By Tilly Potter, Department of Twin Research, King’s College London
I recently began my PhD during which I will be carrying out investigations into the human microbiome – that is, all of the microbes we harbour on and in our bodies and their genetic material. The reasons why I was attracted to this area are likely similar to those of other scientists who have entered this field; microbiome research is still in its relative infancy yet appears to hold enormous potential regarding understanding differences between health and disease, with the number of diseases or adverse health states examined continuing to increase with time. This makes it an incredibly diverse and exciting area to work within!
In the last 10-15 years, microbiome research has yielded some fascinating insights. For example, it has been shown that different areas of the body (e.g. skin, mouth, gut) harbour a unique set of microbes. Each person shows variability between timepoints, but has a recognisably unique microbiome when compared to the profiles of other people. Interestingly, individuals who are related or cohabiting possess a more similar microbiome to each other than to strangers, revealing that a genetic and/or a local environmental component may exist.
Several factors have been shown to significantly affect the makeup of our microbial communities. Some of these are revealed in the fascinating TED talk given by microbiome pioneer Rob Knight (which really enthused me when I first came across this area of research!). Our microbiome develops from birth, meaning that a person’s immediate environment – including method of delivery – can significantly impact upon their microbiome and future health outcomes, for example, C-section babies have an altered early microbiome compared with those delivered naturally.
The gut microbiome has been studied in greatest depth, owing to it harbouring the largest bacterial community in the body. Once it ‘matures’ from around the age of 2 and a half years, other factors can continue to alter the microbiome across life, including medications (particularly antibiotics), diet and disease.
Despite these important observations, it is important to remember that there is still so much we are yet to know about the microbiome. The gut, for example, harbours a vast array of species, which together carry out a range of processes including manufacture of useful metabolites, yet isolating the effects of particular species and strains can be problematic. It can be difficult to ascertain accurate information at the species level as samples may not be sequenced at sufficient depth, particularly if the research goal is to observe associations with phenotypes of interest (e.g. obesity) at the genus or phylum taxonomic level. Furthermore, all these gut species coexist, meaning they may work together or compete for resources. Bacteria also have a symbiotic relationship with their hosts, meaning they will cooperate with us for mutually beneficial purposes. This means our genetics are likely to modulate bacterial function, suggesting the same bacterial species may act differently in different people. This may help to explain why certain people develop particular conditions or diseases, while others don’t: with dysbiosis (a disordered microbiome) implicated in disorders from obesity to depression. Indeed, the existence of the gut-brain axis adds further complexity, particularly for understanding psychological conditions or physiological diseases believed to also contain a psychological component, such as chronic pain syndromes or irritable bowel syndrome.
Therefore, it is important not to jump to conclusions regarding the role of the microbiome, or assume it can immediately be utilised as a treatment target for disease. There have been some therapies that have already been successfully utilised, such as fecal transplants for individuals with C. difficile infection and certain probiotics which have been found to be beneficial for some with gastrointestinal problems. However, stating that a certain food or probiotic will alleviate or ‘cure’ health problems is misleading at best, or even dangerous if patients subsequently neglect other treatments or medications which may have greater efficacy, particularly in the case of serious conditions. Despite this, probiotic, food and even medical and scientific companies have been guilty of jumping on the ‘microbiome bandwagon’, touting the benefits of probiotics or fermented foods, or recommending we do X or Y ‘for our microbiome’. It is too early in the microbiome journey to make specific claims or personalised recommendations, so we should treat those that we hear with caution. But, as research progresses this will hopefully become possible as we discover more about the currently hidden complexity of our bacterial symbionts.
If you would like to read more about the microbiome and the impact it has on our health check out the newly published issue of The Biochemist magazine.