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Carnivorous oyster mushrooms can kill roundworms with “nerve gas in a lollipop”

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Enlarge / Oyster mushrooms (Pleurotus ostreatus) serenely growing on a tree trunk in a forest. But nematodes beware! These oyster mushrooms want to eat you—and they have evolved a novel mechanism for paralyzing and killing you.
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Oyster mushrooms (Pleurotus ostreatus) are a staple of many kinds of cuisine, prized for its mild flavors and a scent vaguely hinting at anise. These cream-colored mushrooms are also one of several types of carnivorous fungi that prey on nematodes (roundworms) in particular. The mushrooms have evolved a novel mechanism for paralyzing and killing its nematode prey: a toxin contained within lollipop-like structures called toxocysts that, when emitted, causes widespread cell death in roundworms within minutes. Scientists have now identified the specific volatile organic compound responsible for this effect, according to a new paper published in the journal Science Advances.

Carnivorous fungi like the oyster mushroom feed on nematodes because these little creatures are plentiful in soil and provide a handy protein source. Different species have evolved various mechanisms for hunting and consuming their prey. For instance, oomycetes are fungus-like organisms that send out “hunter cells” to search for nematodes. Once they find them, they form cysts near the mouth or anus of the roundworms and then inject themselves into the worms to attack the internal organs. Another group of oomycetes uses cells that behave like prey-seeking harpoons, injecting the fungal spores into the worm to seal its fate.

Other fungi produce spores with irritating shapes like stickles or stilettos. The nematodes swallow the spores, which get caught in the esophagus and germinate by puncturing the worm’s gut. There are sticky branch-like structures that act like superglue; death collars that detach when nematodes swim through them, injecting themselves into the worms; and a dozen or so fungal species employ snares that constrict in under a second, squeezing the nematodes to death.

<a href=”https://cdn.arstechnica.net/wp-content/uploads/2023/01/oyster1.jpg” class=”enlarge” data-height=”803″ data-width=”1200″ alt=”Scanning electron microscopy (SEM) image of toxocysts on P. ostreatus hyphae.”><img alt=”Scanning electron microscopy (SEM) image of toxocysts on P. ostreatus hyphae.” src=”https://cdn.arstechnica.net/wp-content/uploads/2023/01/oyster1-640×428.jpg” width=”640″ height=”428″ srcset=”https://cdn.arstechnica.net/wp-content/uploads/2023/01/oyster1.jpg 2x”>
Enlarge / Scanning electron microscopy (SEM) image of toxocysts on P. ostreatus hyphae.
Yi-Yun Lee

The oyster mushroom eschews these physical traps in favor of a chemical mechanism. P. ostreatus is what’s known as a “wood rotter” that targets dead trees, but wood is relatively poor in protein. Its long branching filaments (called hyphae) are the part of the ‘shroom that grows into the rotting wood. Those hyphae are home to the toxocysts. When nematodes encounter the toxocysts, they burst, and the nematodes typically become paralyzed and die within minutes. Once the prey is dead, the hyphae grow into the nematode bodies, dissolving the contents and absorbing the slurry for the nutrients.

In 2020, a team of scientists at Academia Sinica in Taiwan tested all 15 species of P. ostreatus and found that all 15 could produce toxic drops when starved. They also tested 17 species of nematode and found that none could survive exposure to the toxin. Co-author Ching-Han Lee and colleagues suggested that the culprit might be the calcium stored in animal muscles, which, when released in response to nerve signals, causes the muscles to contract. The muscles relax when nerve signals trigger the refilling of the calcium storehouses.

To test the hypothesis, the team conducted experiments where the calcium in the worms was visible, and then tracked the response to exposure to the oyster mushroom toxocysts. They found that the pharynx and head muscles of poisoned nematodes were flooded with calcium and said calcium did not go away, leading to widespread nerve and muscle cell death. They suggested that the toxin triggers the initial calcium response, but then jams the mechanism by which the nematodes refurbish their calcium supply.

