Figure 1.

Overview of the fermentation metabolism in Clostridioides difficile. (A) Schematic overview of Stickland reactions showing the reaction steps of classical reductive and oxidative pathways and of the Rnf complex and the connection to the electron bifurcating enzymes. Products are shown at the end of the arrow and in boxes alongside the arrows, * Serine, threonine, methionine and cysteine are also subject to deamination by lyases. (B) Overview of amino acids and glucose as representative sugar and their fermentation products. The figure summarizes published fermentation products and substrates omitting alcohols and intermediates of the pathways for reasons of clarity. Corresponding alcohols are only minor products. (-OH: -hydroxy, Fd_ox: Ferredoxin oxidized form, Fd_red: Ferredoxin reduced form). Green: oxidative Stickland reactions and their products, gray: reductive Stickland reactions and their products, orange: central carbon metabolism-associated fermentation products, black: Stickland products (oxidative and/or reductive) and central carbon metabolism-associated fermentation products.