Mice interacting

About receptors that recognize germ waste; muons that can make out mini-tsunamis; and plants can up their photosynthetic game

A Truly Curious correspondent

Byproducts of germs in the blood can affect processes in the body, such as immunity, metabolism, and brain function.

These byproducts are detected by special proteins studded on cells, called pattern recognition receptors (PRRs), that signal the presence of viruses, bacteria, or fungi.

Some bacterial products influence brain activity, and the PRRs are associated with brain disorders. It is not clear whether brain neurons directly sense bacterial components, or if bacteria influence how body processes work by first influencing brain neurons.

A mouse brain
A mouse brain. NIH / Public Domain

One such receptor, Nod2, helps the immune system recognize the presence of bacteria from lingering fragments of their cell walls (called muropeptides). Now, Nod2 in mice has been shown to play a role in various metabolic and nerve-related problems. The team of Ilana Gabanyi and others from the Institut Pasteur, along with others, found that Nod2 operates throughout the brain in the mice studied, including in the hypothalamus.

The hypothalamus is what acts as a bridge between our nervous and hormonal systems, playing an important role in temperature regulation, hunger, thirst, attachment and more.

Nod2ing off

If the gene for Nod2 was knocked out, mice – particularly older female mice – exhibited altered temperature regulation and feeding behavior, suggesting that Nod2 in the brain was sensing the presence of bacteria. In addition, they saw that muropeptides could reach the brain and regulate neurons once there.

Their work suggests that the brain can sense changes in gut bacteria and that information could become the basis for future therapies

Click here for the original paper (Paywalled, though the first author or other corresponding authors could perhaps provide the complete pdf)

The muon detector in the Tokyo Bay road tunnel
The muon detector in the Tokyo Bay road tunnel. Pic courtesy Tanaka et al., Scientific Reports / CC BY 4.0

Muon detectors on an underwater road find mini-tsunamis

Muons which are about 200 times the mass of their close relatives, the electrons that whiz around in atoms, are produced when cosmic rays slam into the atoms in the atmosphere. Researchers at the University of Tokyo have used them at the bottom of the sea to measure the volume of water above. The method is similar to x-ray imagery, but muons have far more energy and stronger penetration than x-rays do. Though most muons go right through everything, including us, water does scatter some muons – and the more the water, the more the scattering. The change seen gives scientists a measure of rises and drops in water levels – as seen in tides, sea levels and other changes.

A storm in a detector

In September 2021, a detector in an underwater highway in Japan – the Tokyo-Bay Seafloor Hyper-Kilometric Submarine Deep Detector – noted a variation in the usual changes seen in the water above: a small tsunami raised by a typhoon 400 km (250 miles) away. Such meteotsunamis result in water oscillations similar in some ways to those caused by earthquakes.

This is the first time that a muon detector, perhaps the only one in a public road tunnel, has detected tsunamis caused by weather.

In a press release, Hiroyuki Tanaka a professor at the University of Tokyo, said, “Similar systems are already being trialed in the U.K. and Finland. Obviously, an undertaking like this comes with challenges and installing delicate instruments in a busy tunnel could be difficult.”

Click here for the original paper

A comparison between C3 and C4 plants
A comparison between C3 and C4 plants. Pic courtesy socratic.org / CC BY-NC-SA 4.0

Ancient enzyme may decide the future of some plants

In modern times, we need plants that are better at sucking up carbon dioxide.

Mind you, these plants, and other living things that use photosynthesis, do a heroic job of soaking up the gas and replenishing the planet’s oxygen. But they work their magic using what researchers recently – and charitably – described as “a remarkably inefficient enzyme named Rubisco that fixes atmospheric CO2 into organic compounds.

Researchers want to make Rubisco (its more formal name being ribulose-1,5-bisphosphate carboxylase oxygenase) more efficient in processing carbon dioxide as its level rises since it mediates the first stage of carbon fixation in plants, algae and cyanobacteria, among others.

The history of an enzyme

Rubisco showed up in organisms more than 2.5 billion years ago, even before oxygen levels rose sharply on Earth, but thereafter, it specifically targeted carbon dioxide, though it continued to confuse it with oxygen. Plants relying on this earlier form of photosynthesis are called C3, because the first carbon compound produced had three carbon atoms. Because of their problem in differentiating oxygen from carbon dioxide, they also created a toxic two-carbon compound using oxygen. But it worked, didn’t it?

Around 30 million years ago, around the carbon dioxide levels began dropping from very high levels earlier, about 3% of plant species (though that makes up the vast majority of the grasslands), upped their game, and became better at targeting carbon dioxide. These plants, called C4, because, well, the first compound produced had four carbon compounds, sequestered more carbon. C4 plants rely on another enzyme – phosphoenolpyruvate carboxylase – that is better at targeting carbon dioxide. They can handle higher temperatures, and need less water and oxygen. But most C3 plants cannot.

Researchers Myat Lin and others at Cornell decided to find out what the ancestral Rubisco might have looked like. By comparing versions of the enzyme in the Solanaceae family – consisting of C3 plants as diverse as potato, eggplant, tomato and tobacco – the team developed a computational composite sketch of what the ancestral Rubisco may have looked like 20 to 30 million years ago.

As the researchers described it in their paper, “We found several enzymes with higher … efficiency in each of the four ancestral groups, indicating that all these enzymes probably evolved at higher CO2 levels.

So they have a good model and having “resurrected” ancient Rubiscos using a bacteria called Escherichia coli (yup, the same thing you find in your gut). Now, they plan to insert it into tobacco and see if it chugs in carbon dioxide more efficiently.

Click here for the original article

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