FIGURE 1.

Anerobic metabolic routes in C. reinhardtii. Under dark anoxia, starch is metabolized to pyruvate via glycolysis, thereby generating ATP and reducing power (NADH). The network shows a pyruvate branch point with four enzymes. Another branch point is acetyl-CoA that can be used to produce ethanol via ADHE or acetate via the PTA-ACK pathway. Network is simplified by the omission of the subcellular localization of the different enzymes. Fe and Zn indicate the metal in the active site of the alcohol dehydrogenases. To better understand the metabolic responses, the number of oxidizable electrons is indicated for each metabolite. The main fermentation route used by the alga incubated in AIB under dark anoxia is the “PFL-gated pathway,” which consists of PFL, ADHE, and PTA-ACK.