A living biosensor helps track bee health
A living biosensor helps track bee health

Scientists have created the first living biosensor to study the honey bee’s gut microbiome. Bacteria such as E. coli (E.coli), can be programmed to serve as biosensors for studying the mammalian gut microbiome. However, this has never been done for honey bees.

To truly understand the complex interplay of factors that dictate the role of microbiomes in the health of these endangered pollinators, the research team at the University of Lausanne in Switzerland needed to create a similar biosensor for their unique physiology.

Microbiomes are broad

The scope of the microbiome extends beyond simple digestion to behavior, development, and mental and physical health. In humans, researchers are still grappling with the complexity of the interactions that dictate how the hundreds of species of bacteria living in our guts affect our lives.

In bees, however, this complexity is reduced. “Honey bees are a very good model for studying the microbiota,” said Audam Chun, a postdoctoral researcher at the University of Lausanne in Switzerland. According to Chhun, a honey bee taken from anywhere in the world will have the same eight to ten types of bacteria in its gut.

Honey bees are also easy to work with in the laboratory, and because they are social insects, their behavior reveals connections along the gut-brain axis. But like all gut research, peering inside is no easy task.

Living biosensors

Advances in synthetic biology, which includes our ability to manipulate and add genes into different organisms, first led to the ingenious idea of ​​using gut bacteria as living sensors to read the molecules and state of the gut.

These bacteria are engineered to produce proteins that act as simple chains. Generally, these chains contain a sensor protein that binds the target of interest and another signaling protein that researchers can then visualize in the lab. These biosensors are harmless and allow researchers to track molecules present in the gut.

Currently, biosensors are made with E. coli because it naturally colonizes the gut of mammals and many genetic engineering techniques have already been developed for this species. Unfortunately, E. coli does not live in the gut of the honey bee, so designing a biosensor for this species required Chhun and his colleagues to start from scratch.

The first step was to identify which bee gut bacteria were most amenable to genetic engineering. Initial experiments revealed Snodgrassella alvi (S.alvi) as the best candidate. The synthetic biology techniques used to add genes to bacteria then had to be adapted and optimized S. alvi.

One common technique for adding genes to bacteria is via a plasmid. In bacteria, DNA exists in circular units called plasmids. Researchers insert new plasmids into a bacterium that contains the new genes, or chain of genes, they want the bacteria to express.

For testing whether a S. alvi biosensor can work and survive in honeybees, Chhun inserted a plasmid containing a simple genetic circuit that detects a sugar derivative called isopropylthio-β-galactoside (IPTG) and that produces a green fluorescent protein in response. Chhun chose IPTG as a target because they could add different concentrations of it to the honey bee’s food and measure how much, if any, fluorescent protein was produced.

But there was one problem: getting the bees to escape the lab.

Bee massages

To see the changes in fluorescence produced by the sensors, researchers working with mammals simply collect stool samples. With bees, however, this is not so simple due to the insects’ impressive hygiene.

As Chun explained, bees always leave the hive to defecate. “So when we keep them in the lab in cages, for them it’s the hive,” Chun said, “and because they don’t go outside, they don’t defecate, they just keep it inside.”

Faced with a lab full of constipated bees, Chun and his colleagues turned to a low-tech solution: massage. “If you just massage them, then they will defecate,” he said.

To massage them without being stung, they used the insect’s inability to withstand low temperatures. “If you put them on ice, they fall asleep,” Chun said, “then we just massage the abdomen and make them poop into a tube.”

Fluorescent bee droppings

The massaging worked and there was a noticeable change in stool fluorescence corresponding to an increasing concentration of IPTG in the honey bee’s diet.

It’s an exciting proof of concept, but according to Chhun, some tweaking is still needed. “One of the things we could improve is that this biosensor system is permeable,” he said, meaning that even in the absence of IPTG, there was always some fluorescence. “If we want to study other molecules, especially perhaps a low concentration of a molecule, we need to set up the system so that the basal level of expression is very, very low,” he said.

Once this first step is achieved, the team now works on the design S. alvi sensors that detect other molecules of interest to microbiome researchers. Ultimately, he aspires to design sensors with memory as well. “There are a lot of molecules in the gut that are transient,” Chun said, “and we want our sensor to be able to tell us, well, that was five days ago, but five days ago there was this molecule.”

With such a tool, microbiome researchers can begin to track how the microbiome communicates with the host and influences health. Biosensors can also serve as monitors for the health and conservation of honey bees, although the ethical discussions about introducing engineered bacteria to wild bees are far from resolved.

Reference: Audam Chhun, et al. Engineered bacterial symbiont enables non-invasive biosensing of the honey bee gutPLOS Biology (2024), DOI: 10.1371/journal.pbio.3002523

Main image credit: Aduam Chhun, et al.

By admin

Leave a Reply

Your email address will not be published. Required fields are marked *