Figure 5. Altered balance of catabolic/anabolic carbon metabolism in Δhyd2 cells.

Cells lacking Hyd2 compensate for the loss of electrons derived from H₂ by increasing oxidation of organic carbon sources. There is an increased flux though the tricarboxylic acid cycle due to upregulation of enzymes involved in oxidative decarboxylation (e.g. ketoglutarate-ferredoxin oxidoreductase) (highlighted in yellow) and downregulation of those involved in anaplerosis (i.e. isocitrate lyase) (highlighted in blue). We model that loss of CO₂ through oxidative decarboxylation reactions is principally responsible for the decreased biomass of Δhyd2 cells. Oxidative pathways are depicted with green arrows, whereas reductive pathways are represented with blue arrows. The red text shows the expression ratios of the significantly upregulated or downregulated genes in Δhyd2 vs. wild-type cells.