A new synthetic medium for the optimization of docosahexaenoic acid production in Crypthecodinium cohnii

Abstract

The heterotrophic microalgae Crypthecodinium cohnii was usually cultivated in complex medium containing glucose, yeast extract and sea salt. For the preparation of DHA with highest purity, a new defined medium without the yeast extract was developed. Different inoculated densities, C/N ratios, temperatures, culture volumes and glucose additions were investigated to optimize the algal growth rate and DHA production. The growth period in C. cohnii was shortened from 12-14 days to 7-8 days, the OD600 was enhanced from 2.0 to 3.0, the glucose consumption was accelerated and used up on day 3-4, and the DHA content in culture were increased from 10 to 45 nmoles/300 μl batch. It was found that C. cohnii had optimal growth and DHA accumulation in 25 °C, 0.2 inoculated density, 5-10 C/N ratio, 5:1 air/culture volume ratio. This is the first time DHA production using C.cohnii has been optimized in synthetic medium. This allows preparation of uniformly radiolabeled 13C- and 14C-DHA.

Fig 1. Growth rate and DHA production in different inoculated densities.

A. OD₆₀₀; B, DHA content in culture, 1ml/batch.

Fig 2. Growth rate and DHA production in different glutamate concentrations.

A, OD₆₀₀; B, glucose consumption; C, DHA content in culture, 300 μl/batch.

Fig 3. Growth rate and DHA production in different temperatures.

A, OD₆₀₀; B, glucose consumption; C, DHA content in culture, 300 μl/batch.

Fig 4. Growth rate and DHA production at different air/culture ratios.

5 ml (9:1), 10 ml (4:1), 15 ml (2:1), and 20 ml (1.5:1) of medium in 50 ml tubes. A, OD₆₀₀; B, glucose consumption; C, DHA content in culture, 300 μl/batch.

Fig 5. Growth rates and DHA productions with adding additional glucose.

A, OD₆₀₀; B, glucose consumption; C, DHA content in culture, 300 μl/batch.