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2-25-20

Engineered bacteria protect honey bee health

• Bacteria naturally found in honey bees were engineered to help bees fight infections that that have been destroying colonies.
• More studies are needed before the engineered bacteria could be tested in beehives in the wild.

Honey bees are vital to agriculture around the world. About a third of crops, and most flowering plants, require pollinators such as bees to reproduce. Recently, several threats to honey bee health have increased the incidence of colony collapse, where most bees in a hive suddenly disappear.

One major threat is from a type of parasitic mite called Varroa destructor. These mites live on bees and puncture their bodies to feed on fat cells. The parasites alone can harm or kill bees. But when the mites feed, they can also pass a deadly virus called deformed wing virus (DWV) to the bees.

Together, these two pathogens are thought to be major contributors to colony collapse. Hives can be treated with pesticides to kill mites and protect bees, but mites quickly develop resistance to such chemicals. The pesticides can also contaminate honey.

As an alternate strategy, researchers have tried introducing double-stranded RNA (dsRNA) into bee colonies. This type of RNA is produced by viruses, including DWV. When insect immune systems encounter dsRNA, they respond by attacking similar RNA sequences. This immune reaction could potentially kill viruses throughout a bee's body.

Past attempts to use this strategy, however, have proven expensive and short-lived. New research from a team led by doctoral candidate Sean Leonard and Drs. Jeffrey Barrick and Nancy Moran from the University of Texas explored a way to improve the use of dsRNA to protect bees from their pathogens.

The researchers engineered a type of bacterium found in the normal bee microbiome to produce dsRNA matching that of either DWV or Varroa mites. After re-introducing the bacteria to small groups of bees, the team tested whether the bees were better able to survive infection from the pathogens. The work was funded in part by NIH's National Institute of General Medical Sciences (NIGMS). Results were published on Jan. 31 in Science.

The researchers successfully reintroduced the engineered bacteria to bees through their food and showed that the dsRNA produced in the gut spread to other parts of the bees' bodies. They also showed that it could provoke an immune response in the bees.

The team next tested bacteria carrying dsRNA targeting different parts of the DWV genome. Exposure to bacteria with one of these dsRNAs substantially improved the bees' survival when they were later injected with DWV virus.

In another set of experiments, the team engineered the bacteria to produce dsRNA from the Varroa mite genome and reintroduced the bacteria to bees. When Varroa mites fed on the bees, they took the dsRNA from the bacteria into their own bodies. This dsRNA then triggered the mites' immune system to attack their own cells. Mites that fed on bees carrying the engineered bacteria died more quickly than mites that fed on bees without the protective bug.

"This is the first time anyone has improved the health of bees by genetically engineering their microbiome," Leonard says.

More research is needed before the bacteria could be introduced to hives in the wild, including testing how the engineered bacteria might spread and whether the engineered genes could pass to other types of bacteria.

-by Sharon Reynolds

For further information on this and other health topics, visit the web site of the National Institute of Health at www.nih.gov.