Summer Meeting 2013: growth and physiology of bifidobacteria

Bifidobacteria are a minor fraction of the human colon microbiota with
interesting properties for carbohydrate degradation. Monosaccharides such as
glucose and fructose are degraded through the bifid shunt, a dedicated
pathway involving phosphoketolase activity. Its stoechiometry learns that three
moles of acetate and two moles of lactate are produced per two moles of
glucose or fructose that are degraded. However, deviations from this 3 : 2 ratio
occur, depending on the rate of substrate consumption. Slower growth rates
favour the production of acetate and pyruvate catabolites (such as formate) at
the cost of lactate. Interestingly, bifidobacteria are capable to degrade inulintype
fructans (ITF) (oligofructose and inulin) and arabinoxylanoligosaccharides
(AXOS). Beta-fructofuranosidase activity enables bifidobacteria
to degrade ITF. However, this property is strain-dependent. Some strains
consume both fructose and oligofructose, with different preferences and
degradation rates. Small oligosaccharides (degree of polymerization or DP of
2-7) are taken up, in a sequential order, indicating intracellular degradation
and as such giving these bacteria a competitive advantage towards other
inulin-type fructan degraders such as lactobacilli, bacteroides and roseburias.
Other strains consume long fractions of oligofructose and inulin. Exceptionally,
oligosaccharides with a DP of up to 20 (long-chain inulin) are consumed by
specific strains. Also, the degradation of AXOS by a-arabinofuranosidase and
b-xylosidase is strain-dependent. Particular strains consume the arabinose
substituents, whether or not together with a consumption of the xylose
backbones of AXOS, either up to xylotetraose or higher and either extra- or
intracellularly. The production of high amounts of acetate that accompanies
inulin-type fructan degradation by bifidobacteria cross-feeds other colon
bacteria involved in the production of butyrate. However, bifidobacterial
strain-dependent differences in prebiotic degradation indicate the existence of
niche-specific adaptations and hence mechanisms to avoid competition among
each other and to favour coexistence with other colon bacteria.

Jaar van publicatie:2013

Trefwoorden:arabinoxylan-oligosaccharides, bifidobacteria, cross-feeding, inulin-type fructans