Microbiome Overview

1. What is a Microbe?

A microbe is quite simply a microscopic organism. Microbes can be single-celled or comprise clusters of cells. They even include very small animals and other multicellular organisms; many are colonial and assume forms in nature that are easily visible to the naked eye. Microbes can be classified into four discrete groups.

  1. Bacteria are single-celled microbes whose DNA is not bounded by a nuclear membrane.

  2. Archaea are also single-celled microbes superficially similar to bacteria, but their genes reveal them to be distinct organisms. Archaea are the source of many genes found in animals.

  3. Eukarya are organisms distinguished by complex cells having a membrane-bound nucleus and organelles, like mitochondria. Eukarya include not only microbes, but also larger animals plants and fungi.

  4. Viruses are infectious microbes that reproduce only inside living cells. Many scientists debate whether viruses should be considered living organisms or not.

2. Change-Makers Through Time

Microbes living across our planet are the foundation of the entire global ecosystem. They were also the first organisms to evolve on a tumultuous infant Earth, a world that we would not recognize today. Its surface and atmosphere would have been inhospitable to nearly all life as we know it. As these early microbes evolved and diversified, their activities transformed the planet’s environment and laid the groundwork for the evolution of new life, including multicellular organisms like fungi, plants and animals.

Microbial life is orders of magnitude more diverse and abundant than the multitude of organisms we see around us every day. Scientists estimate that there may be a trillion or more species of bacteria, archaea, microbial eukaryotes and viruses -- all smaller than can be discerned by the naked eye. Humans and other large animals are the oddities in a world teeming with microbial life, and the truth is, we owe our very existence to their success. Single-celled, microscopic organisms were the first living things to emerge from the environment of the early Earth, and their activity transformed it. These miniscule pioneers expanded their reach, diversified and evolved, igniting a new course of escalating complexity with the biosphere. Over time, unicellular microbes developed new strategies for living and working together. Out of this cooperation and over several billion years, life became increasingly complex, leading to the evolution of plants and animals.

3. Skin Microbiome

Bacteria, fungi and other microorganisms reside in the upper, or superficial, layers of skin, as well as on hair follicles. They survive on dead skin and oily secretions shed by healthy tissue. Skin has evolved to support a diversity of microbes, which outcompete pathogens, preventing them from entering the body and causing disease.

4. Bodily Microbiomes

Skin, hair, feathers, or scales -- what covers the outside of the animal body is a complex ecosystem for microbes. Our skin is our latest organ, covering the entirety of our body’s surface, protecting what lies within from unwanted intruders, which it does with some assistance from the microbial life that resides on it. As an animal moves through its environment, it is constantly picking up and shedding microbes. Most of these organisms are harmless, or offer some benefit to their host, and are rarely pathogenic. The healthiest animals are typically covered by a great diversity of microbes, which are constantly competing, keeping each other’s populations in check.