Journal: Applied and Environmental Microbioligy
Probiotic gut bacteria employ specific metabolic pathways to degrade dietary carbohydrates, beyond capabilities of their human host. Here we report how individual commercial probiotic strains degrade prebiotic (inulin type) fructans. First a structural analysis of the commercial fructose oligosaccharides/inulin samples used was performed.
These β(2-1) fructans differ in termination by either a glucose (GF) or a fructose residue (FF), with a broad variation in degree of polymerization (DP). Growth of individual probiotic bacteria on short-chain (sc)Inulin (Frutafit® CLR), a β(2-1) fructan (DP2-40), was studied. Lactobacillus salivarius W57 and other bacteria grew relatively poorly on scInulin with only fractions of DP3 and DP5 utilized, reflecting uptake via specific transport systems followed by intracellular metabolism.
Lactobacillus paracasei W20 completely used all scInulin components employing an extracellular exo-inulinase enzyme (glycoside hydrolase family GH32, LpGH32; also found in other strains of this species); the purified enzyme converted high DP compounds into fructose, sucrose, 1-kestose and F2 (inulobiose). Co-cultivation of L. salivarius W57 and L. paracasei W20 on scInulin resulted in cross-feeding of the former by the latter, supported by this extracellular exo-inulinase.
The extent of cross-feeding depended on the type of fructan, i.e. GF type (clearly stimulating) versus FF-type (relatively low stimulus), and on fructan chain-length, since relatively low DP β(2-1) fructans contain a relatively high content of GF-type molecules, thus resulting in higher concentrations of GF-type DP2-3 degradation products. The results provide an example of how in vivo cross-feeding on prebiotic β(2-1) fructans may occur amongst probiotic lactobacilli.