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

Abstract

This study investigated the impact of oxygen partial pressure on yeast growth. Saccharomyces cerevisiae cells were exposed to various hyperbaric air conditions from 1bar to 9bar absolute pressure (A). Batch cultures were grown under continuous airflow in a 750mL (500mL 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 5bar (A), yeast cells showed higher growth rates (μ = 0.32 ± 0.01h-1) and higher catalase (CAT) concentrations (214 ± 5mU/g). GSH/GSSG ratio(6.36 ± 0.37) maintained until 6 bar (A) and total SOD (240 ± 5mU/g) level significantly increased compared with 2bar (A) until 7bar (A). Under 6 to 9bar (A), cell growth was inhibited, and a pressure of 9bar (A) led to excessive GSSG accumulation (GSH/GSSG = 0.31 ± 0.06). The inhibition of t-SOD (160 ± 3mU/g) and CAT (62.73 ± 0.2mU/g) was observed under 9bar (A). A reference experiment (8bar (A) N2 + 1bar (A) air) confirmed that the observed behaviors were entirely due to O2. 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 9bar (A) air pressures and up to 5bar (A) promoted then hindered growth. • The GSH/GSSG ratio was stable up to 5bar (A) then GSSG accumulated to excess. • Complementary investigations of the activity of SOD and CAT validated growth limitations due to oxidative stress.