A mitochondrial calcium wave propagating throughout the hypodermis tissue after contacting P. ostreatus.Credit: Ching-Han Lee

But Lee et al. could not identify the specific toxins responsible for the effect, though they did note that the oyster mushroom’s chemical mechanism was distinct from the nematicides currently used to control nematode populations. For the new study, Lee and co-authors used gas chromatography-mass spectrometry to do just that. The first version of the experiment tested a vial sample containing just the culture medium and glass beads. A second version tested a vial sample containing P. ostreatus that had been cultured for two to three weeks. The third version was a combination of the first two, testing a vial sample that contained both cultured P. ostreatus and glass beads.

The culprit: a volatile ketone called 3-octanone, one of several naturally occurring volatile organic compounds (VOCs) that fungi use for communication. It seems 3-octanone also serves as a potent nematode-killing mechanism. Exposing four species of nematode to 3-octanone triggered the telltale massive (and fatal) influx of calcium ions into nerve and muscle cells. The dosage is critical, per the authors. Low dosages are a repellant to slugs and snails, but high dosages are fatal. The same is true for nematodes. A high concentration of more than 50 percent of 3-octanone is required to trigger the rapid paralysis and widespread cell death. The team also induced thousands of random genetic mutations in the fungus. Those mutants that didn’t develop toxocysts on their hyphae were no longer toxic to the nematode Caenorhabditis elegans.

As for why oyster mushrooms evolved such an unusual mechanism for killing nematodes, the authors suggest that it’s because dying or rotting trees are particularly poor in nitrogen, and this mechanism is a good way for the mushrooms to make up for that deficiency. The toxocysts might even serve a defensive purpose. Specific species of nematode can pierce the fungal hyphae to suck out the cytoplasm, so having toxocysts that emit poison gas on the hyphae could protect the fungus from such predators.

DOI: Science Advances, 2023. 10.1126/sciadv.ade4809  (About DOIs).

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Las Vegas Aces Rookie Kate Martin Suffers Ankle Injury in Game Against Chicago Sky

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Las Vegas Aces rookie Kate Martin had to be helped off the floor and taken to the locker room after suffering an apparent ankle injury in the first quarter of Tuesday night’s game against the Chicago Sky.

Late in the first quarter, Martin was pushing the ball up the court when she appeared to twist her ankle and lost her balance. The rookie was in serious pain, lying on the floor before eventually being helped off. Her entire team came out in support, and although she managed to put some pressure on the leg, she was taken to the locker room for further evaluation.

Martin returned to the team’s bench late in the second quarter but was ruled out for the remainder of the game.

“Kate Martin is awesome. Kate Martin picks up things so quickly, she’s an amazing sponge,” Aces guard Kelsey Plum said of the rookie during the preseason. “I think (coach) Becky (Hammon) nicknamed her Kate ‘Money’ Martin. I think that’s gonna stick. And when I say ‘money,’ it’s not just about scoring and stuff, she’s just in the right place at the right time. She just makes people better. And that’s what Becky values, that’s what our coaching staff values and that’s why she’s gonna be a great asset to our team.”

Las Vegas selected Martin in the second round of the 2024 WNBA Draft. She was coming off the best season of her collegiate career at Iowa, where she averaged 13.1 points, 6.8 rebounds, and 2.3 assists per game during the 2023-24 campaign. Martin’s integration into the Aces organization has been seamless, with her quickly earning the respect and admiration of her teammates and coaches.

The team and fans alike are hoping for a speedy recovery for Martin, whose contributions have been vital to the Aces’ performance this season.

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Asteroid Apophis will visit Earth in 2029, and this European satellite will be along for the ride

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The European Space Agency is fast-tracking a new mission called Ramses, which will fly to near-Earth asteroid 99942 Apophis and join the space rock in 2029 when it comes very close to our planet — closer even than the region where geosynchronous satellites sit.

