A team of researchers from the Vall d'Hebron Institute of Research (VHIR), headed by Dr. Francisco Guarner, are the only Spanish participants in two studies that extend the MetaHIT Project. Both studies, published this Sunday July 6 in the Nature Biotechnology journal, represent one more step towards the knowledge of the intestinal microbiome. The first article provides an "http://www.nature.com/nbt/journal/vaop/ncurrent/full/nbt.2942.html" integrated catalog of gut microbial genes, which has increased from 3 to 10 million. Such a catalogue will allow scientists to determine the genetic and functional repertoire of a given gut microbiome and to understand how it is affected by geographical, temporal and physiological factors. Interestingly, the study reveals contry-specific gut-microbial signatures, as well as the presence of genes associated to antibiotic resistance.The second article explains how, thanks to a new approach in the "http://www.nature.com/nbt/journal/vaop/ncurrent/full/nbt.2939.html" analysis of complex metagenomic samples, more than 500 species have been identified in the human microbiome that were completely unknown until now.There is another landmark to add: not all the studied samples display such a high amount of unknown species. The intestinal flora of some individuals shows a smaller amount of unknown species and, in further analysis, it has been found to correspond to samples of patients diagnosed with Crohn's disease. "This brings up new data which we have to explore in detail", explains Dr. Francisco Guarner, "these species, unknown until now, will possibly make the difference between healthy and unhealthy people".These data are highly relevant because they open the door to new strategies aimed at recovering all these species through nutritional interventions: administering probiotics or fibers and other prebiotics that help the selective growth of some species. These unknown bacteria are most certainly the "good bacteria", as they are not the typical strains that produce an infection and this is the reason why they weren't isolated never before. "In these cases the stool transplant is not useful because they are most likely labile species, strictly anaerobic and dependent of the environment and,most certainly wouldn't survive outside the colon during the transplantation. The risk is that the transplant would favour the proliferation of non desirable species", continues Guarner.