What Zombie Ants Are Teaching Us About Fungal Infections: Q & A with Entomologists David Hughes and Maridel Fredericksen

 

I can still remember that giddy feeling I had seven years ago, when I first read about the “zombie ant.” The story was gruesome and fascinating, and it was everywhere. Even friends and family who aren’t so interested in science knew the basics: in a tropical forest somewhere there’s a fungus that infects an ant and somehow takes control of the ant’s brain, forcing it to leave its colony, crawl up a big leaf, bite down and wait for the sweet relief of death. A grotesque stalk then sprouts from the poor creature’s head, from which fungal spores rain down to infect a new batch of ants.

A fungal fruiting body erupts through the head of a carpenter ant infected by a parasitic fungus in Thailand. Credit: David Hughes, Penn State University.

The problem is, it doesn’t happen quite like that. David Hughes Exit icon , the Penn State University entomologist who reported his extensive field observations of the fungus/ant interactions in BMC Ecology Exit icon, which caused much excitement back in 2011, has continued to study the fungus, Ophiocordyceps unliateralis, and its carpenter ant host, Camponotus leonardi.

In late 2017, Hughes and his colleagues published an article in PNAS Exit icon in which they used sophisticated microscopy and image-processing techniques to describe in great detail how the fungus invades various parts of the ant’s body including muscles in its legs and head.

Although Hughes’s earlier BMC Ecology paper showed fungus in the head of an ant, the new study reveals that the fungus never actually enters the brain.

To me, the new finding somehow made the fungus’ control over the ant even more baffling. What exactly was going on?

To find out, I spoke with Hughes and his graduate student Maridel Fredericksen.

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Cool Tools: Pushing the Limits of High-Resolution Microscopy

Cell biologists would love to shrink themselves down and actually see, touch and hear the inner workings of cells. Because that’s impossible, they have developed an ever-growing collection of microscopes to study cellular innards from the outside. Using these powerful tools, researchers can exhaustively inventory the molecular bits and pieces that make up cells, eavesdrop on cellular communication and spy on cells as they adapt to changing environments.

In recent years, scientists have developed new cellular imaging techniques that allow them to visualize samples in ways and at levels of detail never before possible. Many of these techniques build upon the power of electron microscopy (EM) to see ever smaller details.

Unlike traditional light microscopy, EM uses electrons, not light, to create an image. To do so, EM accelerates electrons in a vacuum, shoots them out of an electron gun and focuses them with doughnut-shaped magnets onto a sample. When electrons bombard the sample, some pass though without being absorbed while others are scattered. The transmitted electrons land on a detector and produce an image, just as light strikes a detector (or film) in a camera to create a photograph.

This image, showing a single protein molecule, is a montage. It was created to demonstrate how dramatically cryo-EM has improved in recent years. In the past, cryo-EM was only able to obtain a blobby approximation of a molecule’s shape, like that shown on the far left. Now, the technique yields exquisitely detailed images in which individual atoms are nearly visible (far right). Color is artificially applied. Credit: Veronica Falconieri, Subramaniam Lab, National Cancer Institute.

Transmission electron microscopes can magnify objects more than 10 million times, enabling scientists to see the outline and some details of cells, viruses and even some large molecules. A relatively new form of transmission electron microscopy called cryo-EM enables scientists to view specimens in their natural or near-natural state without the need for dyes or stains.

In cryo-EM—the prefix cry- means “cold” or “freezing”—scientists freeze a biological sample so rapidly that water molecules do not have time to form ice crystals, which could shove cellular materials out of their normal place. Cold samples are more stable and can be imaged many times over, allowing researchers to iteratively refine the image, remove artifacts and produce even sharper images than ever before. Continue reading

Cool Image: Adding Color to the Gray World of Electron Microscopy

Color electron micrograph of an endosome, a cell organelle. Credit: Ranjan Ramachandra, UCSD

As his Christmas gift to himself each year, the late biochemist Roger Tsien treated himself to two weeks of uninterrupted research in his lab. This image is a product of those annual sojourns. While it may look like a pine wreath dotted with crimson berries, it is in fact one of the world’s first color electron micrographs—and the method used to create it may dramatically advance cell imaging.

Electron microscopy (EM) is a time-honored technique for visualizing cell structures that uses beams of accelerated electrons to magnify objects up to 10 million times their actual size. Standard EM images are in grayscale and any color is added in with computer graphics programs after the image is made. With their new technique, Tsien, who received a Nobel Prize for his development of green fluorescent protein into a tool for visualizing details in living cells using light microscopes, and his colleagues have found a way to incorporate color labeling directly into EM. Continue reading