The bugs that colonise our gut (the microbiota) are in constant communication with the rest of our body. Eat a carb-heavy meal, or go out for a few too many drinks, it shifts in it composition. Have a course of antibiotics and you'll notice big differences in the bacteria in your gut. But it turns out that the nature, not nurture, might be the biggest driver of our gut microbiota.
In humans, the composition of the gut microbiota is reported to be more similar with closer degrees of relatedness in families. However, it has also been reported that monozygotic twins (identical) do not have more similar gut microbes comes to dizygotic twins (non-identical); although these results were from fairly small amounts of twins and therefore may not be powered to detect actual differences that exist.
Larger twin studies have shown that there are a certain subset of bacteria that are in fact hereditable, with the remaining species subject to change based on our environment, habits, medication, diseases and lifestyle.
But, how do we inherent bacteria? They are not human, and therefore cannot be passed down in our genes. And the answer is vertical transfer.
Much of this research has come from looking at the composition of the microbiome in infants and young children exposed to different early-life factors. Starting right at the beginning, babies born via caesarian section have a profoundly different bacterial composition compared to those born vaginally. They exhibit lower numbers of the good, or "commensal" bacteria (the ones you typically find in probiotics or Yakult), whilst having higher colonisation of nasty bacteria such as Clostridium Difficile (which can cause diarrhoea). And this all occurs because the baby is exposed to bacteria typically found on the skin and in hospitals instead of having direct contact with the mother's vaginal and intestinal flora.
It has also been shown that babies that are breast fed, have very different microbial compositions compared to those that are formula-fed, with breast-fed babies having higher levels of beneficial bacteria such as Bifidobacterium. This is thought to be due to breast milk containing a type of prebiotic that supplements the growth of these good bacteria.
These early differences tend to be sustained for a few months, but it is unclear if they continue into adolescence and adulthood, and their impact on disease development is still unclear.
Impact on disease..