{"id":519684,"date":"2010-04-07T13:00:42","date_gmt":"2010-04-07T17:00:42","guid":{"rendered":"http:\/\/blogs.discovermagazine.com\/notrocketscience\/?p=1283"},"modified":"2010-04-07T13:00:42","modified_gmt":"2010-04-07T17:00:42","slug":"gut-bacteria-in-japanese-people-borrowed-sushi-digesting-genes-from-ocean-bacteria-not-exactly-rocket-science","status":"publish","type":"post","link":"https:\/\/mereja.media\/index\/519684","title":{"rendered":"Gut bacteria in Japanese people borrowed sushi-digesting genes from ocean bacteria | Not Exactly Rocket Science"},"content":{"rendered":"

\"Sushi\"Japanese people have special tools that let them get more out of eating sushi than Americans can. They are probably raised with these utensils from an early age and each person wields millions of them. By now, you\u2019ve probably worked out that I\u2019m not talking about chopsticks.<\/p>\n

The tools in question are genes that can break down some of the complex carbohydrate molecules in seaweed, one of the main ingredients in sushi. They are wielded by the hordes of bacteria lurking in the guts of every Japanese person, but not by those in American intestines. And most amazingly of all, this genetic cutlery set is a loan. Some gut bacteria have borrowed the seaweed-digesting genes from other microbes living in the coastal oceans. This is the story of how these genes emigrated from the sea into the bowels of Japanese people.<\/p>\n

Within each of our bowels live around a hundred trillion<\/em> microbes<\/a>, whose cells outnumber our own by ten to one. This \u2018gut microbiome<\/a>\u2019 act like an extra organ, helping us to digest molecules in our food that we couldn\u2019t break down ourselves. These include the large carbohydrate molecules found in the plants we eat. But marine algae \u2013 seaweeds \u2013 contain special sulphur-rich carbohydrates that aren\u2019t found on land. Breaking these down is a tough challenge for our partners-in-digestion. The genes and enzymes that they normally use aren\u2019t up to the task.<\/p>\n

Fortunately, bacteria aren\u2019t just limited to the genes that they inherit from their ancestors. They can swap genes between individuals as easily as we humans trade money or gifts. This \u2018horizontal gene transfer<\/a>\u2019 means that bacteria have an entire kingdom of genes, ripe for the borrowing. All they need to do is sidle up to the right donor. And in the world\u2019s oceans, one such donor exists \u2013 a seagoing bacterium called Zobellia galactanivorans<\/a><\/em>.<\/p>\n

Zobellia<\/em> is a seaweed-eater. It lives on, and digests, several species including those used to make nori<\/a>. Nori is an extremely common ingredient in Japanese cuisine, used to garnish dishes and wrap sushi. And when hungry diners wolfed down morsels of these algae, some of them also swallowed marine bacteria. Suddenly, this exotic species was thrust among our own gut residents. As the unlikely partners mingled, they traded genes, including those that allow them to break down the carbohydrates of their marine meals. The gut bacteria suddenly gained the ability to exploit an extra source of energy and those that retained their genetic loans prospered.<\/p>\n

<\/span>This incredible genetic voyage from sea to land was charted by Jan-Hendrik Hehemann<\/a> from the University of Victoria. Hehemann was originally on the hunt for genes that could help bacteria to digest the unique carbohydrates of seaweed, such as porphyran. He had no idea where this quest would eventually lead. Mirjam Czjzek<\/a>, one of the study leaders, said, \u201cThe link to the Japanese human gut bacteria was just a very lucky, opportunistic hit that we clearly had no idea about before starting our project. Like so often in science, chance is a good collaborative fellow!\u201d<\/p>\n

From oceans to bowels<\/strong><\/p>\n

\"Zobellia_journey_seaweed_su\"<\/strong><\/p>\n

Hehemann began with Zobellia<\/em>, whose genome had been recently sequenced. This bacterium turned out to be the proud owner of no fewer than five porphyran-breaking enzymes. This group was entirely new to science, they are all closely related and they clearly originated in marine bacteria. Their unique ability earned them the name of \u2018porphyranases\u2019 and the genes that encode them were named PorA, PorB, PorC and so on.<\/p>\n

They are clearly not alone. Using his quintet as a guide, Hehemann found six more genes with similar abilities. Five of them hailed from the genomes of other marine bacteria \u2013 that was hardly surprising. But the sixth source was a far bigger shock: the human gut bacterium Bacteroides plebeius<\/em>. <\/em>What was an oceanic gene doing in such an unlikely species? Previous studies provided a massive clue. Until then, six strains of B.plebeius <\/em>had been discovered, and all of them came from the bowels of Japanese people.<\/p>\n

