Humans are multicellular organisms, meaning that they are made up of many cells that interact with each other. Our cells are termed eukaryotic and are mini factories with a control room (the nucleus) that houses the instructions for the cell in the form of genes made up of DNA. All humans share about 99.6% of the same DNA, with the remaining 0.4% giving us our individuality. Our DNA is referred to as our human genome, which is for the most part stable, but some instructions can be altered by environmental factors throughout life. With me so far?
Would it surprise you to know that as you go about life, only one of every ten of your cells is one of these human nucleated eukaryotic cells? The others are blood cells (that lose their nucleus) and some 38 trillion bacteria - tiny, single celled organisms that live on you and in you!
You might be thinking, gross, yuck, no way, or something similar but not to worry, they are so small that although they vastly outnumber our own cells, they only make up 1-3% of our body mass. It also turns out that most bacteria are actually our friend. There are some things that our genes don’t know how to do, and bacteria lend a hand by adding their genes to our complement of biological tools.
The combination of these bacteria, along with some other microorganisms is referred to as our microbiome and is even more unique than our DNA with only about 40% being the same as other people. Apparently, it is possible to tell who has touched which keys on a keyboard from the bacteria that are left behind (another yuck?)!
So where are all these bacteria and where do they come from?
There are four major areas of the body that are colonized by bacteria in somewhat of a symbiotic relationship. We host them and they help us! There are different types of bacteria performing different functions in different places, but largely they are divided between the mouth, the skin, the digestive system or gut and the urogenital system.
It’s thought that in-utero, the environment is sterile, but our microbiome starts to be established at birth. Vaginal delivery kick starts the process, picking up bacteria from the birth canal and this is followed by transfer of beneficial bacteria in breast milk. With C-section births, the first bacteria are more from skin contact, which provides a slightly less diverse population of bacteria – more on bacterial diversity later…… During our first few years of life, environmental factors cultivate what will become our personal microbiome which will set us up with an arsenal of helpers and for the most part, stay with us for life.
What do they help with?
One of the major tasks of gut bacteria is to break down food substances into the molecules we need. It’s thought that gut bacteria can vary widely depending on diet and can (and do) change with our changing diet.
The ability of bacteria to rapidly evolve and swap genes may have also allowed us as humans to spread across the globe and be able to digest new food items as we went.
The wider the diversity of gut bacteria we have, the more different foods we can process, and the better we can incorporate or manipulate nutrients to our needs. Just eating a varied diet isn’t enough – we need the right gut bacteria to break down the components in food and synthesize vitamins.
Beneficial bacteria can neutralize toxins and crowd out pathogenic (disease causing) bacteria and are even involved in training our immune systems. Remember that diversity bit – the more different bacteria a young immune system can be exposed to, the more it learns to differentiate between good and bad bacteria (so let kids play in the mud!). It’s even possible that allergies and autoimmune disorders can be reduced by early exposure to a wide variety of bacteria, so letting Fido be around your baby is ok (so long as Fido is friendly).
Fun facts!
A gut microbiome that is out of balance can lead to anxiety and depression because your gut is linked to your brain via the vagus nerve. Conversely, stress can throw the balance of the gut microbiome off – have you ever felt like throwing up before an exam or an interview?
Your gut bacteria also have their own clock and know when they are supposed to be processing stuff, so jet lag isn’t just to do with sleep – your friendly, helpful gut bacteria need to catch up too. Maybe that’s why travel can lead to so many digestive issues……
Bacteria on your skin can help to dispose of dead skin cells, but also act as a deterrent for harmful bacteria to take up residence, coordinating with your immune system as a first line of defense.
What do antibiotics have to do with all this?
When you are sick (due to a bacterial infection), you may be prescribed antibiotics. Many of these are broad spectrum which means they kill most bacteria – good and bad. You may have heard that you should take probiotics with antibiotics, and this is to try to start to build back your good gut bacteria. Unfortunately I will be needing to put this to the test this week :( Apparently it can help, but it can take up to four years to fully recover your microbiome and in some cases, such as that especially rare bacteria you picked up somewhere, you may never get it back to how it was. Worth thinking about if you are not sure you really need antibiotics (apart from the rise in antibiotic resistance, but that’s another story).
With the advent of various sequencing techniques, much more is being understood about our microbiomes and in time it may be possible to tailor make treatments depending on our individual imbalances. It could also be possible to improve fitness and even reduce the rate of aging by using targeted probiotics.
Lastly, and this one really has an ick factor – if your gut microbiome gets so out of whack that it can’t recover, you could always take a “crapsule”. As the name suggests, this is literally a capsule of crap (freeze dried donor feces) and has been shown to be 90% effective in the treatment of C. diff. that can cause potentially deadly symptoms of fever and diarrhea. Crapsules are even being studied in the treatment of liver cirrhosis, Crohn’s disease and ulcerative colitis among other diseases.
So are we human? I would say that we are resoundingly human, but being human, we utilize tools for our survival, and those tools include not only tools we craft, but organic microorganisms too.
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