As one of the highest densities of microecology on earth, intestinal microbiota is a community of common future for human nutrition. The gut microbiota is closely related to human health and nutrition. Since birth, the human microbiome plays a crucial role in influencing the health of the host. Understanding the changes in the human gut microbiome helps to construct the intestinal microecosystem. Metagenomic sequencing analyses have been performed to explore the structure and function of human gut microbiota. This study used metagenomic sequencing to investigate the dynamic variation in mother and infant’s gut microbiota, the interaction between intestinal microbiota, and the function of intestinal microbiota.
The development of intestinal microbiota during the first 1,000 days of life will affect a person’s health throughout life (Agosti et al., 2017; Selma-Royo et al., 2019). Many factors determine the composition of intestinal microbiota in newborns. The method of delivery method plays an important role in the initial establishment of infant gut microbes (Yang et al., 2021). Arboleya and colleagues proposed that vaginal delivery and exclusive reliance on breastfeeding in early life are the gold standards for the establishment and development of healthy gut microbiota in infants (Arboleya et al., 2015). Bifidobacterium, Bacteroides, and Clostridium proliferate and become the dominant genera associated with early life (Thompson-Chagoyán et al., 2007). In the data we collected from our experiment, although Bifidobacterium was not found in the intestine of the newborn, Bacteroides was the dominant genus in the intestine. This was consistent with previous research. With the growth of the infant, the intestinal microbiota was more abundant, such as Ruminococcus gnavus, Klebsiella Pneumoniae, among others. Nevertheless, before six months, Bacteroides fragilis was still the highest relative abundance species in the infant’s intestine, which was beneficial to maintain the healthy environment of intestine and worthy of continuous attention and exploration. Our data also showed that the gut microbiota composition of the infant was much less complicated than that of the mother, which were in line with findings of previous studies.
Interestingly, we also observed differences in the richly differentiated taxonomic symbiotic network between the mother and infant. For example, in the infant’s intestine, Bacteroides fragilis, Methanobrevibacter smithii, etc were significantly positively correlated (P < 0.05), while Methanobrevibacter smithii generally appeared in the intestine of adults (Dridi et al., 2009). After obtaining this result, we repeated the investigation on the mother, and learned that the infant was fed by a mixture of breast milk and infant formula milk powder. In the study of Simpson M.R. et al., breastfeeding was one of the main factors affecting the early development of intestinal microbiota in infants (Simpson et al., 2018), which confirmed the important influence of breastfeeding on the development of intestinal microbiota in infants. For mixed infant, the composition of infant formula milk powder was very different from breast milk. For example, infant formula milk powder lacked key compounds found in human breast milk, such as HMOs (Kirmiz et al., 2018), which cause the intestinal microbiota of infants fed formula milk powder and breast milk very different (Schwarzenberg et al., 2018). Some studies have shown that formula milk powder might lead to the lack of Bifidobacteria in the intestinal microbial composition of infants (Hegar et al., 2019; Li et al., 2020), which was consistent with our findings.
The composition and activity of the intestinal microbiota co-develop with the host from birth, and are influenced by complex interactions with the host genome, nutrition, and lifestyle. Intestinal microbiota is involved in the regulation of multiple host metabolic pathways, mediating interactions between the host and bacterial metabolism, signal transduction, and immune and inflammatory nexus. These nexuses connect the gut, liver, muscle, and brain physiologically. An in-depth understanding of these nexuses is the prerequisite for optimizing therapeutic strategies to manipulate the gut microbiome to fight disease and improve health (Nicholson et al., 2012). Within these metabolic nexuses, multiple bacterial genomes could sequentially regulate metabolic responses, leading to combined metabolism of microbiome and host genomes to substrates (Nicholson & Wilson, 2003). The gut microbiota communicates metabolically with the host in a coordinated manner. After clustering analysis of metabolic pathways in the samples, we found that PWY-5676, GALACT-GLUCUROCAT-PWY, PRPP-PWY and others were consistent metabolic pathways in the infant and mother. Among of them, PWY-5676: acetyl-CoA fermentation to butanoate II pathway regulated the synthesis of butyric acid. Acetic acid, propionic acid, and butyric acid were the main short chain fatty acids (SCFAs) in the intestine. As the main energy source of intestinal cells, SCFAs regulate the absorption of a variety of nutrients in the intestinal tract, and are widely involved in energy metabolism, which are one kind of the most important products of intestinal microorganisms (Kasubuchi et al., 2015). This is also the evidence that the infant’s intestinal metabolic pathway is closer to adults. We speculated this might be due to the large differences in protein composition, lactose, fat, etc., between breast milk and infant formula milk powder. As a result, the structure and function of the microbiota in mixed diet fed infant were different from those in breastfed infants.
In conclusion, we found that the gut microbes were gradually established and perfected with the as the infant grew. Eutocia could promote the colonization of beneficial species in infant’s intestine, bringing the positive effects on the infant’s intestinal microflora. For the mixed diet feeding infant, the structure and function of intestinal microbiota were more similar to adults. Intestinal microbiota affects human development. Effectively using the information about intestinal microbiota could augment the human health. Better understanding about establishing mechanisms of intestinal microbiota in infants, and the prediction of infant’s intestinal microbiota, could provide a theoretical basis and guidance to promote the intestinal health of mothers and infants. However, this study was a scientific phenomenon discovered accidentally in experiment, further large-scale population experiments are needed.