See the First 3D Images of Bacteria's 'Biological Wheels'

Believe it or not, humans didn't invent the wheel. Long before we showed up, some of nature's tiniest organisms had already evolved wheel-like nanostructures to propel themselves through liquid media. Now, scientists have found a way to image bacteria's naturally occurring, biological wheels for the first time, New Scientist reports.

Most bacteria maneuver themselves around using tiny protein motors that power a spinning flagellum tail, which is no more than tens of nanometers wide. While scientists know that different motor structures produce different levels of mobility in bacteria, they haven't been able to study the details of these mechanisms—until now. According to the study recently published in the journal PNAS [PDF], researchers at Imperial College London used an electron microscope to capture the first-ever 3D renderings of these structures, which you can see below.

By freezing the bacteria through a process called electron cryo-tomography, they were able to image the motors from multiple angles. They looked at a handful of various bacteria samples—including Campylobacter and Salmonella—to see how their wheels differed. Flagella generate their torque from wheel-like structures around the motor called stators. Different bacteria have different amounts of stators, which in turn come in different shapes, sizes, and strength levels. Campylobacter, which has nearly double the stators of Salmonella, has enough propulsion power to penetrate your stomach lining.

The high-resolution images could be used by nanoroboticists to develop better motors in the future, or they could find a way to incorporate the biological wheels into their robots to avoid building them from scratch. Better understanding the mechanisms behind the structures could also help us to target harmful bacteria more efficiently. You can read the full report in PNAS.

Vibrio motor // Imperial College London

Salmonella motor // Imperial College London

Campylobacter motor // Imperial College London

[h/t New Scientist]

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How Does Catnip Work?
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If you have a cat, you probably keep a supply of catnip at home. Many cats are irresistibly drawn to the herb, and respond excitedly to its scent, rubbing against it, rolling around on the floor, and otherwise going nuts. There are few things that can get felines quite as riled up as a whiff of catnip—not even the most delicious treats. But why does catnip, as opposed to any other plant, have such a profound effect on our feline friends?

Catnip, or Nepeta cataria, is a member of the mint family. It contains a compound called nepetalactone, which is what causes the characteristic catnip reaction. Contrary to what you might expect, the reaction isn’t pheromone related—even though pheromones are the smelly chemicals we usually associate with a change in behavior. While pheromones bind to a set of specialized receptors in what’s known as a vomeronasal organ, located in the roof of a cat's mouth (which is why they sometimes open their mouths to detect pheromones), nepetalactone binds to olfactory receptors at the olfactory epithelium, or the tissue that lines the mucus membranes inside a cat’s nose and is linked to smell.

Scientists know the basics of the chemical structure of nepetalactone, but how it causes excitement in cats is less clear. “We don’t know the full mechanisms of how the binding of these compounds to the receptors in the nose ultimately changes their behavior,” as Bruce Kornreich, associate director of the Cornell Feline Health Center, tells Mental Floss. Sadly, sticking a bunch of cats in an MRI machine with catnip and analyzing their brain activity isn’t really feasible, either from a practical or a financial standpoint, so it’s hard to determine which parts of a cat’s brain are reacting to the chemical as they frolic and play.

Though it may look like they’re getting high, catnip doesn’t appear to be harmful or addictive to cats. The euphoric period only lasts for a short time before cats become temporarily immune to its charms, meaning that it’s hard for them to overdo it.

“Cats do seem to limit themselves," Michael Topper, president of the American Veterinary Medical Association, tells Mental Floss. "Their stimulation lasts for about 10 minutes, then it sort of goes away.” While you may not want to turn your house into a greenhouse for catnip and let your feline friend run loose, it’s a useful way to keep indoor cats—whose environment isn’t always the most thrilling—stimulated and happy. (If you need proof of just how much cats love this herb, we suggest checking out Cats on Catnip, a new book of photography from professional cat photographer Andrew Martilla featuring dozens of images of cats playing around with catnip.)

