Improved extracellular phytase activity in Saccharomyces cerevisiae by modifications in the PHO system.

Myo-inositol hexaphosphate (IP6, phytate) is a potent anti-nutritional compound occurring in many plant-based staple foods, limiting the bioavailability of important nutrients such as iron and zinc. The objective of the present study was to investigate different strategies to achieve high and constitutive extracellular IP6 degradation by Baker's yeast, Saccharomyces cerevisiae. By deleting either of the genes PHO80 and PHO85, encoding negative regulators of the transcription of the repressible acid phosphatases (rAPs), the IP6 degradation became constitutive, and the biomass specific IP6 degradation was increased manyfold.

Degradation of phytate by high-phytase Saccharomyces cerevisiae strains during simulated gastrointestinal digestion.

Hydrolysis of extracellular phytate (InsP(6)) by high-phytase yeast strains and survival of yeast cells were studied at simulated digestive conditions using yeast peptone dextrose growth medium and wheat gruel as model meals. An in vitro digestion method was modified to better correlate with the gastric pH gradient following food intake in vivo. High-phytase yeast gave a strong reduction of InsP(6) (up to 60%) in the early gastric phase, as compared to no degradation by wild-type strains.

Metabolism of extracellular inositol hexaphosphate (phytate) by Saccharomyces cerevisiae.

Iron and zinc deficiencies are global problems, frequently leading to severe illness in vulnerable human populations. Addition of phytases can improve the bioavailability of iron and zinc in food. Saccharomyces cerevisiae would be an ideal candidate as a bioavailability improving food additive if it demonstrates significant phytase activity.