Has I Contain Multitudes by Ed Yong been sitting on your reading list? Pick up the key ideas in the book with this quick summary. When you hear the words “microbe” and “bacteria,” what comes to mind? You might picture them as “those lousy little beasts that, every year, steal days of your life by attacking your health and forcing you to stay in bed and drink chamomile tea – yuck!” Did you know, though, that microbes like bacteria are actually the reason our immune systems function at all? Indeed, microbes are vital to the entirety of our bodily functions – and the human body contains more of them than actual body cells. This book summary will help you learn to welcome your microbes and appreciate them as your body’s little helpers. You’ll discover the exceptional role that microbes have played in our evolution and why it is that to hang out with microbes is to be in good company – not only for us, but for all organisms. In this summary of I Contain Multitudes by Ed Yong, you’ll also learn

• how many microbes fit on the head of a pin;
• that microbes make a fish invisible; and
• why some of the leaves on apple trees don’t turn yellow in fall.

I Contain Multitudes Key Idea #1: Microbes are everywhere, and they help our planet function.

Microbes have existed on earth for so long that humans can hardly comprehend it, so let’s examine it another way: if the Earth’s 4.5 billion years of existence were one calendar year, humans would have shown up in the last 30 minutes of December 31st, five days after the extinction of the dinosaurs. Microbes, on the other hand, would have been around since March. That’s a long time ago, and for a while they were the only living things around. But even back then, they were hard at work, shaping the planet we know today. The term “microbes” is actually in reference to a wide array of tiny single-cell organisms, which includes various species of bacteria and fungi. Just how tiny are they? Microbes are actually so small that a million of them can actually fit on the head of a pin. But, their size doesn’t equal their role. Microbes are always busy doing things like breaking down various molecules around us. This is how soil is able to get enriched with all sorts of good stuff, and nutrients such as carbon and oxygen are able to complete their environmental cycles. Microbes also played a crucial role in creating Earth’s atmosphere. Microbes were the first living thing on Earth to use photosynthesis, which is when an organism uses energy from sunlight to turn carbon dioxide into water and sugar — food! They then eat this sugar, which allows them to release oxygen, thus creating our atmosphere in the process. This also set the foundations for the carbon cycle, without which, life couldn’t exist. This is the absorption of carbon dioxide by plants, the consumption of plants by animals, and the exhalation of carbon dioxide by animals. Another reason microbes are so amazing is because of their ability to adapt to just about any environment. You’ll find them everywhere: in the ice of Antarctica, up among the clouds, and even down at the edge of an underwater volcano, where the temperature reaches 400° C. Microbes are able to adapt to these extreme environments due to the fact that they can evolve at an extremely rapid rate. By forming a physical link from one cell to another, pieces of DNA can be sent and added to a genome. This means that microbes can share an adaptation from their neighbor, and pass on new genes during reproduction, which can make evolution happen much faster than simply through natural selection.

I Contain Multitudes Key Idea #2: Along with our own genes, everybody also has microbial genes, which influence our lives and development.

If you happen to be a fan of scientific journals, you might have read that for every human cell, there are actually ten microbial cells living within our bodies. While this is actually an exaggeration, the truth is still impressive. It turns out, microbes do make up the majority of the cells and genes in our body. We have around 69 trillion cells in our body, and over half of them — around 39 trillion — are microbial. There are also around 20,000 genes in the human genome, but if we were to include all of the microbial genes we carry, the number would become 500 times bigger. Every individual, regardless of the species, has unique and complex microbial communities called a microbiome. This means that every part of the body has its own community, and although each person’s microbes are different, these communities are there to perform the same function for everyone. A microbiome is like any other natural ecosystem: each community has a certain microbe that acts like a dominant leader, making sure things function properly. For example, certain microbes work to balance the levels of acidity in its particular part of the body. This is why the health and development of all animals and humans depend on microbes. This is especially true for our immune system. Breast milk is rich in over 200 nutrients, including human milk oligosaccharides, or HMOs. The thing is, babies can’t digest HMOs. They’re actually only there to feed a special microbe in our gut called B. infantis. When this microbe digests HMOs, it releases nutrients in the form of proteins, which babies can digest. Among these proteins is an anti inflammatory protein that coats the gut, which can help calibrate our immune system. The gut microbes of humans and animals serve many functions. For instance, mice have a family of gut microbes called Bacteroides thetaiotaomicron. This microbial family activates certain genes while the mice are developing to ensure that they form the right blood vessels and that their guts will have the right microbes to help break down toxins and build nutrients throughout their lives.