That said, not all cats respond to catnip. According to Topper, an estimated 70 percent of cats react to catnip, and it appears to have a genetic basis. Topper compares it to the genetic variation that causes some individuals to smell asparagus pee while others don’t. Even if a cat will eventually love the smell of catnip, it doesn’t come out of the womb yearning for a sniff. Young kittens don’t show any behavioral response to it, and may not develop one until several months after birth [PDF].

But some researchers contend that more cats may respond to catnip than we actually realize. In one 2017 study, a group of researchers in Mexico examined how cats might subtly respond to catnip in ways that aren’t always as obvious as rolling around on the floor with their tongue hanging out. It found that 80 percent of cats responded to catnip in a passive way, showing decreased motor activity and sitting in the “sphinx” position, an indicator of a relaxed state.

There are also other plants that have similar effects on cats, some of which may appeal to a wider variety of felines than regular old catnip. In a 2017 study in the journal BMC Veterinary Research, researchers tested feline responses to not just catnip, but several other plants containing compounds similar in structure to nepetalactone, like valerian root, Tatarian honeysuckle, and silver vine. They found that 94 percent of cats responded to at least one of the plants, if not more than one. The majority of the cats that didn’t respond to catnip itself did respond to silver vine, suggesting that plant might be a potential alternative for cats that seem immune to catnip’s charms.

Despite the name, domestic cats aren’t the only species that love catnip. Many other feline species enjoy it, too, including lions and jaguars, though tigers are largely indifferent to it. The scent of the plant also attracts butterflies. (However, no matter what you’ve heard, humans can’t get high off it. When made into a tea, though, it reportedly has mild sedative effects.)

The reason Nepeta cataria releases nepetalactone doesn’t necessarily have to do with giving your cat a buzz. The fact that it gives cats that little charge of euphoria may be purely coincidental. The chemical is an insect repellant that the plant emits as a defense mechanism against pests like aphids. According to the American Chemical Society, nepetalactone attracts wasps and other insect predators that eat aphids, calling in protective reinforcements when the plant is in aphid-related distress. That it brings all the cats to the yard is just a side effect.

Because of this, catnip may have even more uses in the future beyond sending cats into a delighted frenzy. Rutgers University has spent more than a decade breeding a more potent version of catnip, called CR9, which produces more nepetalactone. It’s not just a matter of selling better cat toys; since catnip releases the compound to ward off insects, it’s also a great mosquito repellant, one that scientists hope can one day be adapted for human use. In that case, you might be as excited about catnip as your cat is.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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A Baby's Cries Might Hint at What the Child Will Sound Like as an Adult
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Babies may be incapable of talking, but at just a few months old, they've already developed many of the characteristics that will one day make their speaking voice distinct. That's the takeaway from a new study, reported by The New York Times, in which a team of bioacoustic researchers found that you can tell what infants will sound like at age 5 by analyzing their cries.

For their study, published in the journal Biology Letters [PDF], the researchers recorded the voices of 15 French children 4 to 5 years old. They then compared the clips to the children's "mild discomfort cries" recorded when they were 2 to 5 months old. The results showed that a baby's voice can be used to predict 41 percent of the variances they will have in their vocal pitch at age 5.

Other studies have suggested that what our voices sound like when we're young is a strong indicator of what they will sound like later on—even after puberty changes our vocal cords. A boy's voice pitch at age 7 can predict up to 64 percent of the distinguishing features his voice will have as an adult.

The study authors write that many of these variances may develop before childhood, and potentially in utero: "These observations suggest that inter-individual differences in [voice pitch] arise early in life and are largely unaffected by puberty, and raise the possibility that [pitch] may even be determined before birth."

The most important markers that determine pitch are the length, size, and tension of our vocal folds. But those aren't the only determinants: Environmental factors like smoking, pollution, and climate can affect how our voices sound as well, though these changes are usually temporary.

[h/t The New York Times]

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