Fig. 6: Taxon-specific distribution of enzymes involved in short-chain fatty acid (SCFA) biosynthesis.

KO functions detected in more than 6 datasets, with a mean abundance higher than 0.001% and mapping to KEGG pathways named carbon fixation pathways in prokaryotes (Wood-Ljungdahl pathway part), propanoate metabolism and butanoate metabolism are reported. Enzymes are listed based on the sequential order of the reactions within the pathways; each sub-pathway is preceded by a subtitle in italic. The color of each square corresponds to the mean percentage abundance between the 10 datasets (see color legend). Phyla are in bold, genera and species in italic, while higher taxa useful for classification but unassigned to any of the listed enzymes are into square brackets. The column “total” corresponds to the summed abundance of all taxon-specific assignments (including “Bacteria/unassigned”) for a given enzyme. THF, tetrahydrofolate. Enzymes from other butyrogenic pathways (glutarate pathway, lysine pathway, 4-aminobutyrate/succinate pathway) were detected in a small number of datasets and therefore the only acetyl-CoA pathway was selected for butyrogenesis. Acetyl-CoA C-acetyltransferase, although highly expressed in all the datasets, was not specifically included within butyrogenesis as it participates in many other diverse pathways. * Butyryl-CoA dehydrogenase (K00248) can also catalyze propionyl-CoA biosynthesis from acryloyl-CoA (last step of “lactate to propanoyl-CoA” part of propionogenesis).