The genus Romboutsia : genomic and functional characterization of novel bacteria dedicated to life in the intestinal tract

The genus Romboutsia: genomic and functional characterization of novel bacteria dedicated to life in the intestinal tract PhD thesis Jacoline Gerritsen, 2015 Abstract Humans, like other mammals, are not single-species organisms, but they constitute in fact very complex ecosystems. The extensive network of host-microbe and microbe-microbe interactions is tremendously important for our health, and we are just starting to unravel the mechanisms by which microbes contribute to host health and disease. Especially the intestinal tract of both humans and mammals contains an enormous diversity of microbial species of which many still remain to be cultured and characterized. There are numerous diseases for which aberrations in composition and diversity of the intestinal microbiota have been reported. Probiotic microorganism defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” have the potential to modulate the intestinal microbiota and thereby contribute to health and well-being. To this end, the relative abundance of a specific bacterial phylotype, named CRIB, was found to be associated with probiotic-induced changes in gut microbiota and decreased severity of pancreatitis and associated sepsis in an experimental rat model for acute pancreatitis studies. Later, a representative of this phylotype (strain CRIB) was isolated, and characterized using a polyphasic taxonomic approach. The taxonomy of several closely related members of the family Peptostreptococcaceae was revised in order to provide a valid systematic name to the isolate, for which Romboutsia ilealis was chosen. It was found that the majority of Romboutsia-associated 16S rRNA gene sequences have an intestinal origin, however, the specific roles that Romboutsia species play in the intestinal tract are largely unknown. To gain more insight in metabolic and functional capabilities of members of the genus Romboutsia, efforts towards the isolation of additional representatives were undertaken. This ultimately led to the isolation of a human small intestine-derived representative (strain FRIFI) of another novel Romboutsia species which was given the name R. hominis. Characterization of both novel species of intestinal origin, i.e. R. ilealis and R. hominis, belonging to the genus Romboutsia at the genomic and functional level provided first insights into the genetic diversity within the genus Romboutsia and their adaptation to a life in the (upper) intestinal tract. To this end, Romboutsia species are flexible anaerobes that are adapted to a nutrient-rich environment in which carbohydrates and exogenous sources of amino acids and vitamins are abundantly available. Microbiomic approaches such as those employed in this study can be used to pinpoint specific commensal microbes that might have a beneficial effect on the health of the host. In addition, the combination of genomic and functional analyses with single organisms and complex communities can be used to identify microbial functionalities that are related to health and disease, which in turn can be used to select potential probiotic strains based on specific functional properties. Ultimately, these approaches will lead to the characterization of (new) beneficial commensal microbes that exert health-promoting effects, with the ultimate possibility for them to be exploited as next-generation probiotics.