Yasemin Saplakoglu writes:

A mother gives her baby her all: love, hugs, kisses … and a sturdy army of bacteria.

These simple cells, which journey from mother to baby at birth and in the months of intimate contact that follow, form the first seeds of the child’s microbiome—the evolving community of symbiotic microorganisms tied to the body’s healthy functioning. Researchers at the Broad Institute of the Massachusetts Institute of Technology and Harvard University recently conducted the first large-scale survey of how the microbiomes of a mother and her infant coevolve during the first year of life. Their new study, published in Cell in December found that these maternal contributions aren’t limited to complete cells. Small snippets of DNA called mobile genetic elements hop from the mother’s bacteria to the baby’s bacteria, even months after birth.

This manner of transfer, which has never been seen before in the cultivation of an infant’s microbiome, could play a crucial role in promoting growth and development. Understanding how a child’s microbiome evolves could explain why some children are predisposed to certain diseases more than others, said Victoria Carr, a principal bioinformatician at the Wellcome Sanger Institute who was not part of the study.

“It’s a big question: How do we get our microbes?” said Nicola Segata, a professor at the University of Trento in Italy who was also not part of the study.

Our bodies are home to about as many bacterial cells as human cells, and most of them live inside our guts. Each of us harbors massively diverse libraries of bacterial species and strains acquired throughout life. But babies start out almost sterile. The first major infusion of microbes is thought to come from the mother during birth as the infant exits the womb. That bacterial gift creates the scaffolding for a thriving microbial community in the body that sustains us for the rest of our lives. (Infants born by cesarean section don’t get the same initial infusion of microbes that babies get from vaginal birth, but they slowly gather them later.)

One of the microbiome’s effects, Segata explained, is to condition its host’s immune system and metabolism during the first couple of years of life. These initial training days “can have long-lasting consequences that are right now still difficult to comprehend,” he said. [Continue reading…]