Apparently identical bacteria can have a different effect

Our intestinal microbiome – the complement of the bacteria we carry in our intestines – has been badociated with many areas, from obesity to diabetes to heart disease and even neurological disorders and cancer. In recent years, researchers have sorted out the many bacterial species that populate the microbiome and asked which of them could be involved in specific disorders. But an article published today in Nature answered a new question: "What if the same microbe is different in different people?"

It has long been known that the genomes of microbes are not fixed, like ours. They are able to lose some of their genes, exchange genes with other micro-organisms or acquire new ones from their environment. Thus, a detailed comparison of the genomes of apparently identical bacteria will reveal DNA sequences present in one genome and not others, or possibly sequences that appear only once and several times in one genome. d & # 39; others. These differences are called structural variants. Structural variants – even the smallest ones – can result in huge differences in the interactions of microbes with their human hosts. A variant could be the difference between a mild presence and a pathogenic presence, or could confer bacteria resistance to antibiotics.

Drs. David Zeevi and Tal Korem, initially in the laboratory of Professor Eran Segal at the Weizmann Institute of Science, and then in their current positions at Rockefeller University and Columbia University, have developed algorithms to systematically identify structural variants at the within human intestinal microbiomes. The researchers began with microbiomes of nearly 900 Israeli subjects, in which they managed to identify more than 7,000 variants. They then collaborated with Dutch researchers from the University of Groningen (the Netherlands) and searched for these variants in the microbiomes of a large group of Dutch subjects. Most of the structural variants identified in Israeli subjects are also found among the Dutch, despite differences in genetics and lifestyle between groups.

The scientists then asked if any of the structural variants identified were badociated with health or disease. The group revealed more than 100 badociated with disease risk factors. Many of these badociations have been reproduced again in the Dutch cohort.

In one case, individuals whose microbiome had a certain variant in the genome of a particular microbial species were thinner by 6 kg and had a narrower waist circumference of 4 cm, on average, than those with same microbe – but not the one that hosts this particular variant. The scientists then badyzed the genes encoded on this variant and discovered that it confers on the bacterium the potential ability to transform certain sugars into a substance called butyrate. Butyrate is a small fatty acid that smells of rancid butter (hence its name, from ancient Greek to "butter"); Despite its odor, butyrate has anti-inflammatory effects and a positive influence on metabolism. This ability, the scientists explain, could help explain the difference in weight between carriers of bacteria with and those without the structural variant.

The results suggest that the method developed by the group could help researchers to identify the links between our microbiome, health and disease significantly, which could be omitted in other ways. "The real potential of this approach," says Zeevi, "is that it allows us to research the real mechanisms behind the badociations we find."

Segal believes that there could be tens of thousands of structural variants in the human intestinal microbiome, thousands of which could be badociated with a disease or risk of disease. As the composition of the microbiome has been implicated in many different syndromes and disorders, this research could have a lasting impact on the search for higher quality and more targeted probiotics for the treatment of the disease.