I Contain Multitudes: The Microbes Within Us and a Grander View of Life

I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong dives into the wonderful and often misunderstood field of microbiology. Yong unravels discoveries and knock down conspiracies — all while talking about microbes! I have to say that this is the most fascinating book I have read so far this year.

The myriad microbes in our bodies are collectively known as the microbiome or microbiota. Microbes are a big part of our lives. According to Yong, our oxygen is produced by photosynthetic microbes in the ocean and the bacteria in chloroplasts (we would not be here without them!). Though most cast microbes as antagonists, “[t]here are fewer than 100 species of bacteria that cause infectious diseases in humans”(11). Our microbes also supplement our body cells. It carries a whopping 500 times more genes than your cells. What your body cells cannot do, your microbes are most likely capable of.

We then dive into a crash course on microbiology’s history. While looking through his microscope, the famous lens maker, Antony van Leeuwenhoek, found vast populations of microbes which he christened “animalcules.” The field of microbiology made no significant advances until the nineteenth century, when Louis Pasteur proposed that microbes could be the agents of disease. Before then, disease was thought to be “caused by bad air, or miasma, released from rotting matter”(32). Another breakthrough was seen when Joseph Lister introduced the use of antiseptic for medical purposes. The classification of microbes was enhanced by Carl Woese. In different bacterial samples, he found a common molecule called 16S rRNA. A discovery was made when Woese studied methanogens: “when he looked at its 16S rRNA, he realized it was decidedly un-bacterial”(41). The methanogens were later reclassified as archaea. What marked this as a monumental step for biology in general was Woese’s method of “comparing genes to work out how species are related to each other”(41). This opened the path to metagenomics. Later scientist were able to “extract the DNA from all local microbes, cut it into small fragments, and sequence them together”(43).

According to tests done on sterilized mice, “microbes activated a wide range of mouse genes” and “told them how to use their own genes to make a healthy gut”(54). Microbes also “stimulate the production of pro-inflammatory cells, while others induce dove-like anti-inflammatory cells … they allow us to react to threats without overreacting”(64). Without this equilibrium, we would not be able to respond to harmful threats while overreacting to harmless one. Yong notes the irony of this. While many think of our immune system as a defense that destroys microbes, “microbes craft and tune our immune system in the first place!”(64). When research showed that microbes affect the brain and behavior, scientists experimented on sterilized mice and “by swapping the bacteria in the animal’s guts … also swapped part of their personalities”(72). Microbes even release a chemical called dopamine, which inhibits satisfaction. By releasing dopamine when you eat certain foods, microbes can potentially hone your diet to benefit them.

Sadly, our little friends can turn on us sometimes. Many viruses actually control the microbes in your body which have gone rogue. These are called microphages: “When they touch down on a bacterium, they inject their DNA and turn the microbes into a factory for making more phages”(89). Our immune system helps us control our microbes: “It’s more about balance and good management than defence and destruction”(91).

Yong describes our immune system as an “immunostat.” When relaxed, it can encourage invasions from outside microbes. When intensified, the immune system attacks harmless microbes and cause inflammation. With our modern sanitation, Yong claims that we have tuned our “immunostats” to be set toward the latter. This inadvertently induces problems such as allergies. The lack of fiber in modern diets also affect our intense “immunostat.” When microbes break down bacteria, a chemical called short fatty acid (SCFA) is produced. These galvanize an increase in our anti-inflammatory cells. Fibers also encourage the colonization of helpful microbes with certain digestive enzymes. Our modern world has “cut off routes by which microbes reach us, and then starve those that make it”(125). We then use the microbes’ own weaponry, antibiotics, to kill both harmful and helpful microbes. Without a healthy microbiome, many pathogens can easily penetrate our body. But Yong does not suggest that antibiotics never be utilized; instead, he warns of their overuse which “disrupts our microbiome and foments the rise of antibiotic-resistant bacteria”(128).

Microbes also utilize the special power of horizontal gene transfers (HGTs). All microbes are able to transmit genes to one another. There is a scary aspect to this. Microbes with mutations that allow them to be resistant to antibiotics can transfer its genes to other microbes, making them antibiotic-resistant. Yong describes this as “one of the greatest public health threats of the twenty-first century”(192). But, as with all things, we can harness HGT for our benefit. Yong illustrates this through nori. Nori, which contains special carbohydrates, cannot be digested by regular enzymes. But marine Zobellia can digest it! When nori was eaten raw, Zobellia found on the nori was also eaten. As the Zobellia passed through the gut, it transferred its genes to other microbes. This is why many Japanese are able to digest nori. So hypothetically, if we need some benefit a microbe has, we just need it to pass through our body and allow it to carry out HGT.

Yong imagines an à la carte future , where scientists can equip microbes with specific genes. Scientists could program the microbes to eliminate certain harmful substances. This is the wonderful future of synthetic biology:

Synthetic biologist aren’t limited to sending microbes after pathogens. They might also train their creations to eliminate cancer cells or convert toxins into medicines. (239) In this book, Yong takes readers on a captivating ride through the history and application of microbiology. It contains compelling anecdotes which are sprinkled with a topping of information. For readers interested in how microbes affect our lives, Ed Yong’s I Contain Multitudes is the book to devour.