November 19, 2013

Bacteria in the Gut May Affect Health

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Despite the many efforts we make to eat healthy and obtain all recommended nutrients, new research suggests that we are not the only ones in charge of our health. Prof. Angela Douglas, entomology and molecular biology and genetics, thinks there may be microorganisms in animals’ digestive tracts that can influence nutrient acquisition and allocation.

In order to investigate this theory, Douglas’ research team studied the effects of microbiota, or readily culturable bacteria, on the digestive systems of Drosophila, commonly known as fruit flies.

A technological breakthrough in genome sequencing techniques allowed Douglas’ team to move from studying one-microbial interactions to more complex interactions. This new technique made it possible to identify and count the microorganisms in the digestive tract and determine their capabilities.

“If you want to study how microorganisms interact with a host, you have to, in a sense, tear the association apart,” Douglas said. “ You have to get the isolated microorganisms and germ-free animal and put them back together again.”

To obtain germ-free animals, Douglas’ team put each drosophila egg into household bleach which dissolved away the eggshell, leaving an intact embryo.

The embryo then was transferred into a container of sterile food, so that the flies would continue to be raised in a germ-free environment. These germ-free flies were then compared to flies raised in a natural environment, whose guts contained microbiota.

Douglas found a dramatic difference between the animals exposed to bacteria and the germ-free animals. Although the animals weighed the same amount, the germ-free animals were fat. They contained a higher lipid content and had higher levels of circulating glucose. Douglas said she was surprised to find that the higher lipid content was not a result of increased eating; instead, it was instead due to hypophagia, or reduced feeding, in the germ-free flies.

“It was quite clear that the microbiota were influencing how nutrient allocation decisions were made,” Douglas said.

According to Douglas, although the exact mechanism by which microorganisms and their host animals interact is unknown, it was evident that the microbiota were modulating signaling networks in nutrient allocations in the flies’ bodies.

Nevertheless, Douglas said that these results were not the same for all of the flies that were researched. Providing different lines of flies with bacteria had a different effect depending on the genotype of each organism.

“I think this is telling us very clearly that microorganisms are interacting with the genetic makeup of these flies,” Douglas said. “You can’t predict the phenotype of the animal on the basis of its genotype alone. It’s [phenotype] is also influenced by its interactions with the microorganisms and other environmental factors.”

At the moment, Douglas is investigating which genes are important. Despite humans’ higher body temperature and anoxic, or low-oxygen, digestive system, the simple system in Drosophila can serve as a model to study interactions and to understand how the presence of microorganisms can influence human health, according to Douglas.

According to Douglas, there is a lot of interest regarding how microorganisms in humans’ digestive tracts influence health and propensity for obesity. She said that other studies have indicated that people of different body mass indices can have different compositions of microbiota inside their digestive systems. Douglas is starting to conclude from her data that resident microbiota interact to shape how fat or lean humans are.

“If our data on these fruit flies are relevant to humans, it may be that a therapeutic combination of a particular bacteria may help many people become leaner, but actually may have the reverse effect on people of certain genetic makeups. We need to be careful in the therapeutic use of these microbial concoctions,” Douglas said.