Fun with Liquid Nitrogen

Bacteria, man. They’re all over the place. The little single-celled suckers are so tiny you can’t see ‘em, but trust me, they’re there. For one, your skin is covered in bacteria and for two, you’ve got somewhere in the realm of 100 trillion of ‘em inside your digestive tract. That’s somewhere to the order of ten times as many as the number of cells that make up your own body (bacteria are much smaller than most mammalian cells). That translates to something like three pounds of living bacteria you’re carrying around at all times.

So just how important are the little things we give such a bad rap? They’re by far the most diverse and most common form of life on the planet. Prokaryotes – that is, simple cells with no nuclear membrane or other defined cell organelles – are made up of bacteria and their oddball cousins archaea (which we’ll discuss another time since they really deserve their own post). And pretty much everywhere you look? There’s bacteria there. Perhaps as many as 150 million species of bacteria are out there, some with such highly specialized functions that we’re still discovering the extent of the ridiculous ways they manage to survive and even thrive in environments unsuitable for multi-cellular life. In fact, bacteria – or something like them – were probably the first real life on Earth and, all things considered, they’ll probably be the last, too. Stephen Jay Gould went so far as to argue in his book Full House that bacteria are – and always have been – the dominant form of life on the planet and all of us eukaryotes are just along for the ride, ostensibly by the good graces of the bacteria.

The lesson being bacteria are like Danny Tanner in many ways.

It’d be hard to comprehend all at once, then, the manifest ways in which bacteria win at life. So let’s just focus on that squishy several trillion we keep close to our hearts and even closer to our stomachs. Called the gut microbiome – “microbiome” being a fancy word for “the sum total of single-celled organisms in an environment” – along with any of the other non-bacteria single-celled organisms that regularly reside inside of the human GI tract such as the occasional protist, these bacteria are a lot more important than most people give them credit for. After all, it’s pretty darned hard to digest your food unless they’re there, assuming, that is, you don’t live on a diet of sugar-water and reconstituted whey protein. You see, all those complex molecules that make up our food – lipids, enzymes, complex carbohydrates, all the usual suspects – are very hard for our own cells to break down by themselves. They can do it, just not very efficiently. It’s much easier to have them broken down by other, surrogate cells specialized at the task who, in turn, excrete smaller, simpler molecules that our own metabolism is good at handling. This is where our gut flora come in and is part of why newborn babies can only drink milk and not eat solid foods: their gut flora have yet to develop enough to break down the rougher stuff to the point where their digestive systems can handle it.

“But wait!” you think. “My brother-in-law has gotten food poisoning from traveling abroad no fewer than three times! Isn’t it conceivable that regional and cultural dietary variations might also lead to differences in gut microbiomes based on the needs presented by the foods in question?”

And you’d be right. You’d also be me because my brother-in-law has gotten food poisoning no fewer than three times traveling abroad. I give him credit for always being willing to try the local fare, though, for what it’s worth.

The simple answer to that question appears to be yes, there are differences in gut microbiome based on regionally and culturally-dictated food intake. Take sushi for example. Sushi is wrapped in this specially-prepared kind of seaweed called nori in Japan. And, while sushi in the US is almost always made with roasted (and therefore sterilized) nori, back in Japan raw nori was dominantly used to prepare sushi until recent food purity laws went into effect. Now, you might think it would be difficult for the Japanese to gain any sort of nutrition out of raw seaweed, but as it turns out, they’ve got a secret weapon.

And no, it’s not forest fires.

As a group out of France led by Mirjam Czjzek, Gurvan Michel and Jan-Hendrik Hehemann reported in Nature, native Japanese people have a special enzyme in their own gut microbiome unseen in Westerners that specializes in digesting the sulfur-rich (and therefore hard-to-break-down) complex carbohydrates in seaweed. This appears to exist in their own Bacteroides plebeius, a common member of the human gut flora lineup that doesn’t accomplish the same task in other cultures (get it? Cultures? Eh? Eh?) of people. So how did it gain this ability in Japanese?

It seems it got it from a process called horizontal gene transfer in which two bacteria can swap genes through their membranes, a neat little trick that eukaryotic cells – what with their DNA all bound up into chromosomes inside of nuclear membrane – can’t accomplish, or at least not nearly as easily. It’s believed to be an important process driving evolution of single-celled organisms and in this specific case the authors think the gene came from the marine bacterium Zobellia galactanivorans, known to carry the genes necessary to digest these seaweed carbohydrates. And so, inside the guts of Japanese people eating raw nori, Zobellia encountered Bacteroides and the two perfect strangers managed to forge a sort of molecular kinship.

The lesson being bacteria are like Balky in many ways.

This, in turn, was beneficial not only to the Bacteroides but also to the host organism who consumed the raw seaweed and can now gain more nutrients from it. Of course, the authors didn’t find the Zobellia gene in the microbiome of all of the Japanese test subjects, only 5 out of 13 of them (as opposed to 0 of 18 Westerners). This goes to show just how individualized gut microbiomes can be and how this sort of horizontal gene transfer might be going on in thousands if not millions of different instances that allow for each species, group and even individual mammal to digest and gain nutrients from its food in a unique way. The study of the gut microbiome, then, will lead to a better understanding not just of how bacteria work, but of how they interact with our own bodies that they inhabit in a way that contributes to our own individuality.

As for me, I only developed a taste for sushi in my mid-20s and even now I still prefer unrolled sashimi to anything with nori. I could sure go for a burrito, though.

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