This is a placeholder for the introductory discussion on functional ecology of the HGM.

HMOSs are Prebiotics That
Stimulate Colonization by
Mutualist Bacteria
Beneficial bacteria of the gut microbiota,
such as bifidobacteria and lactobacilli, are
used as probiotics when they are deliberately
added to the diet with the intent of
increasing the relative amounts of these
beneficent bacteria in the microbiota. The
other approach to increasing their numbers
in the gut is to feed indigestible dietary
glycans, prebiotics, which when
consumed orally, arrive intact in the distal
intestine. These glycans then can selectively
support growth of beneficial microbiota,
including those used as common
probiotics that benefit host health by
improving fecal quality, reducing risks
of gastrointestinal infections, and decreasing
the incidence of allergic symptoms.
The mucosal surface contains
no enzyme that can digest HMOSs.
Therefore, HMOSs pass through the
small intestine and arrive at the heavily
colonized distal intestine, where key predominant
species of the microbiota metabolized
HMOSs. Bifidobacterium is a
genus with high concentration in
breastfed infant gut. The ability of Bifidobacterium
to metabolize HMOS is
attributed to clustered genes within
conserved loci that allow oligosaccharide
processing and transport. In 25 major
isolates of the human intestinal microbiota,
HMOSs most strongly stimulate
growth of Bifidobacterium spp. and Bacteroides
spp.26 (26. Yu ZT, Chen C, Kling DE, et al. The principal
fucosylated oligosaccharides of human milk exhibit
prebiotic properties on cultured infant microbiota.
Glycobiology. 2013;23:169–177.)

Isolated human gut microbes
selectively use major fucosylated
and sialylated HMOSs,27 (27. Yu ZT, Chen C, Newburg DS. Utilization of
major fucosylated and sialylated human milk
oligosaccharides by isolated human gut microbes.
Glycobiology. 2013;23:1281–1292.)

and, conversely,
the principal fucosylated oligosaccharides
of human milk exhibit prebiotic properties
on cultured infant microbiota. Feeding
20-FL and 3-fucosyllactose (3-FL) to
mice increased levels of bacteria of the
Porphyromonadaceae family, especially
members of the genus Barnesiella, in the
lumen of the gut.28 (Weiss GA, Chassard C, Hennet T. Selective proliferation
of intestinal Barnesiella under fucosyllactose
supplementation in mice. Br J Nutr.
2014;111:1602–1610.)

A synthetic mixture of
galactosyloligosaccharides is a commonly
used prebiotic to stimulate growth of
bifidobacteria in the gastrointestinal
tract. The earliest human milk, colostrum,
contains galactosyllactoses, which are also
principal components of synthetic
galactosyloligosaccharide, and the colostrum
galactosyllactoses likely exhibit the
same prebiotic effect, suggesting additional
critical roles in modulating initiation
of a healthy microbiota by human
colostrum.19  (He Y, Newburg DS. Glycobiology of human milk
in health and disease. In: Wiederschain GYa, ed.
Glycobiology and Human Disease. CRC Press;
2015. (In press).)

Newburg2015