An estimated 20% of women of European descent are not able to produce mucous that have fucose sugars attached to the ends of their mucin molecules. These women are called ‘non-secretors’, as opposed to ‘secretors’ who can fucosylate their mucins. This rather peculiar genetic anomaly is not appreciated until it is looked at under the lens of the microbiome. Many of the microbiota in the gut feed off the host’s mucins for energy, and the lack of fucose is a major factor in dictating which communities can survive in their guts. During pregnancy the mother’s gut microbiota undergoes a dramatic shift, although what variables are important in determining this shift remain unknown. Last week though, researchers from Finland showed that secretor status was an important indicator in how a women’s gut microbiome shifts during pregnancy. They published their results in PLoS ONE.

The researchers sampled the gut microbiome of 71 women throughout their pregnancy, and compared it to the secretor status, as determined by genetic testing. In the first trimester of pregnancy each women, secretors and non-secretors alike, had similar diversities in their gut microbiota. However, by the third trimester the non-secretor’s gut microbiomes were much lower than their secretor counterparts. When the scientists measured specific phyla, they observed an increase in the abundance of Actinobacteria in the secreting women, and an increase In the abundance of Proteobacter in the non-secretors.

The changes in gut microbiota in these women may be very important to the microbiome of the infant that is born to them. As an infant passes through the birth canal he or she is exposed to the mothers’ vaginal and gut microbiota, and these bacteria serve as the initial populations that seed the infants’ own guts. In addition, some of these specific bacterial populations, such as Proteobacter, are implicated in diseases like IBD. If these bacteria persist in the mother after birth they may explain the onset or increased risk of some of these diseases.

We know that breastmilk is crucial to the development of a healthy infant’s microbiome. It contains many oligosaccharides that cannot be digested by the infant, and whose primary purpose appears to be stimulating the growth of specific microbiome bugs. There are, however, differences between new mothers’ milk. For instance, some mothers cannot produce 2′-fucosylated oligosaccharides, which are oligosaccharides that have a fucose sugar on the end. David Mills and his team at UC Davis recently investigated how the microbiomes of infants differed based on the presence or absence of fucosylated glycans in the milk that they drank. They published their work in the journal Microbiome last week.

Forty four infants who were fed breast milk had their microbiomes measured throughout the first 120 days of their lives. Thirty two of these infants were fed milk from woman with fucosylation ability (secretors), and twelve were from women without the fucosylation ability (non-secretors). When the researchers investigated the contents of the milk they found that it varied in many ways, besides fucosylation. For example, those women that did not fucosylate appeared instead to increase their monosaccharide sialylation, a sugar that has been linked to C. difficile infection. When the scientists compared the infants’ microbiomes in the two groups they discovered that secretor-fed infants achieved higher levels of Bifidobacteria and Bacteroides, and achieved these levels more quickly than non-secretor-fed infants. Instead, the non-secretor-fed infants had relatively higher levels of Enterobacteria, Clostridia, and Streptococci.

These differences may be important to the infants’ developments. For example, Bifidobacteria in the gut is associated with lower gut permeability and less inflammation. Also, Bifidobacteria and Bacteroides are large contributors to the production of short chain fatty acids and lactate, which have each been associated with gut health time and time again. A full 20% of the U.S. population is non-secretors, and it would be interesting to see if any epidemiologically significant differences exist between the two groups into adulthood. In either case, in the future it may be worth considering supplementing infant milk with fucosylated oligosaccharides if the lack of fucosylation does turn out to be detrimental to the baby.

The gut microbiome shift during pregnancy is related to the mother’s secretor status

Breastmilk varies between mothers – affects microbiome of infant