Ramses is short for Rapid Apophis Mission for Space Safety and, as its name suggests, is the next phase in humanity’s efforts to learn more about near-Earth asteroids (NEOs) and how we might deflect them should one ever be discovered on a collision course with planet Earth.

In order to launch in time to rendezvous with Apophis in February 2029, scientists at the European Space Agency have been given permission to start planning Ramses even before the multinational space agency officially adopts the mission. The sanctioning and appropriation of funding for the Ramses mission will hopefully take place at ESA’s Ministerial Council meeting (involving representatives from each of ESA’s member states) in November of 2025. To arrive at Apophis in February 2029, launch would have to take place in April 2028, the agency says.

This is a big deal because large asteroids don’t come this close to Earth very often. It is thus scientifically precious that, on April 13, 2029, Apophis will pass within 19,794 miles (31,860 kilometers) of Earth. For comparison, geosynchronous orbit is 22,236 miles (35,786 km) above Earth’s surface. Such close fly-bys by asteroids hundreds of meters across (Apophis is about 1,230 feet, or 375 meters, across) only occur on average once every 5,000 to 10,000 years. Miss this one, and we’ve got a long time to wait for the next.

When Apophis was discovered in 2004, it was for a short time the most dangerous asteroid known, being classified as having the potential to impact with Earth possibly in 2029, 2036, or 2068. Should an asteroid of its size strike Earth, it could gouge out a crater several kilometers across and devastate a country with shock waves, flash heating and earth tremors. If it crashed down in the ocean, it could send a towering tsunami to devastate coastlines in multiple countries.

Over time, as our knowledge of Apophis’ orbit became more refined, however, the risk of impact  greatly went down. Radar observations of the asteroid in March of 2021 reduced the uncertainty in Apophis’ orbit from hundreds of kilometers to just a few kilometers, finally removing any lingering worries about an impact — at least for the next 100 years. (Beyond 100 years, asteroid orbits can become too unpredictable to plot with any accuracy, but there’s currently no suggestion that an impact will occur after 100 years.) So, Earth is expected to be perfectly safe in 2029 when Apophis comes through. Still, scientists want to see how Apophis responds by coming so close to Earth and entering our planet’s gravitational field.

“There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the solar system to study them and perform experiments ourselves to interact with their surface,” said Patrick Michel, who is the Director of Research at CNRS at Observatoire de la Côte d’Azur in Nice, France, in a statement. “Nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis is stretched and squeezed by strong tidal forces that may trigger landslides and other disturbances and reveal new material from beneath the surface.”

The Goldstone radar’s imagery of asteroid 99942 Apophis as it made its closest approach to Earth, in March 2021. (Image credit: NASA/JPL–Caltech/NSF/AUI/GBO)

By arriving at Apophis before the asteroid’s close encounter with Earth, and sticking with it throughout the flyby and beyond, Ramses will be in prime position to conduct before-and-after surveys to see how Apophis reacts to Earth. By looking for disturbances Earth’s gravitational tidal forces trigger on the asteroid’s surface, Ramses will be able to learn about Apophis’ internal structure, density, porosity and composition, all of which are characteristics that we would need to first understand before considering how best to deflect a similar asteroid were one ever found to be on a collision course with our world.

Besides assisting in protecting Earth, learning about Apophis will give scientists further insights into how similar asteroids formed in the early solar system, and, in the process, how  planets (including Earth) formed out of the same material.

One way we already know Earth will affect Apophis is by changing its orbit. Currently, Apophis is categorized as an Aten-type asteroid, which is what we call the class of near-Earth objects that have a shorter orbit around the sun than Earth does. Apophis currently gets as far as 0.92 astronomical units (137.6 million km, or 85.5 million miles) from the sun. However, our planet will give Apophis a gravitational nudge that will enlarge its orbit to 1.1 astronomical units (164.6 million km, or 102 million miles), such that its orbital period becomes longer than Earth’s.

It will then be classed as an Apollo-type asteroid.

