Scientists find intestinal bacteria divided into enterotypes
An international team of scientists has discovered that the human's intestinal bacteria can be split into three main groups known as enterotypes. Presented in the journal Nature, the study highlights how intestinal bacteria in each enterotype arrange themselves into stable and distinct clusters with common features. These findings, which could lead to better information for people in need of medical or dietary help, are an outcome of the METAHIT ('Metagenomics of the human intestinal tract') project, which clinched EUR 11.4 million under the Health Theme of the EU's Seventh Framework Programme (FP7).
The research team METAHIT consists of academic and industry actors from Belgium, Brazil, China, Denmark, Finland, France, Germany, Italy, Japan, the Netherlands, Spain and the United Kingdom. According to them, various factors like health, age or place of residence have no impact on these types of intestinal bacteria.
The METAHIT scientists characterised the bacterial flora from the guts of 300 people from Europe, South America and Asia. Specifically, the studies had 39 people from Denmark, France, Italy, Japan, Spain and the United States; 85 people from Denmark; and 154 from the United States. After advanced bioinformatic analysis, their studies in these populations revealed three different groups of intestinal bacteria in people, named 'enterotypes' by the researchers. No differentiating factors such as age, gender, nationality or health played a critical role in the recognisable enterotypes.
Although much smaller than human cells, bacterial cells are very numerous in the human body: for each 1 of our own cells, there are 10 bacteria living in our bodies, most of them in the gut. Based on the research findings, the three enterotypes demonstrated different categories of bacteria with a different impact on the gut. That is, the Bacteroides intestinal bacteria dominate enterotype 1; the team also found that the bacteria form a distinctive cluster of gut flora along with other species of bacteria. Enterotype 2 is dominated by the Prevotella bacteria, and enterotype 3 is dominated by the main bacteria called Ruminococcus, in addition to other bacteria species like Staphylococcus and Gordonibacter. Enterotype 3 is the most common, the experts say.
The bacteria clusters also supply energy, according to the researchers. A case in point is enterotype 3, which specialises in breaking down mucin. A type of protein produced by the cells of the epithelium, mucin acts to produce and secrete gels into the body of the organism. Breaking down mucin, for instance, helps the gut absorb fragments as nutrition for the body. All three enterotypes produce vitamins. For example, enterotype 1 produces vitamin B7 (biotin), B2 (riboflavin) and C (ascorbic acid); and enterotype 2 produces vitamin B1 (thiamine) and folic acid.
Thanks to their bacteria clusters and variations in how they function, each enterotype reflects a distinctive way of producing energy that is very compatible with the person who hosts it. Bacterial populations may even work together with their hosts on different levels, thus affecting a person's health.
The METAHIT team has published the first catalogue of genes of human intestinal bacteria, what experts call the second genome, or the 'metagenome'. These populations of bacteria encode 150 times more genes than the human genome. In the catalogue, the researchers outline that from a range of more than 1 000 species of bacteria living in the human gut, each person is host to many hundred types of bacteria.
The findings of this study will help researchers and physicians in their quest to meet the needs of patients, particularly in terms of providing personal and preventive dietary and medical advice.