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# 1 What are microbiomes?

Humans live in a variety of environments, such as cities, deserts, river deltas and mountain tops. Humans also live alongside a wide variety of animals and plants, eat a large variety of foods, and travel to diverse environments. Microorganisms, also known as microbes, can be found in all these environments alongside humans. Microorganisms are usually single-celled (for example, bacteria) or multi-celled (such as some fungi) that can only be seen through a microscope.

The warm core temperature of the human body and resource-rich internal environment makes the human body optimal for the growth and maintenance of the body’s own cells. However, it also means that this is an ideal environment for the growth and survival of some microorganisms.

The vast majority of microorganisms that humans encounter on a daily basis are harmless. However, some microorganisms can invade the body and use resources at a cost to the human host, or excrete damaging waste products and toxins, all of which can cause disease or even death. These microorganisms are called pathogens and are potentially disease-causing microorganisms. Pathogen is a broad term that encompasses different types of microorganisms, including bacteria, viruses, fungi, protozoa and parasites. Some molecules are disease-causing too, such as toxins and prions. However, some microorganisms can actually be beneficial to humans, and these are known as symbionts, and this includes the microorganisms of the microbiome.

Often, the terms microorganisms, microbiota and microbiome are used interchangeably, which can be confusing. However, they have all have slightly different meanings and this is shown in Figure 3.

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Figure 3 The difference between microorganisms, microbiota and microbiome

The key difference is that the microbiota refers purely to the collective group of organisms living within a specific environment, such as the gut. So, the gut microbiota is all of the bacteria, fungi, viruses, etc, that are found within the gut.

## Fun fact: tricky terminology

Scientific terminology can sometimes be challenging! The words often seem very long and complicated. To help understand them, it can be useful to break the words down into smaller parts. For example, microbiome can be broken down as follows:

- micro- derived from the Greek words for ‘small’ or ‘tiny’
- -biota also has Greek origins, relating to ‘life’
- -biome translates as ‘the root of life’ and also meaning ‘community, area or environment’.

So, microbiota refers to the small living microorganisms in their specific environment. The microbiome refers to the environment and the microbiota and their genetic make-up and all the substances they produce to interact to form a community.

- Question 1

  Thinking about a specific type of microorganism mentioned earlier, can you use the information above to deduce what the word ‘viriome’ means?

- This word can be broken down into ‘viri’ which relates to viruses, and ‘ome’ which, as you learnt above, means ‘community or environment’. So a viriome of an environment is the total virus content within it.

The microbiome includes the microbiota but also includes other elements, such as structural components, the metabolites (substances produced by the microbiota) and the environmental conditions themselves, such as the wall of the gut and substances it produces.

The gut microbiome is highly dynamic, with constant interaction between the human cells, the microorganisms of the gut microbiota, and the substances they produce. The microorganisms of the gut microbiota even interact and influence the behaviour of each other! You’ll learn more about this shortly.

◄Contents►Next: 1.1 Overview of the gut microbiome

OpenLearn - The gut microbiome – balancing the body
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