Microbes Inside You

Invisible you – the human microbiome

We are not alone. Our bodies contain at least as many microbial cells as human ones. These ‘communities’ in and on our person are, in the main, essential.

Home sweet home

There are as many microbial cells in our body as human ones. That makes us human-microbe hybrids. If you took the microbes out of your body, they would weigh about 1.5-2kg (about the same as your brain). Some are just freeloaders and many are useful.

We play host to around 2,000 different types (i.e. species) each living on and in different parts of us. They form extremely dynamic populations, interacting with each other, performing different roles, helping to form us, feed us and protect us and may even affect our mood, weight, intelligence and personality.

Microbes form us

During birth, we are coated with microbes as we pass through the birth canal. These are soon joined by microbes from first touch, first kiss, mother’s skin, mother’s milk, others’ touch, air, clothes, sheets and so on.

These microbes help our newborn bodies work out which cells to make into what, help develop blood capillaries, produce enzymes and digest our food, including our very first meal. During pregnancy, the mother’s microbes shift their net metabolism so that more calories flow from food to her body. Lactobacillus johnsonii, which we pick up in the birth canal and from our mother’s skin and milk, digests our mother’s milk for us (because we can’t). Microbes also help the development of our immune systems. In our first two years it’s a bit of a tradeoff while our immune systems develop and work out how to distinguish the desirable from the non-desirable microbes. Research suggests the microbes themselves have a hand in this.

By the time we are two, and on into adulthood our microbiomes are fully formed –and they have their work cut out.

Microbes feed us

We are a tube with an entrance (mouth) and an exit (anus) so our gut is, biologically speaking … outside our bodies. There are more microbes in the lower gut than anywhere else: about 1,000 different species layered an inch thick. These microbes feed us. They generate around 10% of our energy needs, produce enzymes to digest food, break down tough plant materials and provide vitamins (folic acid, vitamins B and K and nicotinic acid). They regulate fat storage, make essential amino acids (protein building blocks), help us absorb iron among other things and help make new gut cells.

^{This embroidered textile by Rebecca D. Harris represents the human microbiome. Upon this terrain are charted areas of trillions of microbes that live on our bodies, represented as hand-embroidered French knots. It can be found in the Invisible You exhibit, part of the Invisible Worlds exhibition at the Eden Project.}

The microbes in our gut vary from person to person. Malnutrition is not just about what we eat, but what types of microbes we have in our gut. Microbes in the guts of people in vitamin-hungry parts of Malawi can extract more vitamins from food than microbes in the guts of people with vitamin-rich diets in North America. Fat and thin people have different microbial communities too and different diets can change the types they have.

Microbes protect us

Many beneficial microbes stick, stay and protect.

^{Microbes help to keep us healthy}

Gatekeepers: They exclude the unwanted, stand firm and crowd others out. They form skin barriers, cleaning, moisturising and protecting. They colonise and guard the mucus-lined bits at the entrance to the passageways (e.g. up the nose, in the mouth…).

Protectors: They chase and fight off the undesirables and help protect us from auto-immune diseases.

Cleaners: Some microbes detoxify some of the harmful/poisonous things we’ve eaten.

Builders: They help build our ‘immune cell-making factories’ (most of which are in the gut) and help our immune cells reproduce.

Teachers: They help train our immune system in what to accept or reject so they recognise and don’t attack friendly microbes.

Our microbiome is influenced by our ancestry, where we live, who we live and interact with, what we eat and where we go. When we die, our bodies stop working, our immune systems stop working. The microbes take over.