Fig. 6

Cellulosic isobutanol production using an optogenetically controlled eSSF process. a Schematic of the optogenetically controlled isobutanol and ethanol biosynthetic pathways, which compete for pyruvate from glycolysis. The enzymes which catalyse the first steps of each of these pathways are placed under optogenetic control (see “Methods”), with PDC1 of the ethanol pathway expressed in the light, and ILV2 of the isobutanol pathway expressed in the dark. The isobutanol pathway is localized to the mitochondria, whereas ethanol biosynthesis occurs in the cytosol. b Isobutanol titers recorded in eSSF and mcSSF experiments at 30 °C, using the optogenetic S. cerevisiae strain YEZ546-2 and different enzyme loads. All tests used either a 2% cellulose emulsion or 2% microcrystalline cellulose mixture and were switched from the light-driven growth phase to the darkness-induced production phase at the same cell density. Mean values are shown, and error bars represent the standard deviation of three independent replicates