Nori is, by far, the most likely source of bacteria with porphyran-digesting genes. It\u2019s the only food that humans eat that contains any porphyrans and until recently, Japanese chefs didn\u2019t cook nori before eating it. Any bacteria that lingered on the green fronds weren\u2019t killed before they could mingle with gut bacteria like B.plebius<\/em>. Ruth <\/em>Ley<\/a>, who works on microbiomes, says, \u201cPeople have been saying that gut microbes can pick up genes from environmental microbes but it\u2019s never been demonstrated as beautifully as in this paper.\u201d<\/p>\n

In fact, B.plebeius <\/em>seems to have a habit of scrounging genes from marine bacteria. Its genome is rife with genes that are more closely related to their counterparts in marine species like Zobellia <\/em>than to those in other gut microbes. All of these borrowed genes do the same thing \u2013 they break down the complex carbohydrates of marine algae.<\/p>\n

To see whether this was a common event, Hehemann screened the gut bacteria of 13 Japanese volunteers for signs of porphyranases. These \u201cgut metagenomes\u201d yielded at least seven potential enzymes that fitted the bill, along with six others from another group with a similar role. On the other hand, Hehemann couldn\u2019t find a single such gene among 18 North Americans. \u201cWe were trying at lunch to think about where you might see patterns this clean,\u201d says Ley. \u201cYou\u2019d have to find another group of people with a very specialised diet. Because this involved seaweed and marine bacteria, it might be one of the cleanest demonstrations you\u2019d get.\u201d<\/p>\n

For now, it\u2019s not clear how long these marine genes have been living inside the bowels of the Japanese. People might only gain the genes after eating lots and lots of sushi but Hehemann has some evidence that they could be passed down from parent to child. One of the people he studied was an unweaned baby girl, who had clearly never eaten a mouthful of sushi in her life. And yet, her gut bacteria had a porphyranase gene, just as her mother\u2019s did. We already known that mums can pass on their microbiomes to their children, so if mummy\u2019s gut bacteria can break down seaweed carbs, then baby\u2019s bugs should also be able to.<\/p>\n

Are we what we eat?<\/strong><\/p>\n

This study is just the beginning. Throughout our history, our diet has changed substantially and every mouthful of new food could have acted as a genetic tasting platter for our gut bacteria to sample. Personally, I\u2019ve been eating sushi for around two years ago and I was intrigued to know if my own intestinal buddies have gained incredible new powers since then. Sadly, Czjzek dispelled my illusions. \u201cToday, sushi is prepared with roasted nori and the chance of making contact with marine bacteria is low,\u201d she said. The project\u2019s other leader, Gurvan Michel, concurs. He notes that of all the gut bacteria from the Japanese volunteers, only B.plebeius <\/em>as acquired the porphyranase enzymes. \u201cThis horizontal gene transfer remains a rare event,\u201d he says.<\/p>\n

Michel also says that for these genes to become permanent fixtures of the B.plebeius <\/em>repertoire, the bacterium would have needed a strong evolutionary pressure to keep them. \u201cDaily access to ingested seaweeds as a carbon source\u201d would have provided such a pressure. My weekly nibbles on highly sterile pieces of sushi probably wouldn\u2019t.<\/p>\n

That\u2019s one question down; there are many to go. How did the advent of agriculture or cooking affect this genetic bonanza? How is the Western style of hyper-hygienic, processed and mass-produced food doing so now? As different styles of cuisines spread all over the globe, will our bacterial passengers also become more genetically uniform?<\/p>\n

The only way to get more answers is to accelerate our efforts to sequence different gut microbiomes. Let\u2019s take a look at those of other human populations, including hunter-gatherers. Let\u2019s peer into fossilised or mummified stool samples left behind by our ancestors. Let\u2019s look inside the intestines of our closest relatives, the great apes. These investigations will tell us more about the intestinal genetic trade that has surely played a big role in our evolution.<\/p>\n

Rob Knight<\/a>, a microbiome researcher from the University of Colorado, agrees. \u201cThis result reinforces the need to conduct a broad and culturally diverse survey of who harbours what microbes. The key to understanding obesity or IBD might well be in genes or microbes acquired under circumstances very different to those we experience in Western society.\u201d Gastronomics, anyone?<\/p>\n

Reference: <\/strong>Nature http:\/\/dx.doi.org\/10.1038\/nature08937<\/a><\/p>\n

Images: <\/strong>nori by Alice Wiegand; sushi chef by Alex Kovach; Zobellia<\/em> by Tristan Barbeyron; seaweed by Mirjam Czjzek<\/p>\n

More on microbiomes: <\/strong><\/p>\n