Carbon dioxide fixation in G. bemidjiensis. (a) The citrate lyase gene cluster and separately located gene Gbem_0190; some components are unique to G. bemidjiensis (pink arrows) and others have orthologs in G. sulfurreducens (green arrows). The catalytic subunits are encoded by citEF, the acyl carrier protein by citD, the cofactor synthesis enzyme by citG-1 and citG-2, the cofactor-transferring enzyme by citX, and the priming enzyme by citC. (b) The oxidative and reductive TCA cycles. Most enzymes that catalyze reductive reactions unique to G. bemidjiensis (pink arrows) also catalyze the oxidative reactions common to G. sulfurreducens and G. metallireducens (purple arrows). The exceptions are citrate lyase (reductive direction only) and citrate synthase and 2-oxoglutarate dehydrogenase (oxidative direction only).