FIG 7.

Pathway of acetate metabolism in G. sulfurreducens during growth on NBAF medium with fumarate as the electron acceptor and acetate as the electron donor. Acetate is transported into the cells (green arrow) via acetate permease (magenta protein channel). Imported acetate can be activated via one of the following two pathways: (i) the acetate kinase (EC 2.7.2.1) followed by the activity of phosphotransacetylase enzyme (EC 2.3.1.8) (purple arrows) producing acetyl-CoA which is directed toward pyruvate synthesis and subsequently into biomass and amino acid synthesis pathways, or (ii) acetate being oxidized through conversion of succinyl-CoA to succinate via the activity of succinyl-CoA:acetate CoA-transferase enzyme (EC 2.8.3.18), resulting in the production of acetyl-CoA (yellow arrows) which is directed toward the TCA cycle. The fumarate provided in the medium is taken up (green arrow) via the fumarate transporter proteins (C₄-dicarboxylic acid transporter). Imported fumarate can either be (i) directed toward the TCA cycle (blue arrow), which operates as an open loop and ends with the formation of succinate and its excretion into the medium (red arrow), or (ii) reduced to succinate via the activity of inner membrane-bound FrdCAB enzyme (fumarate reductase activity) followed by its excretion into the medium (red arrow) (66, 67, 76, 77).