Heterotrophic production of biomass and lutein by Chlorella protothecoides on various nitrogen sources

The effects of nitrate, ammonium, and urea as nitrogen sources on the heterotrophic growth of Chlorella protothecoides were investigated using flask cultures. No appreciable inhibitory effect on the algal growth was observed over a nitrogen concentration range of 0.85–1.7 g l−1. In contrast, differences in specific growth rate and biomass production were found among the cultures with the various nitrogen compounds. The influence of different nitrogen sources at a concentration equivalent to 1.7 g l−1 nitrogen on the heterotrophic production of biomass and lutein by C. protothecoides was investigated using the culture medium containing 40 g l−1 glucose as the sole carbon and energy source in fermentors. The maximum biomass concentrations in the three cultures with nitrate, ammonium, and urea were 18.4, 18.9, and 19.6 g l−1 dry cells, respectively. The maximum lutein yields in these cultures were between 68.42 and 83.81 mg l−1. The highest yields of both biomass and lutein were achieved in the culture with urea. It was therefore concluded that urea was the best nitrogen source for the production of biomass and lutein. Based on the experimental results, a group of kinetic models describing cell growth, lutein production, and glucose and nitrogen consumption were proposed and a satisfactory fit was found between the experimental results and predicted values. Dynamic analysis of models demonstrated that enhancing initial nitrogen concentration in fermentor cultures, which correspondingly enhances cell growth and lutein formation, may shorten the fermentation cycle by 25–46%.