Production of Carotenoid-/Ergosterol-Supplemented Biomass by Red Yeast Rhodotorula glutinis Grown Under External Stress

The aim of this study is to compare the production of biomass enriched with carotenoids and ergosterol by yeast strain Rhodotorula glutinis CCY 20-2-26 grown under optimal growth conditions and in the presence of exogenous stress factors. R. glutinis cells were exposed to UV irradiation, oxidative stress (2–10 mmol/L H2O2) and osmotic stress (2–10 % NaCl). During the experiment, growth characteristics and the production of biomass, carotenoids and ergosterol were evaluated. Experiments were carried out in Erlenmeyer flasks and in laboratory fermentor. First, R. glutinis cells were exposed to higher concentration of stress factors added into the production medium. Further, low concentrations of NaCl and H2O2 were added to the inoculum medium or to both inoculum and production media. Exposure of red yeast cells to all tested stress factors resulted in higher production of carotenoids as well as ergosterol, while biomass production was changed only slightly. Under high stress, 2–3 times increase of b-carotene was observed. The addition of low salt or peroxide concentration into the inoculation media led to about 2-fold increase of carotenoid production. In Erlenmeyer flasks the best effect on the carotenoid and ergosterol production (3to 4-fold increase) was exhibited by the combined stress: the addition of low amount of NaCl (2 %) into the inoculum medium, followed by the addition of H2O2 (5 mmol/L) into the production medium. The production of ergosterol in most cases increased simultaneously with the production of carotenoids. Cultivation of R. glutinis carried out in a 2-litre laboratory fermentor was as follows: under optimal conditions about 37 g/L of yeast biomass were obtained containing approx. 26.30 mg/L of total carotenoids and 7.8 mg/L of ergosterol. After preincubation with a mild stress factor, the yield of biomass as well as the production of carotenoids and ergosterol substantially increased. The best production of enriched biomass was obtained in the presence of peroxide in the inoculation medium (52.7 g/L of biomass enriched with 34 mg/L of carotenoids) and also under combined salt/peroxide or salt/salt stress (about 30–50 g/L of biomass enriched with 15–54 mg/L of total carotenoids and about 13–70 mg/L of ergosterol). R. glutinis CCY 20-2-26 could be used as a potential biotechnological producer of carotenoid-rich biomass.