*Geek Box: The ‘Bacterial Core’
In the course of our evolution, human beings have colonised every corner of the planet, adopting diverse diets in radically different natural environments and climates. Our gastrointestinal tract is one of the largest interfaces with our external environment [other than the skin], providing for both the digestion and absorption of essential nutrients and the first line of immune defence.
Within our GI system, particularly the colon, is a dynamic ecosystem of bacteria. At the broadest level, there are 4 main divisions, known as ‘phyla’: Firmicutes, Bacteroidetes, Actinobacteria and Proteobacteria. These phyla are considered our “bacterial core”, with the majority of bacterial types belonging to two major phyla, the Firmicutes and Bacteroidetes, and significant contributions from Actinobacteria and Proteobacteria.
Within each phylum, there are a multitude of different genus, and within the genus individual species. For example, the phylum Bacteroidetes contains the genus Prevotella, which contains different species, for example Prevotella copri [P.copri]. It is within the composition of each phyla – at the genus and species level – that significant inter-individual variability is observed. Diversity in the human gut thus reflects the depth and breadth of variability within each major phylum.
The exceptional diversity in our gut microbiota reflects diversity of environment, food sources, and consequent adaptations influencing host health.