Effects of different glycerol feeding strategies on S-adenosyl-l-methionine biosynthesis by PGAP-driven Pichia pastoris overexpressing methionine adenosyltransferase

Methionine adenosyltransferase (MAT) was overexpressed within Pichia pastoris employing the promoter of glyceraldehyde-3-phosphate dehydrogenase gene (PGAP), to biosynthesize S-adenosyl-l-methionine (SAM). Effects of five glycerol feeding tactics on MAT activity were first investigated. Strategies A–C were based on limited feeding correlated with dissolved oxygen (DO) at 50.0%, 25.0% and 0.0%, respectively. For strategies D and E, unlimited supplementation was executed by pulsed feeding mode. Gradual decline (2–0%) (w:v) of the residual glycerol level was shown between any two pulses in strategy D, while a nearly stable content (2%) throughout fed-batch cultivation with strategy E. With shifting strategies A–E in alphabetical order, gradual improvements of MAT activities were achieved, with the maximum of 9.05 U g−1 dried biomass for strategy E, since the specific glycerol consumption rate (FG) ascended due to the elevated specific oxygen uptake rate (qO2qO2). The success was ascribed to the enhancement of oxygen transfer rate (OTR), because 2% glycerol improved oxygen saturation content in broth (C*) and volumetric oxygen transfer coefficient (kLa).Strategy E also led to the highest values of ATP and biomass besides MAT. Consequently, the highest SAM yield and volumetric level were obtained at 0.058 g g−1 and 9.26 g l−1, respectively.