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Airborne antibiotic resistance, farms supporting biodiversity and how black holes eat


Time for this week's science roundup from our friends at NPR's Short Wave podcast, Aaron Scott and Regina Barber. Good to have you both here.



SHAPIRO: You've brought us three science stories that caught your eye this week. What have you got for us this time?

SCOTT: We have drug-resistant germs catching a ride on air pollution particles...

BARBER: The mysterious eating habits of black holes...

SCOTT: And how farms can support biodiversity.

SHAPIRO: All right. Let's start with the dark stuff. As if drug-resistant germs were not good enough, they're riding on air pollution?

BARBER: Yeah. But not any germs - we're talking about superbugs, like bacteria resistant to antibiotics. A lot of these come from places like farms, hospitals, sewage treatment facilities, and over a million people died globally in 2019 from drug-resistant bacterial infections. And it's estimated this problem is just going to get worse, decades to come.

SCOTT: Yeah. And we've long known that these bacteria lurk in the soil and in waterways, but what is new is that it turns out air pollution could also be a major contributing factor to the spread of these antibiotic-resistant germs. Our colleague, Gabriel Spitzer, just wrote about a recent study in the journal Lancet Planetary Health that found that, globally, the rates of particulate air pollution and antibiotic-resistant infection are closely linked. They're both on the rise overall, and low-income regions of the world tend to face the highest rates of both of them.

SHAPIRO: That sounds really unpleasant, but do we know that one causes the other, or is there a chance that antimicrobial resistance is just more common in the same kinds of places that have a lot of air pollution?

BARBER: Right. We should say that this study does not establish a causal relationship between air pollution and antibiotic resistance or examine the actual biological mechanism that might be at play here. But researchers did adjust for factors that could affect the rate of antibiotic resistance, like socioeconomic status, health expenditures and education, and it still does show this really strong and interesting association between the two.

SHAPIRO: So how does this actually work? I'm imagining a drug-resistant bacteria riding sidesaddle on a air pollution particle. Like, what - paint a picture for me.

SCOTT: It's actually a good image, Ari. One of the researchers NPR talked to didn't use the equestrian metaphor. They actually went with islands - that these are like islands that the bacteria can hitch a ride on and can actually set up little communities that are kind of floating around on the particulates through the air.

BARBER: And what we don't know much about is whether these little floating islands can actually spread antibiotic-resistant infections to people.

SHAPIRO: So we're not yet ready to say that air pollution does spread antibiotic resistance. Sounds like there's more work to be done here.

SCOTT: Yes, yes. There's more study that needs to be done. But the thing is, if it turns out there is a link, this could give countries more incentive to reduce air pollution, given that we already know that pollution itself can damage your health.

SHAPIRO: All right.

From the microscopic to the astronomical, tell me about the feeding habits of black holes, please.

BARBER: Yeah. So when people think about black holes, they think of, like, these stellar vacuum cleaners that suck up everything. But in reality, they only suck up stuff that are right next to it, like dust and gas from, like, a nearby star. And now a team of scientists led by astronomers in China has observed something that has only been theorized or seen in computational models - a black hole where that dust and gas is no longer getting sucked in. It's halted, and the gravity from the black hole is no longer winning. This is all detailed in a paper that was published last week in Science.

SHAPIRO: Are there pictures? What does this actually look like?

BARBER: There isn't pictures of this black hole.

SCOTT: But what you want to picture is, you know, the black hole is sucking that dust and gas from the nearby star towards its center, and that creates a disk around the black hole. So if you want to imagine something, Ari, it's imagining a bright donut in space with a black hole at the center.

SHAPIRO: It's like "Everything Everywhere All At Once" - the everything bagel.

BARBER: Yes. Yes.

SCOTT: Exactly.

BARBER: And, I mean, this is the closest we get to actually seeing a black hole in general, right? We're seeing this stuff. It's eating, getting sucked in. But in this case, all that dust and gas has stopped getting pulled in.

SHAPIRO: Do scientists know why? Like, what's actually happening?