I Contain Multitudes Key Idea #3: Symbiosis with microbes gives some animals remarkable powers.

In many parts of the Northern Hemisphere, when autumn arrives, a tree’s leaves will turn to beautiful shades of yellow, orange, and red. The thing is, if you look closely, you might notice that some leaves actually stay bright green. As it turns out, this happens because of one of the many remarkable relationships between microbes and animals. In this case, it’s a partnership between the tentiform leafminer moth and Wolbachia, the world's most common microbe. Since the leafminer matures through the formation of a cocoon on a tree’s leaf. It contains a microbe that will produce a hormone to ensure that the leaf stays green and doesn’t fall down prematurely, which would kill the moth. Another fascinating relationship involves a little cephalopod called the bobtail squid and a highly complex system of microbes that creates a light-emitting organ to keep it safe at night. This microbial cocktail works by making the squid’s outer layer of cells hospitable to only one particular microbe. And when these microbes arrive, they’re supplied with nutrients that will help them to actually become one with the squid. Remarkably, these microbes then act as the squid’s defense system, producing a glow that matches the sky’s moonlight, effectively hiding it from any hunters lurking below. Since they have no silhouette or discernable shadow, the bobtail squid appears virtually invisible to predators. While these are particularly extraordinary examples, it turns out, helpful microbes aren’t as unusual as you might think. In fact, they’re actually the rule, rather than the exception. Since microbes can survive in just about any environment, they’re also able to help animals digest otherwise indigestible food — they’re the animal kingdom’s universal helpers. Between ten and twenty percent of all insects depend on microbes to provide then with vitamins and help them build cells and proteins. For reference, half of a termite’s body weight is made up of helper microbes that are devoted to digesting cellulose. As we’ve seen, microbes are crucial to survival, so it’s imperative that they’re passed on to offspring. For example, a type of Japanese stink bug does this by coating her eggs in a special fluid containing essential microbes. Then, when her babies hatch, they have a microbe-rich first meal waiting for them. This is very similar to the important microbes we receive from our mother’s milk.

I Contain Multitudes Key Idea #4: Alliances with microbes need careful balance.

Despite how helpful millions of microbes can be, as well as the fact that there are only around one hundred microbes that can actually harm us, there’s still a huge market for antibacterial cleaning products. In fact, there really isn’t such a thing as a “good” or “bad” microbe; it’s all dependent on the environment the microbe is in. For example, there are millions of different microbes that make their homes in our gut to help us digest food. The thing is, if these same microbes got onto our skin, they could actually infect a wound and cause all sorts of problems. As it turns out, farmers actually take advantage of this fact, which prompts them to use the microbe Bacillus thuringiensis as a pesticide. When this microbe comes into contact with a caterpillar, it punches holes in the insect’s stomach. It then releases gut bacteria into the caterpillar’s bloodstream. Naturally, the insect’s immune system goes into shock, thus killing it through inflammation. Because of this, the right barriers need to be put in place, because barrier will help microbes stay in their proper, enclosed environment. Insects do this with the help of special cells called bacteriocytes. This helps hide the microbes from the immune system, fencing them in with harmful enzymes and antibacterial chemicals, while also ensuring the microbes get their necessary nutrients. The problem is, for larger and more complex animals, it gets far more complicated. For us humans, our microbes live around our organs, rather than in them, but the human body helps to ensure that only the helpful microbes are invited by setting the right conditions. Our guts are full of powerful acids, which make for a unique environment only suitable for a select few bacteria. Another common means of defense for most vertebrates is mucus. Mucus carries bacteriophages: domesticated viruses that actually feast on microbes that can cause us harm. Last but not least, we have our immune systems, which produce white blood cells that function as a type of bodily border patrol, capturing any unwelcome microbes that sneak through. When an emergency comes up, this same immune system will ensure that antibodies are built and other countermeasures are prepared.

