Knock-out of the major regulator Flo8 in Komagataella phaffii results in unique host strain performance for methanol-free recombinant protein production.

Flo8 is a main transcriptional regulator of flocculation and pseudohyphal growth in yeast. Disruption of FLO8 in the popular recombinant protein production host Komagataella phaffii (Pichia pastoris) prevents pseudohyphal growth and reduces cell-to-surface adherence, making the mutant an interesting platform for research and industry. However, knowledge of the physiological impact of the mutation remained scarce. In-depth analysis of transcriptome data from FLO8-deficient K. phaffii revealed that Flo8 affects genes involved in cell cycle, mating, respiration, and catabolite repression additionally to flocculation targets. One gene with considerably increased expression in flo8 was GTH1, encoding a high-affinity glucose transporter in K. phaffii. Its promoter (P) was previously established as a strong, glucose-regulatable alternative to methanol-induced promoters. P and its improved derivatives P, D-P and D-P, proved to be promising candidates for controlling recombinant protein production in the FLO8-deficient background. In small-scale screenings, P-controlled intracellular EGFP levels were 2.8-fold higher, and yields of different secreted recombinant proteins were up to 4.8-fold increased. The enhanced productivity of the flo8 mutant in combination with the P variants was transferrable to glucose-limited fed-batch processes and could largely be attributed to higher transcriptional activity of the promoter, leading to a much higher productivity per chromosomally integrated gene copy. K. phaffii flo8 has many advantageous characteristics, such as reduced surface growth and increased transcriptional strength of glucose-regulatable promoters. These features turn the flo8 strain into a valuable new base strain for various experimental designs and establish flo8 as an excellent strain background for methanol-free recombinant protein production processes.