BARBER: So not all black hole disks are created equal. Like, some feed black holes slowly, some faster. Some disks are thin. Some are fatter. And that's important, according to Yale astrophysicist Priyamvada Natarajan, who didn't work on this paper.

PRIYAMVADA NATARAJAN: So geometry is destiny, in many ways, for the gas that's falling into a black hole.

SCOTT: And that geometry she's talking about - or basically, you know, the shape of the disk - that determines how fast the material goes into the black hole. So the thicker the disk, the slower the dust and the gas fall in.

BARBER: And these thick disks can strengthen the magnetic fields present around black holes. That's what's happening here. Its disk is thick and now heavily magnetized. Now this magnetic pressure is strong enough to push against the black hole's gravitational pull and win.

NATARAJAN: It countervails the black hole's gravity. Nothing flows. The flow stops.

SCOTT: So basically, we have a massively constipated black hole.

SHAPIRO: On that image, Aaron, let's pivot to our third topic...

SCOTT: (Laughter).

SHAPIRO: ...Some good news about how farms can help tropical biodiversity. How does that work? Because often we hear about rainforests being chopped down to make way for farms, which is a bad thing for biodiversity.

SCOTT: Yeah. I mean, to be clear, Ari, of course, destroying tropical forests to create farmland does contribute a massive amount of carbon to the atmosphere, and it eliminates habitat for a lot of animals. But there is a bit of good news for some tropical birds, and they're kind of, I mean, the canary in the coal mine when it comes to biodiversity.

BARBER: Yeah. A new study out this week in the journal PNAS found that some birds that have been hurt by deforestation in Costa Rica, like the great green macaw - they've actually been increasing in numbers on what's known as diversified farms.

SHAPIRO: Like, farms that grow a lot of different crops - not just one.

SCOTT: Exactly, exactly. In the tropics, there are a lot of these smaller family farms, and they plant just this big mix of crops, all interspersed with patches of forests and native plants and shrubs. It's very different from the monocrop farmlands that we mostly see here in the U.S.

BARBER: And researchers at Stanford who have been tracking tropical birds in Costa Rica have found some of these diversified farms are actually great habitat for forest birds, which sort of goes against the conventional wisdom about farmland and wildlife.

SCOTT: Now, this increase in tropical birds that they're seeing on these diversified farms is not fully compensating for all the population losses that researchers are observing in the forests, but it is something. And, you know, the thought is that these diversified farms are providing a habitat that will act kind of as a bridge connecting shrinking forests that might otherwise end up fragmented, and that will help the birds hang on and some of them even thrive.

SHAPIRO: Does this offer any lessons for farms in the U.S.?

SCOTT: Yeah. I actually asked the lead author, Nicholas Hendershot, about that. And he said it's tricky to think about doing this in the U.S. just because of that large-scale agriculture that dominates here - you know, think your Midwestern cornfield. But Nicholas says we could think smaller, like people's gardens.

NICHOLAS HENDERSHOT: And just trying to make that as friendly for wildlife as possible - because I think what this work and other work shows is that wildlife are using everything, and they're not just in these protected forests.

SCOTT: And what's really cool about that is that there was also a study out last week in Scientific Reports that found, in Germany at least, there's a lot of potential for gardeners to play a role in conservation by planting threatened plants in their yards or even something like a balcony pot.

BARBER: So anyone with a little space to plant native species can provide habitat for things like threatened birds and pollinators.

SHAPIRO: That's Regina Barber and Aaron Scott of NPR's science podcast, Short Wave, where you can learn about new discoveries, everyday mysteries and the science behind the headlines. Regina, Aaron, thank you both.

BARBER: Thanks, Ari.

SCOTT: Thanks for having us.

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Aaron Scott
Aaron Scott (he/him) is co-host of NPR's daily science podcast, Short Wave. The show is a curiosity-fueled voyage through new discoveries, everyday mysteries and the personal stories behind the science.
Regina G. Barber
Regina G. Barber is Short Wave's Scientist in Residence. She contributes original reporting on STEM and guest hosts the show.