The differing prevalences of propionate and butyrate producing bacteria in the human gut microbiota

Propionate and butyrate are major fermentation products released during the anaerobic growth of bacteria in the large intestine with strong implications on host health. While the different metabolic pathways leading to the release of these products are biochemically well characterized, less is known about their relative abundances across hosts and conditions. Here, we introduce a bioinformatics pipeline which connects pathway analyses, gene identification via sequence homology, and the screening of metagenomic samples to systematically identify the abundances of propionate producing pathways across individuals and in relation to butyrate producing pathways. We found that on average 36% of all genomes of a gut microbiota carried propionate producing pathways with the sodium-pumping succinate pathway being the most prevalent. This pathway abundance was anti-correlated to the abundance of butyrate pathways and greatly depended on host physiology. For example, propionate pathway abundance varied strongly among infants with a substantially higher abundance in vaginally than C-section born infants, increased in early adulthood, and decreased again with higher ages. This is in strong contrast to the known variation of butyrate pathway abundance, which is close to zero in infants and steadily increases with age. These results highlight the contrasting prevalence of both fermentation products at the individual level with shifts in microbiota composition resulting in strong consequences on the amount of butyrate and propionate available to the host.