Creation of cell surface-engineered yeast that display different fluorescent proteins in response to the glucose concentration

We have successfully created a novel yeast strain able to monitor changes in environmental conditions by displaying either green fluorescent protein (GFP) from Aequorea victoria or blue fluorescent protein (BFP), a variant of GFP, on its cell surface as a visible reporter. For the display of these fluorescent proteins on the cell surface of Saccharomyces cerevisiase, our cell-surface-engineering system was utilized. The GAPDH promoter, which is active in the presence of glucose, and the UPR-ICL promoter from Candida tropicalis, which starts to function in the presence of a reduced level of glucose, were employed simultaneously to express the GFP-encoding gene and the BFP-encoding gene, respectively. This cell-surface-engineered yeast strain emitted green fluorescence from the cell surface when sufficient glucose was present in the medium, and blue fluorescence from the same cell surface when the glucose in the medium was consumed. The fluorescent proteins displayed on the cell surface using the different promoters enabled us to monitor the concentrations of intra- and/or extracellular glucose that regulated activation or inactivation of the promoters. This novel yeast strain could facilitate the computerized control of various bioprocesses measuring emitted fluorescence.