Composition and accumulation of secondary carotenoids in Chlorococcum sp.

A locally isolated Chlorococcum sp. could accumulate astaxanthin and its esters as secondary carotenoids. The secondary carotenoids could reach a concentration of 5.2 mg g(-1) d. wt, and were located in the cytoplasm and chloroplast as globules. Cells grew best at pH 8.0 and 30 degrees C, at which the growth rate was about 0.066 h(-1) Acidic condition (pH 5.5 and 6.5) and slightly elevated temperature (35 degrees C) enhanced the cellular accumulation of astaxanthin. Outdoor studies indicated that Chlorococcum sp, grew well in a tubular photobioreactor. In medium containing 2 mM and 10 mM NH4CI, the cellular contents of total secondary carotenoids and astaxanthin reached similar levels (5.0 mg g(-1) d. wt and 2.0 mg g(-1) d. wt, respectively) in the 15 days of cultivation, while the yields of total secondary carotenoids and astaxanthin in 10 mM NH4CI were higher (45 mg L-1 and 18 mg L-1, respectively). The advantages of tolerance to high temperature and extreme pH values, relative fast growth rate and ease of cultivation in an outdoor system suggest that Chlorococcum sp. could be a potential candidate for mass production of secondary carotenoids in particular astaxanthin.