The number has been run off many times by now, but it remains impressive: The human gut contains, at a rough estimate of course, about 1014 types of microorganisms which happily intermix and interact with each other. In purely numerical terms, that’s ten times as many microorganisms as there are body cells. Looked at from this perspective, man is thus a tube-like bacterial culture with an attached body which mostly serves to provide the bacterial mass – two kilograms per person – with sufficient nourishment.
Discovered: The blood group of the intestine
Not much is really known yet about our intestinal coinhabitants. They are involved in energy metabolism in the human body by converting polysaccharides into short chain fatty acids. They manufacture some vitamins and have a variety of immunological functions. It is also known that the intestinal flora of patients with Crohn’s disease significantly differ from those in healthy people. Scientists led by Peer Bork at the European Molecular Biology Laboratory (EMBL) in Heidelberg have tried to bring some more light into the darkness of this area of knowledge and in April even made it with their research into the journal Nature. “We have discovered that the arrangement of microbes in the human intestine is not random,” says Bork. “Our gut flora can be divided into three different types – one might also speak of three different ecosystems.”
The analyses were based on stool samples from nearly 280 volunteers from Europe, America and Asia. The various enterotypes differ essentially in the type and proportion of the particular groups of bacteria. This, in turn, leads to differences in vitamin synthesis or in haem synthesis. Why there are different enterotypes is unclear. It seems however that these enterotypes are relatively constant. If this proves true, they would have a certain resemblance to blood groups, which also don’t change over one’s lifetime. Perhaps the respective enterotype is immunologically determined, says Bork. Some immune systems seem to tolerate one bacteria, some tolerate another one better.
Eating according to intestinal state
So far, so good. The question now is, of course, which conclusions individuals should draw from these findings. Mani Arumugam, lead author of the study, recently philosophised about it at an event at the EMBL. It’s conceivable, for example, that the different enterotypes have an impact on how drugs are metabolised, says Arumugam. Put another way: perhaps the concept of personalised drug therapy will not only, as until now, centre on human genotype or genotype of tumor, but also on the composition of bacterial flora colonies.
What is right medically, is right with diet. If intestinal bacteria are involved in energy metabolism, it would have some say in deciding whether a person is prone to obesity or not. Perhaps enterotype-adjusted diets could be prescribed which are perfectly tailored to the individual metabolic setup in the intestine.
Facebook for digestion fetishists
Of course at this point this is all pure speculation. What is needed are data sets that correlate the individual enterotype with real-life data. In order to move forward on this, the EMBL scientists have now given a starting push to an until-now unique project with the name my.microbes. It is by nature a combination of genome project and social network. The participants – 5000 are initially being sought from around the world, each needing to contribute at least € 1451 to the cost – send one or multiple stool samples to the reference laboratory at specific intervals. There, the DNA of the intestinal flora is extracted and sequenced.
In addition, participants fill out a questionnaire, which includes a set of personal data. This data is anonymous and will not allow identification of the person. Among the questions that scientists hope to clarify in the first place is the influence of diet and gastrointestinal diseases on the intestinal flora. Geographical and ethnic differences are to be evaluated, in addition to possible changes in the individual enterotype over time and dependent on changing life situations.
As a small reward for their double-donation to science, participants can have personal and functional maps of their gut flora produced, which not only look quite colorful, but can – thanks to data coming from the participant’s allies in the cause – be placed in a global context. There will also be an Internet platform created that allows contact with fellow participants who have a similar enterotype. Why this should be interesting is not entirely clear. Perhaps, however, interesting starting points for a direct exchange of communication will indeed emerge from the bimonthly-updated analyses.