughest on the planet, live in tiny tunnels of their own creation inside Antarctic rocks. This is apparently the only place they can grow without being annihilated by the crushing climate and blistering ultraviolet radiation of Antarctica. Antarctica also happens to be the place on Earth most similar – although still not particularly similar, as you have seen — to our friendly neighborhood Red Planet. This endurance has made both black fungi and their neighbors the lichens popular test pilots for Mars-like conditions on the international space station.

For example, lichen-forming fungi that create the common and beautiful orange Xanthoria elegans and also Acarospora made the same trip to the ISS previously, in a European module of the International Space Station called EXPOSE-E. Both survived the experience, and Acarospora even managed to reproduce.

But this seems to be the first time a non-lichen forming fungus has received the ISS treatment.

These particular two fungi – Cryomyces antarcticus and Cryomyces minteri – were collected from the McMurdo Dry Valleys of Antarctica in Southern Victoria Land, supposedly the most Mars-like place on Earth. They were isolated from dry sandstone onto a plate of fungus food called malt extract agar. This gelatinous disc was then dried along with the fungus living on it inside a dessicator, and sent into space like that.

Each colony was about 1mm in diameter, and each yeast cell in it was 10 micrometers in size. Like most black yeast/fungi, they have a dark outer wall.

The scientists also tested an entire community of “cryptoendolithic” organisms – those that live secretly inside rocks, including not just fungi but also rock-dwelling blue-green algae – by testing whole fragments of rocks collected on Battleship Promontory in Southern Victoria Land, Antarctica. The various organisms live in bands of varying color and depth within 1 centimeter of the rock surface.

The fungi were launched into space in February 2008 and returned to Earth on September 12, 2009. During that time they were placed in a bath of gasses as similar as possible to the atmosphere of Mars and exposed to simulated full Martian UV radiation, one-thousandth Martian UV, or kept in the dark. They also endured the cosmic background radiation of space and temperature swings between -21.7°C and 42.9°C – much warmer than Mars, but the best that could be done. Control samples remained in the dark on Earth.

Once back on Earth, the colonies and rock samples were rehydrated. Their appearance had not changed during their voyage. They were then tested for viability by diluting them in water and plating the resulting solution to see how many new colonies formed. They also estimated the percentage of cells with undamaged cell membranes by using a chemical that can only penetrate damaged cell membranes.

The scientists found that the black yeast’s ability to form new colonies was severely impaired by its time on “Mars”, but it was not zero. When kept in the dark on the ISS, about 1.5% of C. antarcticus was able to form colonies post-exposure, while only .08% of C. minteri could. Surprisingly, those exposed to .1% of Mars UV did better, with 4-5 times more surviving: just over 8% for C. antarcticus and 2% for C. minteri. Perhaps the weak radiation stimulated mutations or stress-response proteins that might have helped the fungi somehow.

With the full force of Martian radiation, the survival rates were about the same as for those samples kept in the dark, which is to say, nearly nil. By comparison, about 46% of control C. antarcticus samples kept in the dark back on Earth yielded colony forming units, while only about 17% of C. minteri did. Not super high rates, but still much higher than their space-faring comrades.

On the other hand, the percentage of cells with intact cell membranes was apparently much higher than the number that could reproduce. 65% of C. antarcticus cells remained intact regardless of UV exposure, while C. minteri’s survival rates fluctuated between 18 and 50%, again doing better with UV exposure than in the dark. Colonized rock communities yielded the highest percentage of intact cells of any samples when kept in the dark – around 75%, but some of the lowest when exposed to solar UV, with just 10-18 % surviving intact.

What explains this apparent survival discrepancy between being alive and being able to reproduce? It may be that the reproductive apparati of the fungi are more sensitive to cosmic radiation than their cell membranes and walls, the authors suggest.

The authors’ results also suggest to them that DNA is the biomolecule of choice to use to search for life on Mars, as it, like the cell membranes, survived largely intact even in cells that could no longer reproduce.

Although Mars-based life may not use DNA genetic material, then again, it just might. It certainly seems to have worked well for us here on Earth.

Even though few of the fungi exposed to Mars-like conditions survived well enough to reproduce, in all cases, at least a fraction did. Perhaps that is the material thing. A similar previous experiment showed one green alga, Stichococcus, and one fungus, Acarospora were able to reproduce after a very similar trip on the space station. Another experiment with the bacterium Bacillus subtilis found that up to 20% of their spores were able to germinate and grow after Mars-like exposure. Theoretically, it only takes one or two to hang on and adapt to these conditions to found a whole lineage of Mars-tolerant life (the major reason, by the way, for NASA’s Planetary Protection Program).

On the other hand, some have suggested that long-term survival of Earthly life is impossible on Mars. Given the extremely low reproductive ability after just 1.5 years, this study did nothing to undermine that idea either.

But all of our studies have tested life that evolved on Earth. What about life that evolved on Mars? There’s just no telling how similar or dissimilar such creatures — supposing they exist or ever existed – might be.