Project description:The Crabtree phenotype defines whether a yeast can perform simultaneous respiration and fermentation under aerobic conditions at high growth rates, a phenomenon that resembles the Warburg effect in cancer cells. Whole genome duplication, global promoter rewiring and loss of respiratory complex I are the main molecular events that contributed to the evolution of Crabtree effect. Here we show that overexpression of a single Gal4-like transcription factor is sufficient to convert Crabtree-negative Komagataella phaffii (Pichia pastoris) into a Crabtree positive yeast. We report the transcriptome profile (RNASeq) of the Δgal4-like and Gal4-like overexpression K. phaffii strains. Upregulation of the glycolytic genes and a significant increase in glucose uptake rate due to the overexpression of the Gal4-like transcription factor caused an overflow metabolism, triggering both short-term and long-term Crabtree phenotypes. This indicates that a single mutation leading to overexpression of one gene may have been sufficient as a first molecular event towards respiro-fermentative metabolism in the course of yeast evolution.
Project description:Prevention of COVID-19 on a global scale will require the continued development of high-volume, low-cost platforms for the manufacturing of vaccines to supply on-going demand. Vaccine candidates based on recombinant protein subunits remain important because they can be manufactured at low costs in existing large-scale production facilities that use microbial hosts like Komagataella phaffii (Pichia pastoris). Here, we report an improved and scalable manufacturing approach for the SARS-CoV-2 spike protein receptor binding domain (RBD); this protein is a key antigen for several reported vaccine candidates. We genetically engineered a manufacturing strain of K. phaffii to obviate the requirement for methanol-induction of the recombinant gene. Methanol-free production improved the secreted titer of the RBD protein by >5x by alleviating protein folding stress. Removal of methanol from the production process enabled scale up to a 1,200 L pre-existing production facility. This engineered strain is now used to produce an RBD-based vaccine antigen that is currently in clinical trials and could be used to produce other variants of RBD as needed for future vaccines.