By Tom Baker / Japan News Staff WriterI Contain Multitudes: The Microbes Within Us and a Grander View of Life
By Ed Yong
The Bodley Head, 354pp
The tiny, nocturnal Hawaiian bobtail squid has organs filled with a captive population of glowing bacteria. These organs are located on the underside of the golfball-sized creature, allowing it to swim in the moonlit shallows without casting a shadow on the sand. Squid-eating fish are thus less likely to spot it.
It’s common to think of relationships between bacteria and animals as infections. But as British science writer Ed Yong reveals in the endlessly fascinating “I Contain Multitudes,” such relationships are often symbiotic. The squid gets camouflage; the bacteria get a home.
One startling example of such symbiosis involves human breast milk. After lactose and fats, its main ingredients are sugars called human milk oligosaccharides (HMOs). Mothers use a lot of resources and energy to make them. “But babies cannot digest them.”
What can digest HMOs is a bacteria called B. infantis, which “is often the dominant microbe in the guts of breast-fed infants.” According to Yong, it converts HMOs into short-chain fatty acids that directly nourish the baby. B. infantis also helps the baby’s intestines and immune system to develop. This is one bacteria you want your child to have.
While learning about the bacteria within you, you may also enjoy learning the recipe for mucus. It’s “made from giant molecules called mucins, each consisting of a central protein backbone with thousands of sugar molecules branching off from it. These sugars allow individual mucins to become entangled, forming … a Great Wall of Mucus that stops wayward microbes from penetrating deeper into the body.”
In your gut, that mucus wall is a cozy home for quadrillions (yes, quadrillions with a Q) of friendly viruses that nestle into it while waiting to attack unfriendly bacteria.
Much of the book describes how microbes change the lives of non-human animals.
In recent decades, a type of bacteria called Wolbachia has been learned to have an astonishing range of effects on many insect species. There’s a type of wasp whose population turns entirely female in its presence. The insects then reproduce by cloning themselves — unless they are given antibiotics, in which case the bacteria die and males rejoin the population. In a caterpillar that lives inside the leaves of European apple trees, Wolbachia releases a chemical that keeps the leaves green well into the autumn, giving the caterpillars more time to mature. In bedbugs, the germ “makes B-vitamins that are lacking in the blood that the bugs drink.”
Late in the book, we learn that Australian scientists are trying to use Wolbachia to make mosquitos immune to — and thus unable to spread — dengue fever.
Microbes also influence each other. Bacteria, even of different species, sometimes link up and swap DNA. Scientists think this is how a particular gene from a bacteria that lives in the ocean wound up being utilized by otherwise unrelated bacteria in the guts of people in Japan.
What does the gene do? Well, nori seaweed “contains unique carbohydrates that aren’t found in land plants.” The gene in question helps to break those carbohydrates down, making nori more digestible.
Remember that next time you sit down to enjoy some sushi.
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Where to read
On a sofa, cuddling with someone whose microbes you’d like to share. Scientists say that “roommates share more microbes than people who live apart, and couples are even more microbially similar.”Speech