Glycerol metabolism of Pichia pastoris (Komagataella spp.) characterised by 13C-based metabolic flux analysis

Metabolic flux analysis based on 13C-derived constraints has proved to be a powerful method for quantitative physiological characterisation of one of the most extensively used microbial cell factory platforms, Pichia pastoris (syn. Komagataella spp.). Nonetheless, the reduced number of carbon atoms and the symmetry of the glycerol molecule has hampered the comprehensive determination of metabolic fluxes when used as the labelled C-source. Moreover, metabolic models typically used for 13C-based flux balance analysis may be incomplete or misrepresent the actual metabolic network. To circumvent these limitations, we reduced the genome-scale metabolic model iMT1026-v3.0 into a core model and used it for the iterative fitting of metabolic fluxes to the measured mass isotope distribution of proteinogenic amino acids obtained after fractional 13C labelling of cells with [1,3-13C]-glycerol. This workflow allows reliable estimates to be obtained for in vivo fluxes in P. pastoris cells growing on glycerol as sole carbon source, as well as revising previous assumptions concerning its metabolic operation, such as alternative metabolic branches, calculation of energetic parameters and proposed specific cofactor utilisation.