Fig. 1. The Custers effect of B/D bruxellensis. (A) Schematic overview of main factors influencing the redox balance and growth pattern. The redox balance is the main responsible for the Custers effect observed in B/D bruxellensis, which can ferment glucose to ethanol more rapidly in aerobic than anaerobic conditions. The conversion of glucose-3-phosphate (G3P) to glycerol is typically limited or even absent in B/D bruxellensis, due to limited (or absent) glycerol 3-phosphate phosphatase activity (indicated with an X). Nitrate assimilation abolishes the Custers effect by allowing the cell to replenish the NAD(P)H pool through reduction of nitrate to ammonium (cf. Section 3.2.1.2.2).
B) Effect of a shift from aerobic to anaerobic culture conditions on the growth kinetics of B/D bruxellensis. The lag phase at the transition from an aerobic to anaerobic environment is caused by the blockage of glycolysis due to a lack of NAD+. Only when other (slow) routes of intracellular NADH re-oxidation are activated, B/D bruxellensis will be able to escape this lag phase and will start producing ethanol again (without producing acetic acid). See text for more details.