Ramses won’t be alone in tracking Apophis. NASA has repurposed their OSIRIS-REx mission, which returned a sample from another near-Earth asteroid, 101955 Bennu, in 2023. However, the spacecraft, renamed OSIRIS-APEX (Apophis Explorer), won’t arrive at the asteroid until April 23, 2029, ten days after the close encounter with Earth. OSIRIS-APEX will initially perform a flyby of Apophis at a distance of about 2,500 miles (4,000 km) from the object, then return in June that year to settle into orbit around Apophis for an 18-month mission.

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Furthermore, the European Space Agency still plans on launching its Hera spacecraft in October 2024 to follow-up on the DART mission to the double asteroid Didymos and Dimorphos. DART impacted the latter in a test of kinetic impactor capabilities for potentially changing a hazardous asteroid’s orbit around our planet. Hera will survey the binary asteroid system and observe the crater made by DART’s sacrifice to gain a better understanding of Dimorphos’ structure and composition post-impact, so that we can place the results in context.

The more near-Earth asteroids like Dimorphos and Apophis that we study, the greater that context becomes. Perhaps, one day, the understanding that we have gained from these missions will indeed save our planet.

 

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McMaster Astronomy grad student takes a star turn in Killarney Provincial Park

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Astronomy PhD candidate Veronika Dornan served as the astronomer in residence at Killarney Provincial Park. She’ll be back again in October when the nights are longer (and bug free). Dornan has delivered dozens of talks and shows at the W.J. McCallion Planetarium and in the community. (Photos by Veronika Dornan)

Veronika Dornan followed up the April 8 total solar eclipse with another awe-inspiring celestial moment.

This time, the astronomy PhD candidate wasn’t cheering alongside thousands of people at McMaster — she was alone with a telescope in the heart of Killarney Provincial Park just before midnight.

Dornan had the park’s telescope pointed at one of the hundreds of globular star clusters that make up the Milky Way. She was seeing light from thousands of stars that had travelled more than 10,000 years to reach the Earth.

This time there was no cheering: All she could say was a quiet “wow”.

Dornan drove five hours north to spend a week at Killarney Park as the astronomer in residence. part of an outreach program run by the park in collaboration with the Allan I. Carswell Observatory at York University.

Dornan applied because the program combines her two favourite things — astronomy and the great outdoors. While she’s a lifelong camper, hiker and canoeist, it was her first trip to Killarney.

Bruce Waters, who’s taught astronomy to the public since 1981 and co-founded Stars over Killarney, warned Dornan that once she went to the park, she wouldn’t want to go anywhere else.

The park lived up to the hype. Everywhere she looked was like a painting, something “a certain Group of Seven had already thought many times over.”

The dome telescopes at Killarney Provincial Park.

She spent her days hiking the Granite Ridge, Crack and Chikanishing trails and kayaking on George Lake.  At night, she went stargazing with campers — or at least tried to. The weather didn’t cooperate most evenings — instead of looking through the park’s two domed telescopes, Dornan improvised and gave talks in the amphitheatre beneath cloudy skies.

Dornan has delivered dozens of talks over the years in McMaster’s W.J. McCallion Planetarium and out in the community, but “it’s a bit more complicated when you’re talking about the stars while at the same time fighting for your life against swarms of bugs.”

When the campers called it a night and the clouds parted, Dornan spent hours observing the stars. “I seriously messed up my sleep schedule.”

She also gave astrophotography a try during her residency, capturing images of the Ring Nebula and the Great Hercules Cluster.

A star cluster image by Veronika Dornan

“People assume astronomers take their own photos. I needed quite a lot of guidance for how to take the images. It took a while to fiddle with the image properties, but I got my images.”

Dornan’s been invited back for another week-long residency in bug-free October, when longer nights offer more opportunities to explore and photograph the final frontier.

She’s aiming to defend her PhD thesis early next summer, then build a career that continues to combine research and outreach.

“Research leads to new discoveries which gives you exciting things to talk about. And if you’re not connecting with the public then what’s the point of doing research?”

 

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