INFLUENCE OF OXYGEN AND GLUCOSE ON PRIMARY METABOLISM AND ASTAXANTHINPRODUCTION BY PHAFFIA-RHODOZYMA IN BATCH AND FED-BATCH CULTURES - KINETIC AND STOICHIOMETRIC ANALYSIS

The influence of the oxygen and glucose supply on primary metabolism ( fermentation, respiration, and anabolism) and astaxanthin production i re the yeast Phaffia rhodozyma was investigated; When P. rhodozyma gre w under fermentative conditions with limited oxygen or high concentrat ions of glucose, the astaxanthin production rate decreased remarkably. On the other hand, when the yeast grew under aerobic conditions, the astaxanthin production rate increased with increasing oxygen uptake. A kinetic analysis showed that the respiration rate correlated positive ly with the astaxanthin production rate, whereas there was a negative correlation with the ethanol production rate. The influence of glucose concentration at a fixed nitrogen concentration with a high level of oxygen was then investigated. The results showed that astaxanthin prod uction was enhanced by an initial high carbon/nitrogen ratio (C/N rati o) present in the medium, but cell growth was inhibited by a high gluc ose concentration. A stoichiometric analysis suggested that astaxanthi n production was enhanced by decreasing the amount of NADPH required f or anabolism, which could be achieved by the repression of protein bio synthesis with a high CIN ratio. Based on these results, we performed a two-stage fed-batch culture, in which cell growth was enhanced by a low CIN ratio in the first stage and astaxanthin production was enhanc ed by a high CIN ratio in the second stage, In this culture system, th e highest astaxanthin production, 16.0 mg per liter, was obtained.