Rôle des glycosidases des bactéries orales dans la perception des saveurs chez l'homme

Glycosidases, particularly β-glucosidases, catalyze the hydrolysis of glycosidic bonds, releasing sugar molecules and aglycones. In the human oral cavity, β-glucosidases from the oral microbiota have previously been proposed to release aromatic compounds.This thesis aims to identify bacterial oral glycosidases involved in aroma release. Seven glycosidases from the oral microbiota were identified, expressed, and purified, including those from Veillonella sp. (VsBGlu1 and VsBGal1), Prevotella sp. (PsBG1), Streptococcus pneumoniae (SpBG1), Actinomyces naeslundii (AnBG1), Streptococcus salivarius (SsBG1), and Granulicatella adiacens (GaBG1). Kinetic analysis showed that PsBG1 has high catalytic efficiency towards β-glucopyranosides and can hydrolyze various aromatic and aliphatic glucosides, releasing volatile compounds such as salicylaldehyde, octanol, and hexanol. X-ray crystallography analysis of PsBG1 revealed its characteristic glycoside hydrolase family 1 structure. Through co-crystallization with a glycerol molecule, a set of amino acids was proposed for their roles in substrate recognition and catalysis. In a complex food matrix, PsBG1 effectively hydrolyzed glycosidic substrates into volatile metabolites. The β-glucosidases from Actinomyces naeslundii and Granulicatella adiacens also showed activity towards aromatic glycoside substrates found in food products.This study provides a detailed characterization of human oral microbiota β-glucosidases, demonstrating their role in the hydrolysis of aroma precursors and their potential role in flavor perception.