Friday, April 09, 2010

gut bacteria are what we eat

The Scientist | Japanese people regularly consume sushi wrapped in seaweed, which carries with it marine bacteria that produce porphyranases. "It was directly obvious for us that this was horizontal gene transfer from the ocean to the Japanese gut," Hehemann said. "As far as I know, there has not before been an example of horizontal gene transfer between different ecosystems."

In a commentary accompanying the study, Sonnenburg compared the gene transfer event to giving human gut bacteria a "new set of utensils" -- likely providing them the ability to digest specific foods prevalent in different regional diets. "I think there's a good bet that you'll see diet match microbiota functionality over and over and over again," he said. "That's exactly what we see in this study."

But the food purification and sterilization techniques commonly used throughout the industrialized world might affect the environmental tuning of the human gut biome function suggested by the study, Sonnenburg added. Removing many harmful bacteria from foods has dramatically reduced food-borne diseases in recent decades, he said, "but I think there's a likely cost -- the loss of microbes that are not harmful." Such microbes may transfer seemingly beneficial genes to the gut biome, increasing its ability to adapt to changes in diet, as well as fine-tune the immune system, such that "if you begin to eradicate microbes with which we have coevolved, that has the potential [to disrupt] homeostasis," Sonnenburg said.

"It shows how we rely on biodiversity that is surrounding us," Hehemann agreed. "Maybe that's the natural way -- that there is a frequent update of our gut microbiome [through] gene transfer to increase gene diversity. Obviously when we eat these highly processed foods, that's not going to happen."

How exactly this gene transfer helps the host, however, is still unclear, said Hehemann, who is currently looking into the benefits porphyranase genes provide gut bacteria in his new lab at the University of Victoria in British Columbia, Canada. It's possible that when the bacteria break down marine algae polysaccharides, it benefits the host through the production of short chain fatty acids, the end product of bacterial metabolism, which can be taken up by the host in the form of calories, Sonnenburg said. "Those are calories that, in the absence of this capability, go totally unrealized."