Genetic diversity key to honeybee health

LINDELL BEACH, B.C. — A new study has discovered that greater genetic diversity in worker bees leads to colonies with fewer pathogens and a greater number of helpful bacteria to ward off disease.

The study documented the communities of active bacteria harboured by honeybee colonies. It also identified four important microbes in honeybees previously associated with fermentation with humans and other animals.

The research was recently published online in PloS ONE.

“There’s a huge diversity of organisms out there,” said Irene L.G. Newton, assistant professor with Indiana University’s biology department.

“We keep finding more and more diverse microbes. We extracted segments of their genome from bee guts and from the food products they make. We were able to use the sequence information to try to determine what these organisms were. This is equivalent to a little tag, or bar code if you will.”

The four organisms highlighted in the research paper were chosen because of their contribution to food processing or fermentation habitats.”

Two of the microbes that were dominant in the study were Succinivibrio, associated with cattle rumens, and Oenococcus, associated with wine fermentation.

Newton said the research suggests honeybees may take advantage of these beneficial symbiotic bacteria to convert indigestible material into nutritious food and enhance protection from pathogens.

The other two important microbes are Paralactobacillus (food fermentation) and Bifidobacterium (yogurt). There was 40 percent greater activity of these two probiotics in bee colonies that were genetically diverse compared to those that were genetically uniform.

“Vegetarian organisms need a diverse diet in order to get their full set of aminoacids (and other nutrients),” said Newton.

“In order to accomplish this, bees harvest a diverse array of different pollen types and nectar types. They inoculate the pollen they collect with their own microbes and then they let it sit in the honeycomb in the hive for days before they actually consume it.

“There is a process that has to go on for this pollen and the nutrients in the pollen to be accessible to them. We postulated that this is something being done by the microbes (they use) for inoculating. It’s like the bees are running their own little fermentation (process) to get the nutrients they need. That’s the functional aspect of their community.”

The researchers sampled and classified more than 70,500 genetic sequences for bacterial genera from 10 genetically uniform colonies and 12 genetically diverse colonies by analyzing a specific molecule found in RNA. It is one of the three major macromolecules, along with DNA and proteins, that are essential for all life forms.

The RNA study was a first for examining honeybees and their symbiotic microbes. It is the single largest analysis of newly identified active microbes to be identified in honeybees.

They were also able to show that those microbes were more diverse in genetically diverse colonies (1,105 unique bacterial species) compared to genetically uniform colonies (781 species).

According to the researchers’ report, not all nutrients in pollen are easily available because each grain has a cell wall that is hard to break down. Remains of only partially digested pollen grains can be found in the gut of worker bees.

In addition, no single pollen source will provide all the bees’ nutrients, which is why they must collect a mix of pollen types.

The bees pack the pollens they collect into the honeycomb, add glandular secretions and seal it with honey.

After several weeks, it matures into bee bread, which “has a higher vitamin content, lower amounts of complex polysaccharides, a shift in amino acid profile, and lower pH.”

It is possible, but not yet definitively identified, that the microflora in the stored pollen is actively involved in the metabolic change.

“Our primary goal of the study was to look at their genetic diversity in the hive and how that contributes to their health,” said Newton.

“We don’t know how this different community is generated. So what we determined was that the bacteria associated with genetically diverse colonies are more healthful, have fewer pathogens, a greater number of probiotic species and they’re more diverse. There are a greater number of different organisms in diverse colonies than there are in the genetically uniform colonies. What is the mechanism, what is the emergent properties of these colonies that create the different microbiota?”

They hope experiments planned this summer will provide answers.

Newton said genetically uniform colonies had a higher activity of potential plant and animal pathogens in their digestive tract than workers from genetically diverse colonies by as much as 127 percent.

Wellesley College assistant professor Heather Mattila has been investigating the benefits of genetic diversity in honeybees for years and was thrilled to have Newton’s microbial expertise incorporated into the project.

“This is an exciting result because it gives us insight into how individual bees and their symbionts can en-hance the overall health of a colony when it is genetically diverse,” she said.

Genetic diversity is created in a colony when a queen mates with many male bees, an act known to improve colony health and productivity and may prove critical in fending off colony collapse disorder (CCD).

The U.S. Department of Agriculture says CCD has taken 34 percent of the U.S. honeybee population every year since 2007, while the annual rate of loss in Canada has been reported to be approximately 36 percent.

“We don’t know what’s causing colony collapse disorder, but colonies that succumb to it suffer from a broad range of problems,” said Newton.

“What we observed in our work was that there was less likelihood of potentially pathogenic bacteria showing up in genetically diverse honeybee colonies compared to genetically uniform colonies.”

Exactly how this works is still a mystery. A honeybee colony is a eusocial superorganism where all the worker bees work for the common good of the hive.

Newton said there is a single reproductive member, the queen bee, which mates with a large number of males. The offspring are diverse because they come from many different fathers.

Mattila wrote in the report that this extreme polyandry by queens is a highly derived trait and found universally in the honeybee genus Apis.

“Honeybees benefit from the high level of within-colony genetic div-ersity that extreme piolyandry generates through an increased ability to mitigate symptoms of pathogen and parasite infections and higher levels of colony stability and productivity.”

Newton said that not only would there be an entirely different kind of immune response that could fight off different kinds of pathogens, but a different kind of microbiome would also emerge in a genetically diverse colony.

She said there’s been a trend in western agriculture to reduce diversity in genetic stock and increase monoculture.

“People have noted for a very long time that this ultimately reduces fitness in the organism, especially with regards to syndromes of infection,” she said.

“So it would not be surprising if it turns out that genetic diversity was a major correlate in preventing CCD. That said, we do not yet know if it is directly involved, but we suspect if you have a healthier hive and you know what makes a healthier honeybee, then you might be able to defend the honeybee against these kinds of syndromes.”

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