3.3 Geographical location and microbiome diversity

Interestingly, the ratio of these two groups has been found to consistently change depending on the geographical latitude of the human hosts.

The further North humans live, the more Firmicutes they have in their microbiome, whereas humans living nearer to the Equator have more Bacteroidetes (Suzuki and Worobey, 2014). As you will learn in Section 4, the ratio of Firmicutes to Bacteroidetes is important in several health conditions, such as Crohn’s disease and obesity. So, this difference in the diversity of microbiota within the microbiome may in part explain the geographical difference in some health conditions. However, it is still unclear why there is this difference, but possible contributing factors include:

• ethnicity
• diet
• Bergmann’s rule (populations at higher latitudes have on average a higher body mass to withstand colder conditions)
• climate
• other microorganism distribution, especially pathogens/parasites.

While the reasons for the geographical variations in the diversity of the gut microbiome are still not clear, and much research is underway, geographical effects do appear to play an important role in the diversity of the microbiome. However, an important consideration is that human geography is complex, and may be linked to factors such as socioeconomic status. Additionally, differing diet in different geographical regions may have a significant impact and you are going to learn more about this next.