Gut Microbiome

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Gut Microbiome

The Scientist: _Gut bacteria are what we eat - The Scientist - Magazine of

the Life Sciences_

(http://www.the-scientist.com/blog/display/57272/#ixzz0kbntjTB2)

_http://www.the-scientist.com/blog/display/57272/#ixzz0kbntjTB2_

(http://www.the-scientist.com/blog/display/57272/#ixzz0kbntjTB2) Page 1 of

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Gut microbes, which help humans degrade otherwise indigestible plant

material, acquire some crucial digestive enzyme genes from the bacteria in the

food we eat, according to a study published this week in Nature. This new

finding provides an example of horizontal gene transfer by which diet can

influence the genetic diversity and functionality of the human gut microbiome.

 

" It's a fascinating story, " said microbiologist _Jeffrey Gordon_

(http://gordonlab.wustl.edu/) of Washington University School of Medicine in

St.

Louis, who did not participate in the study. " It shows that there's a

dimension to human evolution that's occurring at the level of our gut

microbiome. "

 

" This is an exciting development, " agreed microbiologist _Justin

Sonnenburg_

(http://med.stanford.edu/profiles/microimmuno/researcher/Justin_Sonnenburg/) of

Stanford University School of Medicine, who also was not involved

in the research. " I think we're at the tip of the iceberg here. Human diet

is so diverse, I think that we're just getting an initial glimpse of what's

likely to be really huge area of variation that differentiates populations

of humans. "

 

The human digestive tract harbors trillions of bacteria, many of which

establish lifetime, symbiotic relationships with their hosts. The food we eat

nourishes our gut flora, and those bacteria feed us with the products and

byproducts of their own digestive activities. Consequently, the gut

microbiome has evolved to encode a variety of digestive enzymes, for example,

those

that break down hard-to-digest polysaccharides in food plants, such as

celery, broccoli, and other vegetables.

 

As a PhD student at the _Station Biologique de Roscoff_

(http://www.sb-roscoff.fr/) in France, biochemist and co-author on the Nature

paper

Jan-Hendrik Hehemann was interested in a different type of enzymes -- bacterial

catalysts that break down polysaccharides in marine algae, which contain

sulfates not found in typical food plants. Hehemann and his colleagues

identified several genes that they suspected to code for those specialized

enzymes

in a recently sequenced marine bacteria genome and tested their activity on

red algae extracts. Their results revealed that the enzymes encoded by two

of the genes represent a whole new class of carbohydrate-digesting proteins,

capable of degrading porphyrans -- a unique component of marine plant

polysaccharides.

 

Mining the databases for other marine bacteria that might also contain

these so-called porphyranases, Hehemann instead stumbled upon a gut bacterium

found in human populations inhabiting Japan (but not North America). The

similarities between the genomes of the two bacteria suggested that gut

microbe had somehow obtained those genes directly from the marine species. " I

was really blown away by this result, " he recalled.

 

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. "