Bioprocess optimization of glutathione production by Saccharomyces boulardii: biochemical characterization of glutathione peroxidase

• DOI: 10.1007/s00203-021-02584-0
• Publication Date: 2021-09-27T20:14:46Z
• Authors: Hossam Badr; Ashraf El-Baz; Ismail Mohamed; Yousseria Shetaia; Ashraf S. A. El-S...; Noha Sorour
• Keywords: Saccharomyces boulardii; 0106 biological sciences; 0301 basic medicine; Glutathione Peroxidase; 03 medical and health sciences; Saccharomyces cerevisiae; Glutathione; 01 natural sciences; Glutathione Synthase

Abstract The well-known probiotic GRAS Saccharomyces boulardii (CNCM I-745) was used for the first time to produce glutathione (GSH). The culture conditions affecting GSH biosynthesis were screened using a Plackett-Burman design (PBD). Analyzing the regression coefficients for 12 tested variables; 6 of them, including yeast extract, glucose, peptone and cysteine; temperature and agitation rate had a positive significant effect on GSH production with a maximum production of 192 mg/L. The impact of addition time of cysteine was investigated in 19 experiments during the growth time course (0-36 h), the best addition time was 8h post-inoculation producing 235 mg/L of GSH. The most significant variables were further explored at 5-levels using Central Composite Rotatable Design (CCRD), giving a maximum production of GSH (552 mg/L). Using baffled flasks, the GSH was increased to 730 mg/L, i.e 1.32-folds increment than obtained using CCRD. The two rate-limiting genes of GSH biosynthesis “γ-glutamyl cysteine synthetase (gsh1) and GSH-synthetase (gsh2) were amplified and sequenced to validate the GSH biosynthetic potency of S. boulardii. The sequences of genes showed 99% similarity with gsh1 and gsh2 genes of S. cerevisiae. Glutathione peroxidase was purified and characterized from S. boulardii with molecular mass and subunit structure of 80 kDa and 35 kDa as revealed from native and SDS-PAGE, ensuring its homodimeric identity. The activity of GPx was reduced by 2.5-folds upon demetallization confirming its metalloproteinic identity. The enzyme was strongly inhibited by hydroxylamine and DTNB, ensuring the implication of surface lysine and cysteine residues on the enzyme active site domains.