The Hidden Power of Microbes

Begin your study of the oldest and most widespread forms of life on Earth: microbes. Dr. Melissa Booth outlines the course and introduces Lina, the fictional character whose life will be explored from the perspective of the microbes that live in, on, and around her, from birth to adulthood. Learn how the microbes that colonize an infant during its earliest weeks influence long-term health.

Continue your tour of Lina’s microbiome by surveying the five major types of microbes: bacteria, archaea, fungi, protists, and viruses. Examine what they do and where they live in the human body. The statistics are astonishing, since just over half the cells in your body are microbes, comprising some 39 trillion microbial cells versus 30 trillion human cells. Plus, we harbor 380 trillion viruses!

Any part of the human body that has contact with the outside world is a potential homestead site for microbes. But why do our bodies tolerate their presence? Here, you’ll answer the question: What are these microbes doing for you? One of their important jobs is to disarm potentially harmful microorganisms. Discover how they also aid in digesting complex molecules such as gluten.

Follow the steps that transform cacao beans into chocolate as an example of fermentation—an intricate process mediated by different microbes. The ability of certain microorganisms to turn nutrients into energy in the absence of oxygen is what makes fermentation possible. Also, look at wine, cheese, and yogurt production, and consider the health benefits of fermented foods as well as the risks.

Explore the diverse environments of the human gut from a microbe’s point of view: the deadly acidic cauldron of the stomach, the constant antimicrobial rain in the small intestine, and the paradise of nutrients in the colon. Learn how good health depends on microbial fermentations churning away in our bellies. Every gut has its own unique mix of microbe species, but their functions are the same.

Microbes are known to make creatures do strange things, such as zombie ants that climb to a specific height to die and spread the infecting agent. Rabies is another example since it alters animal behavior to promote spread of the virus. Dr. Booth investigates whether microbes within us may hijack our minds for their own benefit. Discover that one line of defense is the blood-brain barrier.

Return to our fictional microbe host, Lina, who is now a toddler living in a rural setting. Compare her microbiome with that of her urban cousin, noting differences depending on pets, farm animals, siblings, playmates, and other factors. Evaluate the connection between allergies and exposure to different microbes. Also, consider the best diet to promote a healthy assortment of microorganisms.

Dig deeper into how microbes and hosts establish their symbiotic relationships, and how the human partnership with microbes can sometimes lead to chronic diseases. Find that some insects and animals have no microbiome at all. What they have instead is a readily digestible diet, with little or no assistance required from microorganisms. Dr. Booth also cautions against microbiome miracle cures.

The amazing adaptability of some microbes can create problems for us. A child’s earache is a good example, resulting from the changed environment in the narrow inner ear canal during a cold, transforming harmless or even beneficial microbes into troublemakers. Turn back the clock to the origin of life on Earth to see how microbes have evolved to flourish under the most punishing circumstances.

Cover the incessant war among microbes, which can lead to collateral damage in humans. Look at cases of competitive exclusion, and tactics such as frontal assault, chemotaxis, chemical weapons, and coordinated and even suicidal attacks—all in the struggle to stay on top. The array of strategies underscores the intricate relationship between the ecology of microbes and human health.

Microbes can be vicious competitors, but very often the fittest microbes aren’t the fastest or the toughest but the most cooperative. Explore the many forms of teamwork displayed by microorganisms. Discover that our multicellular ancestors must have been the outcome of a team effort of different microbes banding together and specializing to navigate the environment.

From the Black Death to COVID-19, humans are vulnerable to zoonotic diseases—those that are commonly transferred from animal reservoirs. Survey a range of these illnesses, including influenza, Lyme disease, leprosy, and various historical plagues. Zero in on the different mechanisms of pathogenesis, or the way a microbe that may otherwise be harmless attacks the body’s tissues, often lethally.

Ancient records show that physicians occasionally argued that invisible particles caused disease, but they were either ridiculed or ignored. With the invention of the microscope in the 1600s microbes were finally observed. However, not until the 1800s were they conclusively linked to scourges such as puerperal fever and tuberculosis. Trace the milestones in this medical detective story.

Catch up with Lina, whose young friend Sam has contracted an infection that won’t respond to antibiotics. This plight is increasingly common as decades of overuse of antibiotics has led to the evolution of resistance in many disease-causing bacteria. Are we entering the post-antibiotic era, when, once again, healthy people can be maimed or killed by minor injuries or common infections?

People generally think of viruses as the enemy, but these microbes play a much broader and often beneficial role in ecosystems. For example, bacteriophages, or phages, are viruses that infect and kill specific types of bacteria. For some antibiotic-resistant infections, a specially targeted phage may be the best hope for a cure. Learn about the discovery of phages and their subsequent history.

Chart the history of vaccines, from traditional practices that protected against smallpox (although at the time no one knew why they worked) to today’s wide array of precision immunizations. Learn how vaccines stimulate the immune system to recognize and fight specific microbes and consider why Dr. Booth would like to retire the term “pathogen,” which stigmatizes some microbes as being bad.

The most life-threatening environments on, above, and below Earth typically harbor microbes that evolved to survive the harsh conditions. From the stratosphere to the ocean bottom to deep underground, microorganisms are truly everywhere. Probe some of the strategies they use to outwit extremes of temperature, pressure, salinity, pH, and radiation. They’re not called “extremophiles” for nothing!

A drop of seawater contains about a million cells, each playing a vital role in planetary nutrient cycles and oxygen production. Investigate the evolution of marine microbes and their crucial roles within the biosphere. As a dominant force in biology, they rival only humans. Reflect on the effects of rising atmospheric carbon dioxide on marine life and the repercussions for terrestrial life.

Soil microbes are a key link in the planetary cycling of nitrogen, carbon, sulfur, and phosphorus—all essential for life. Dig through the topsoil down to bedrock to assess the types of microbial life and their roles in breaking down organic matter, making nitrogen available for plant growth, and enhancing soil structure. Examine the development of nitrogen fertilizers and their ecological impact.

Plants and microbes have been interacting and co-evolving for millions of years. Learn how every plant you see hosts an enormous diversity of microbes from root to leaf tip, improving the health of their hosts through enriched nutrition and protection from aggressive microbes. Also, look at probiotics in agriculture. As discussed earlier, they should always be used with caution.

Is there life beyond Earth? Could extraterrestrial microbes have seeded life on our planet? And what is life, anyway? Address these questions, drawing on research into the survivability of microorganisms in space and the habitability of different regions of the solar system. Zero in on the most promising candidates, among them Mars, the moons Europa and Enceladus, and the atmosphere of Venus.

You’ve heard of global efforts to save the whales, the pandas, the rainforest, and other endangered members of the biosphere. But who is speaking up for microbes? Consider what a microbe-free world would be like and whether the planet is heading inexorably in that direction. The “boy in the bubble” and germ-free mice give an inkling of the problems such a scenario would trigger.

Who would have guessed that a single-celled organism could generate electricity? Or build an internal magnetic GPS? Researchers are documenting an ever-growing list of the powers of microbes, inspiring biomedical and biotechnological innovations that have the potential to improve the lives of everyone. Explore the promise of microbial cancer killers, pharmaceutical factories, and power stations.

Our heroine Lina is now an adult, working in bioremediation to clean up water pollution. Bioremediation is a natural process that uses living organisms to degrade contaminants, and it is one of several applications of microbes covered here. See how the solution to sustainable agriculture, alternative food sources, climate change, and other daunting problems might just be microbes.