Consumption of fermentable dietary fibers (DFs), which can induce growth and/or activity of specific beneficial populations, is suggested a promising strategy to modulate the gut microbiota and restore health in microbiota-linked diseases. Until today, inulin and fructo-oligosaccharides (FOS) are the best studied DFs, while little is known about the gut microbiota-modulating effects of β-glucan, α-galactooligosaccharide (α-GOS) and xylo-oligosaccharide (XOS). Here, we used three continuous in vitro fermentation PolyFermS model to study the modulating effect of these DFs on two distinct human adult proximal colon microbiota, independently from the host. Supplementation of DFs, equivalent to a 9 g daily intake, induced a consistent metabolic response depending on the donor microbiota. Irrespective to the DF supplemented, the Bacteroidaceae-Ruminococcaceae dominated microbiota produced more butyrate (up to 96%), while the Prevotellaceae-Ruminococcaceae dominated microbiota produced more propionate (up to 40%). Changes in abundance of specific bacterial taxa upon DF supplementation explained the observed changes in short-chain fatty acid profiles. Our data suggest that the metabolic profile of SCFA profile may be the most suitable and robust read-out to characterize microbiota-modulating effects of a DF and highlights importance to understand the inter-individual response to a prebiotic treatment for mechanistic understanding and human application.

In Italy, fermented sausages (called "salami") are consumed in large quantities. Salami samples from a local meat factory in the area of Torino were analysed at 0, 3, 7, 30 and 45 days of ripening. Swab samples from the production environment were collected as well at the beginning of the experiment. The diversity of metabolically active microbiota occurring during the natural fermentation of salami was evaluated by using RT-PCR-DGGE coupled with RNA-based pyrosequencing of the 16S rRNA gene. A culture-dependent approach was also applied to identify and characterize isolated Staphylococcaceae and LAB populations.Staphylococcus succinus, S. xylosus and Lactobacillus sakei were the species more frequently isolated during the maturation time. Rep-PCR analysis showed that S. succinus and S. xylosus isolated from swabs and salami samples clustered together suggesting a possible contamination during the production process. RT-PCR-DGGE and rRNA based pyrosequencing showed that the metabolically active populations were dominated by S. succinus, Lb. sakei and Leuconostoc carnosum. In this specific case study, only few species belonging to Staphylococcaceae, Lactobacillaceae and Leuconostocaceae may be metabolically active and contribute to determine the final characteristics of the products.

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