Our bodies are bustling ecosystems, teeming with trillions of microscopic organisms. This vast, invisible world within and on us has countless inhabitants interacting with each other and their surroundings. Understanding this hidden dimension of life is reshaping how we view human health, revealing that we are superorganisms composed of both human and microbial cells.
Defining the Microbiome
The term “microbiome” refers to the entire habitat of microorganisms in a particular environment. It is a comprehensive concept that includes the community of microbes, their collective genetic material, and the immediate environment they occupy. This ecosystem is populated by a diverse range of microorganisms, including bacteria, archaea, fungi, and viruses.
The microbiome is not a static entity. Its composition and activity are in constant flux, influenced by both internal and external factors like diet and medication. This dynamic nature means the microbiome is a key interface between our bodies and the world around us, constantly adapting and responding to new conditions.
Microbiome vs. Microbiota
The terms “microbiome” and “microbiota” are often used interchangeably, but they have distinct meanings. “Microbiota” refers specifically to the population of living microorganisms themselves—the actual collection of bacteria, archaea, fungi, and viruses in a specific location.
The “microbiome” encompasses the microbiota and their entire theater of activity. This includes the collective genomes of all the microbes, their structural components, and the metabolites they produce. It also covers the environmental conditions of the habitat itself, such as nutrient availability, pH, and temperature.
A useful analogy is to think of an aquarium. The microbiota would be the fish, snails, and shrimp—the living creatures within the tank. The microbiome, in contrast, is the entire aquarium system. It includes the fish (microbiota), but also the water, the gravel, the plants, and all the chemical interactions and nutrient cycles happening within that contained world.
The Human Microbiome
Humans are colonized by a vast number of microorganisms, with non-human cells roughly equaling the number of human cells in the body. These communities are not uniformly distributed, forming distinct microbiomes in different locations, each with a unique composition. Major sites for these communities include the gut, skin, mouth, and nasal passages.
The gut microbiome is the most well-known, containing a dense population of microbes that aid in digestion. The skin hosts a complex microbiome that helps break down lipids to produce natural moisturizers, while the oral cavity and respiratory tract have their own specialized communities. The diversity between these sites can be significant, as the microbial differences between the gut and mouth are comparable to those between soil and oceans.
A person’s core microbiome is established within the first few years of life, influenced by factors from birth and early environmental exposures. While this foundational community remains relatively stable, its composition can change over time.
Why the Microbiome Matters
These microbial communities are not passive residents; they actively participate in fundamental bodily processes. They help protect us from disease-causing pathogens by occupying space and resources, a process known as colonization resistance.
These communities play a part in the development and function of our immune system. Exposure to a diverse range of microbes early in life helps train the immune system to distinguish between friend and foe. In the digestive system, gut microbes are indispensable for breaking down complex carbohydrates and other components of food that our own cells cannot, enabling us to extract more energy and nutrients from our diet.