I Contain Multitudes Key Idea #5: A healthy body and immune system depends on a diverse microbiome.

Many of us know at least one germaphobe, or perhaps someone with strong opinions about hygiene. However, if you really want a healthy body, there are some essential facts you should know. To stay healthy, your immune system needs to be properly tuned – like a thermostat – to the ideal setting. Otherwise, your “immunostat” could be too low, meaning that it only reacts to major threats, rather than taking the smaller ones into account as well. When our immune systems are set like this, they may completely ignore a threat that may turn into an infectious disease. On the other hand, your “immunostat” could also be too high, in which case it can be jumpy and overreact by attacking harmless microbes like pollen, or even your own friendly bacteria. If it’s stuck on this setting, you might be at risk of coming down with an allergic disease. However, exposing ourselves to microbes can help us to get our immune systems set on the healthiest setting. The problem is, a modern lifestyle has a tendency to minimize this exposure. Avoiding both infectious diseases and allergic diseases requires that the immune system be set at the proper level early on through exposure to microbes. This is actually something that generally happens early in our childhoods, when we’re exposed to dust, dirt, and mud. The thing is, growing up in an urban environment has caused this to be a less and less common experience over time. When we live in cities, we shower with sanitized water, eat processed foods, and continuously have less contact with domesticated animals. This is due to the pattern that society has supported lately, putting a huge focus on cleanliness. In order for our immune systems to function at its best, it’s crucial that there is some healthy competition; it’s more difficult for bad microbes to make a home in your gut if you have lots of good microbes actively competing for nutrients. It’s possible to prompt this when we work to maintain a diverse diet, as eating this way appeals to many different gut-microbes. Eating a lot of fruits and vegetables is great for this. Plant-based foods are rich in fiber, which is tougher to digest than processed foods, which is something that lots of microbes love and gravitate towards, thus keeping us healthy.

I Contain Multitudes Key Idea #6: Being able to manipulate our microbiomes could be the next step in healthcare.

It’s pretty clear that health advice these days has been simplified. Feeling tired and worn out? Take some vitamins. Have a cold? Take this medicine to kill the virus. The thing is, though, because our microbiomes play such a huge part in our lives, it’s only natural that we should think about manipulating this system if we want to change something in our overall health. This, however, is easier said than done. The problem is, our microbiomes are so large and complex that adding just one kind of microbe to the overall microbiome hardly ever has a noticeable effect. If you’ve started eating probiotic yogurt to help your digestive system, you might find yourself disappointed with the lack of results. This is because yogurt’s microbial cultures are not natural to the gut, so it’s hard for them to make a lasting impact. Introducing a full microbiome, on the other hand, could save lives. RePOOPulate is a project with the goal of helping people to overcome a deadly infectious disease known as Clostridium difficile. This condition comes with symptoms that include fever, nausea, and severe diarrhea. It’s a tough disease to control, but with a healthy stool sample from a relative, doctors are actually able to transplant an entire microbial system into the patient, which can get them well on the path to recovery. In order to create more effective treatments, doctors are also looking into how they might manipulate microbes in a way that will target a specific area of the body. Most treatments, like aspirin or antibiotics, are broad, affecting every cell in the body in the same way. However, there is potential for microbes to be utilized in a more targeted way , with the potential to release specific doses of a medication to a specific site. In 2014, researchers at the Harvard Medical Institute were able to equip an E. coli microbe with a genetic switch that made it turn blue in the presence of antibiotics. Like a microscopic alarm bell, the microbe would allow doctors to see if a patient had taken their medication. This has inspired others to look at new ways to use gene switches. The hope is that modified bacteria could act as an early detection system for diseases and provide a warning before the first symptom even reveals itself.

In Review: I Contain Multitudes Book Summary

The key message in this book: Microbes are everywhere, and for good reason – they’re vital to our well-being! Each species has a distinct community of microbes as well as their own method for of maintaining that partnership over generations. Taking microbes into account, we can view our bodies, and those of the animals around us, as thriving ecosystems rather than just individuals. Looking at things this way opens up many new possibilities for how we might approach and understand our medical and environmental problems.