Seasonal changes in the human microbiome
Research has revealed that our microbiome can fluctuate with the seasons.
The human microbiome is composed of all of the microbes found on or in the human body. These microbial cells outnumber human cells and include a vast number of bacteria, protists, fungi and viruses. They are found all over the body on the skin and inside in the body, for example in the lungs, but the microbial composition is most diverse and abundant in the gastrointestinal tract.
These microbes are beneficial to humans in a variety of ways. For example, they improve our ability to digest certain foods, provide certain vitamins and protect the body against some pathogens. The importance of the microbiome is highlighted when it is disrupted: microbiome disruption is associated with certain conditions such as inflammatory bowel diseases.
Recent research has revealed the first evidence of seasonal cycling in the gut microbiome composition. This research was carried out on a group of people known as the Hadza, in western Tanzania. The Hadza are do not have farm their own crops or livestock but instead are hunter gatherers. Their diet varies across the seasons, with more game such as warthogs in the dry season and more foraging in the wet season, meaning more berries and honey to eat.
The gut microbiota of the Hadza was found to be more diverse in the dry season than the wet season. In particular, bacteria of the Bacteroides genus were present in the dry season but disappeared in the wet season.
It was found that those microbes which varied most between seasons within the Hazda also differ hugely between more industrialised populations and traditional populations such as the Hadza.
The data collection itself involved retrieving a large number of swabs from stool samples from 188 Hadza people. The genetic information from the samples were then analysed in the lab.
Because of the similarity of the hunter gatherer lifestyle of the Hadza and our ancient human ancestors this research can give us some clues on the gut microbes of our ancient ancestors.
However, the window to conduct this research is sadly closing. The Hadza people are becoming more urbanised, with more people moving on to nearby villages each year, as well as the introduction of foods such as flour.