IMAGE: THE HUMAN MICROBIOME MAY PLAY A ROLE IN EVERYTHING FROM OBESITY TO ASTHMA (FLICKR/PACIFIC NORTHWEST NATIONAL LABORATORY)
What is it that makes you, you? While you’re made up of 10 trillion human cells, 100 trillion microbial cells also live on you and in you. This vast array of microscopic bugs may be your defining feature, and scientists around the world are racing to find out more. Amanda Smith reports.
Microbes, it seems, are the next big thing. Around the world, scientists are researching the human microbiome—the genes of our microbes—in the hope of unlocking quite a different way to understand sickness and health.
At the Microbiome Initiative at the University of California, San Diego, Rob Knight runs the American Gut Project, a citizen science initiative where you can get your microbiome sequenced.
Breast milk is meant to present the baby with a manageable dose of everything in the environment. It samples the entire environment—everything the mother eats, breathes, touches.
MAUREEN MINCHIN, AUTHOR OF MILK MATTERS.
‘What we can do right now is put you on this microbial map, where we can compare your microbes to the microbes of thousands of other people we’ve already looked at,’ he says. ‘But what we need to do is develop more of a microbial GPS that doesn’t just tell you where you are, but tells you where you want to go and what you need to do, step by step, in order to get there.’
The Australian Centre for Ecogenomics is also setting up a service where you can get your gut microbes analysed. The centre’s director, Phillip Hugenholtz, predicts that in years to come such a process will be a diagnostic procedure when you go to the doctor, much like getting a blood test.
‘I definitely think that’s going to become a standard part of your personalised medicine’, he says. ‘Micro-organisms are sometimes a very good early indicator of things occurring in your body and so it will become something that you’d go and get done maybe once or twice a year to see what’s going on.’
While this level of interest in the microbiome is new, the first person to realise we’re all teeming with micro-organisms was Dutchman Anton Leeuwenhoek, way back in 1676. Leeuwenhoek was interested in making lenses, and constructed himself a microscope.
‘He was looking at the scum from his teeth, and was amazed to see in this scraped-off plaque from inside his own mouth what he called hundreds of different “animalcules swimming a-prettily”,’ says Tim Spector, professor of genetic epidemiology at Kings College London.
‘He was the first to describe this, and it took hundreds of years before people actually believed that we were completely full of these microbes and we’d co-evolved with them.’
Microbes have come a long way over the last century. Until recent advances in DNA sequencing, all tummy bugs were considered bad.
‘We used to think that there was no such thing as a good microbe in our guts, that they were all out to do us no good, and we’ve basically spent the last 100 years trying to eliminate them with disinfectants and then the last 50 years with antibiotics,’ says Spector.
This has given rise to the ‘hygiene hypothesis’, which contends that by keeping ourselves too clean, we’re denying ourselves the microbes necessary to keep our immune system balanced, resulting in all sorts of chronic diseases.
‘Over the last half-century, as infectious diseases like polio and measles and hepatitis and so-on have plummeted in their frequency, chronic diseases—everything from obesity to diabetes to inflammatory bowel disease—have been skyrocketing,’ says the Microbiome Initiative’s Rob Knight.
‘So the idea is that potentially without exposure to a diverse range of healthy microbes our immune systems might be going into overdrive and attacking our own cells, or overreacting to harmless things we find in the environment.’
IMAGE: ANTONIE VAN LEEUWENHOEK WAS THE FIRST MICROBIOLOGIST AND THE FIRST TO OBSERVE MICRO-ORGANISMS USING A MICROSCOPE. (LICENSED UNDER PUBLIC DOMAIN VIA COMMONS)
In terms of human DNA, we’re all 99.99 per cent identical. However our microbial profiles can differ enormously. We might share just 10 per cent of our dominant microbial species with others.
According to Knight, some of the differences are explained by method of birth.
‘If you come out the regular way you get coated with microbes as you’re passing through your mother’s birth canal,’ he says.
Babies delivered by Caesarian section, on the other hand, have microbes that are mostly found on adult skin, from being touched by different doctors and nurses.
‘One thing that’s potentially interesting about that is differences between C-section and vaginally delivered babies have been reported: higher rates in C-section babies of asthma, allergies, atopic disease, even obesity. All of those have been linked to the microbiome now.’
Also important to the development of healthy microbiota in babies is breastfeeding, according to Maureen Minchin, the author of Milk Matters.
‘We’ve known for over 100 years that breast milk and formula result in very, very different gut flora in babies, but it’s only very recently that anyone has thought to look and see what breast milk does contain, and at last count there were well over 700 species of bacteria in breast milk,’ she says.
According to Minchin, breastfeeding is the bridge between the womb and the world for babies.
‘Breast milk is meant to present the baby with a manageable dose of everything in the environment. It samples the entire environment—everything the mother eats, breathes, touches. Her microbiome is present in that breast milk and will help create the appropriate microbiome in the baby.’
Minchin is an advocate of the World Health Organisation’s recommendation to breastfeed exclusively to six months and then continue breastfeeding while introducing other foods through the first and second year.
Related: Why the digestive system and its bacteria are a ‘second brain’
So if what babies are fed is important for their microbiome, what about adults? Tim Spector says research into microbes is yielding new information about healthy eating.
‘It’s going to soon revolutionise how we look at food and diet. This is one of the most exciting things in science at the moment, because it’s obviously much easier to change your microbes than it is to change your genes.’
‘Most processed foods only contain about five ingredients, and in a way our epidemic of the last 30 years of obesity and allergy is that our diets have become less and less diverse.’
According to Spector, studies of people with various chronic diseases, obesity and diabetes show a common feature, which is that their gut microbes have a much-reduced diversity compared to healthy people.
He likes to use the analogy of a garden: ‘A neglected garden has very few species, not much fertilised soil, and this allows weeds to take over in great numbers,’ he says.
‘I think this is a nice concept because we’re very good gardeners, humans, and I think we need to start using those principles—fertilising, adding soil, experimenting and avoiding adding nasty toxins to our own bodies as we would our gardens.’
May your gut flora bloom!