Multifactorial interaction and influence of culture conditions on yellow fluorescent protein production in Phaeodactylum tricornutum

Phaeodactylum tricornutum is a promising host for light-driven synthesis of heterologous proteins. However, the marine cold-water environment and alkaline-acidic pH shifts in the culture, necessitated by the diatom's growth requirements. In this study, we analyzed the influence of growth condition on maturation and dynamics of the yellow fluorescent protein (YFP) in episomal-transformant P. tricornutum. A mathematical model was developed to detect the parameters that affect biomass and YFP production. Optimized conditions increased YFP mean fluorescence intensity (MFI) per cell by 4.2-fold (3.6 ± 0.6 to 15.4 ± 1.1) and total protein levels in the culture by 1.8-fold (123 ± 4 to 219 ± 9 µg L^-1), without affecting biomass. YFP stability studies in P. tricornutum showed that the ubiquitin-proteasome system contributes the degradation of the recombinant protein, whereas newly synthesized YFP remains stable for up to 12 h. This optimization provides insights into the fluorescent protein-based heterologous production in diatoms.