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I Contain Multitudes:

The Microbes Within Us and a Grander View of Life

Ed Yong


WE TEND TO describe our immune systems with military metaphors. Pathogens invade our bodies, knock down our defenses, and try to kill us dead. We fight back with hand sanitizer and mild germ-related panic. Or we go nuclear and blast them with antibiotics. Ed Yong's beautiful, smart, and sometimes shocking new book I Contain Multitudes: The Microbes Within Us and a Grander View of Life will make you take a deep breath.

Yong, a science writer, blogger, tweeter, and TED talk-giver, takes readers from coral reefs to hyena backsides to describe the stunning amount of work bacteria (and viruses too) perform for us humans and for every other thing on Earth. How do Hawaiian bobtail squid get their glow? Germs! Don't care about that squid? You will once you read Yong's description of how luminous bacteria colonize and illuminate it. Here are seven other questions you probably have never thought to ask, but that will be answered anyway in these pages.

What should I think about when I think about the immune system?

For starters, you shouldn’t think about some kind of battle between good and evil. Microbes in your body dial the immune system up and down (so you don't get all infected or go all auto-immune); they cause certain cells to get made; they train it to differentiate good guys from bad guys. 'I think it's more accurate to see the immune system as a team of rangers in charge of a national park - as ecosystem managers,' writes Yong. 'They must carefully control the numbers of resident species, and expel problematic invaders.' Because the immune system isn't a standing army. 'The immune system is't just a means of controlling microbes. It is at least partly controlled by microbes.' They are kind of the boss of you. You need to update your mental metaphor.

What would happen if every germ on Earth suddenly vanished?

All hell would break loose. Animals that eat grass (deer, cows, horses) would starve, since they need germs in their stomachs to digest cellulose. Coral would bleach out. 'In the deep oceans, many worms, shellfish, and other animals rely on bacteria for all of their energy,' Yong writes. 'Without microbes, they too would die, and the entire food webs of these dark abyssal worlds would collapse.' And don't stand there all smug, vegetarians. Microbes make nitrogen, and plants need nitrogen, so there's the rest of the food supply shot. Also, as Yong says, 'microbes are lords of decay.' There would be shit (and rotting leaves and dead bodies) everywhere.

What's so great about mucus?

You guys, mucus—snot, boogers, slime, nose goblins, phlegm—is the best. It’s made of huge molecules that make a big tangle (Yong calls it “a Great Wall of Mucus”) to keep microbes where they belong. And it has a posse. A posse of little guys called phages, which are actually viruses that infect bacteria and kill them. “Imagine hordes upon hordes of them, stuck head-first, their legs outstretched and waiting to embrace passing microbes in a lethal hug,” he writes. One mucus researcher even thinks that creatures might switch up the composition of mucus to attract specific phages so that they kill some bacteria and not others. Woah.

Why do babies have lame sluggish immune systems?

Most people think that babies are prone to infection because their immune systems are dumb and immature. Not so. “To allow our first microbes to colonize our newborn bodies, a special class of immune cells suppresses the rest of the body’s defensive ensemble,” Yong writes. The infant’s immune system is taking a dive so germs can move in and get settled. But of course the baby only wants the best and most friendly germs to come to this little microbial birthday party. Mom to the rescue!

Why do human mothers make 200 types of molecules called oligosaccharides in their breastmilk when babies can't even digest oligosaccharides in the first place?

Look kid, it's not about you. The fats and the lactose in breastmilk, that's for you. Drink up. But those oligosaccharides, those are for microbes, specifically one called Bifidobacterium longum infantis. You really want to attract that that guy and keep him around. Because B. infantis, as Yong writes, earns its keep by eating up those oligosaccharides and spitting out short-chain fatty acids. Baby gut cells eat the fatty acids. In other words, mom is feeding the B. infantis so the B. infantis will feed the baby. Your baby is eating germ poop! This microbe also tells gut cells to make proteins that glue everything together. And it makes anti-inflammatory molecules. It's kind of a big deal. Unfortunately, B. infantis might be an endangered species. In developing countries, up to 90 percent of babies are colonized with the germ. In developed countries, however, that number is around 30 or 40 percent. Scientists aren’t sure why, but it's probably not good.

Is there a bacterium that has a thing for men?

Yes! Here are some things that Wolbachia pipientis can do. It can eliminate the males of a certain wasp species. It can turn guy woodlice into gal woodlice. It kills baby boy butterflies. 'Females are its ticket to the future; males are an evolutionary dead end,' Yong writes. 'So it has evolved many ways of screwing over male hosts to expand its pool of female ones.” Oh, but also? It protects mosquitos from Zika, which means it could be deployed to protect you from Zika. Which goes to show you. 'There is no such thing as a ‘good microbe’ or a ‘bad microbe.’ These terms belong in children's stories. They are ill-suited for describing the messy, fractious, contextual relationships of the natural world. In reality, bacteria exist along a continuum of lifestyles, between 'bad' parasites and 'good' mutualists.'

Are there probiotics for goats?

There was this plant in Australia, and people wanted goats to eat it, but it was poisonous. But goats in Hawaii could eat this same plant. So scientist Raymond Jones, (“After several long flights, some involving thermos flasks full of rank rumen fluids and others involving live goats,”) dosed the Aussie goats with rumen germs from the Aloha goats and presto! They could eat the poisonous plant. Farmers buy Synergistes jonesii as a “probiotic drench” they spray on the critters. Which sounds a little more palatable than a fecal transplant.

Bonus question: Speaking of! What is the worst/best fecal transplant joke in this book?

Well, if you could give people the microbes that live in the poop that seems to help when given to people with Clostridium difficile infections, but not include the actual poop… that would be a stool substitute. It would be (drumroll) a sham-poo.

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