Effect of increasing oxygen partial pressure on Saccharomyces cerevisiae growth and antioxidant and enzyme productions.

This study investigated the impact of oxygen partial pressure on yeast growth. Saccharomyces cerevisiae cells were exposed to various hyperbaric air conditions from 1 bar to 9 bar absolute pressure (A). Batch cultures were grown under continuous airflow in a 750 mL (500 mL culture) bioreactor and monitored through growth rate and specific yields of ethanol and glycerol. In addition, the concentrations of antioxidant metabolites glutathione (reduced state, GSH and oxidized state, GSSG) and the activity of antioxidative enzymes superoxide dismutases (SOD) and catalases (CAT) were monitored. The results demonstrated that the different oxygen partial pressures significantly impacted the key growth parameters monitored. Compared with atmospheric pressure, under 2 to 5 bar (A), yeast cells showed higher growth rates (μ = 0.32 ± 0.01 h) and higher catalase (CAT) concentrations (214 ± 5 mU/g). GSH/GSSG ratio (6.36 ± 0.37) maintained until 6 bar (A) and total SOD (240 ± 5 mU/g) level significantly increased compared with 2 bar (A) until 7 bar (A). Under 6 to 9 bar (A), cell growth was inhibited, and a pressure of 9 bar (A) led to excessive GSSG accumulation (GSH/GSSG = 0.31 ± 0.06). The inhibition of t-SOD (160 ± 3 mU/g) and CAT (62.73 ± 0.2 mU/g) was observed under 9 bar (A). A reference experiment (8 bar (A) N + 1 bar (A) air) confirmed that the observed behaviors were entirely due to O. In addition to their utility in biotechnological process design, these results showed that growth impairment was solely due to oxidative stress induced by excessive oxygen pressure. KEY POINTS: • Yeast cells were grown in batch mode under 1 to 9 bar (A) air pressures and up to 5 bar (A) promoted then hindered growth. • The GSH/GSSG ratio was stable up to 5 bar (A) then GSSG accumulated to excess. • Complementary investigations of the activity of SOD and CAT validated growth limitations due to oxidative stress.