Do not eat the forbidden pink berries (because they consist of bacteria)

This cluster of pink beauty might remind you of a sea of ​​cherry blossoms, or a juicy raspberry compote waiting to ooze over your pancakes. Well, we’re afraid you might want to put these beautiful images aside right away. What you’re looking at here are bacteria, and while these structures may be called “pink berries,” we can assure you they don’t make for a tasty snack.

But while they certainly belong on the list of scientific oddities you shouldn’t eat, pink berries are still a fascinating microbial phenomenon.

Bacteria often discover that there is strength in numbers. Some of the most troublesome bacterial infections in humans are caused by biofilms, layers of microbes covered in a sugary coating that can colonize wounds or wrap around medical devices such as catheters. Because they are clustered together in this way, it is difficult for antibiotics to gain a foothold.

Pink berries are a very specific type of bacterial aggregate that only forms under certain conditions. They are most commonly found coating the surface of submerged sediment in salt marshes, giving the pools a pinkish hue.

At low tide, pink berries are visible in a pool at Great Sippewissett Marsh, Woods Hole, Massachusetts.

Pink berries in a pool at Great Sippewissett Marsh, Woods Hole, Massachusetts.

Image credit: Lizzy Wilbanks

Under the microscope you can see how the individual cells have clustered together to form a berry shape, held together by a shiny transparent polymer coating. The characteristic pink color comes from a species called Thiohalocapsa PSB1, which makes up the largest part of the cluster. This species can generate its own food using sulfur and light. Genetically similar individuals cuddle with symbiotic species that work together to create zones free of oxygen – which is toxic to the bacteria – and their combined weight ensures that the berries nestle well into their environment.

pink currant on a black background

This berry has a diameter of approximately 3 millimeters.

Image credit: Scott Chimileski

But there is a downside to all this closeness. As humanity recently discovered with COVID-19, it’s best to keep your distance from others when a virus strikes — but if you’re a bacteria in a pinkberry, that’s not really an option.

“It’s the perfect cocktail to let an epidemic sweep through and wipe out everything,” said Lizzy Wilbanks, a microbiologist who has been interested in pink berries since she first encountered them in high school, in a statement.

Wilbanks and colleagues recently conducted a study to learn how Thiohalocapsa sidesteps these issues when faced with a viral threat.

The bacteria use a nifty genetic trick called diversity-generating retroelements (DGRs). Parts of the DNA are transcribed into RNA and then back into DNA, a process that tends to introduce errors. These sequences are then inserted into a target gene, adding a lot of new genetic variation at specific locations in the bacterial genome. Similar systems exist in other organisms, but scientists have not yet fully understood how they work.

The new study revealed that many of the objectives of DGRs in Thiohalocapsa are components similar to those found in the immune systems of more complex organisms, including humans. Examination of hundreds of pink berries revealed that variation in these genes changed depending on the environment, which could reflect differences in the viruses present in different pools in a salt marsh.

More work needs to be done to fully unravel how Thiohalocapsa may manipulate its genome to evade pathogens, but the possibilities for this research extend beyond microbiology and even have implications for our understanding of human evolution.

“It tells us about the challenges we faced when we were little balls of cells,” says Wilbanks. “When you’re forming multicellular structures, you have to develop some fancy immune defense mechanisms to stay alive.”

Now that we have all this to offer to the scientific community, we think we can forgive the pinkberries for catfishing us.

The research has been published in PNAS.

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