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Biosynthesis of Astaxanthin in Haematococcus Pluvialis under Zinc, Copper and Iron Metal Stresses

Abdolmajid Lababpour, department of Biotechnology, Inha University, 253 Younghyun-dong, Nam-gu,, Incheon 402-751, Korea, Incheon, South Korea

Statistical optimization for maximum production of astaxanthin by central composite design method was investigated. The fermentation variables optimized by 'one variable at a time' approach were further optimized by response surface methodology (RSM). The statistical model was obtained using central composite design (CCD) with three variables: copper, iron and zinc concentration. An overall 24 and 70% increase in astaxanthin production was attained in shake flasks and column photobioreactor because of optimization by RSM, respectively. RSM allowed optimization of medium components and cultural parameters for attaining high yields of astaxanthin, and further, a good coverage of interactions could be explained. Exposure of Haematococcus pluvialis to Cu or Zn enhanced intracellular levels of both test metals and astaxanthin. The level of intracellular astaxanthin increased markedly up to 10 M Cu, but higher concentrations were inhibitory. However, intracellular astaxanthin consistently increased with increasing concentration of Zn in the medium. Cu and Zn induced oxidative stress in the test alga by increasing cell astaxanthin content. Interestingly, green cells absorbed more metals (Cu 2554%, Zn (1949%) compared to red cells with the same cell productivity. The cell viability decreased in high concentrations of Cu and Zn metals by 30%. A comparison of the effects of increment of Cu, Zn, and mixture of Cu-Zn metals suggests that astaxanthin protects cells from metal-induced oxidative stress. Pretreatment of cells with a known antioxidant (ascorbate) and a hydroxyl radical scavenger (sodium benzoate) considerably reduced metal-induceduction and astaxanthin accumulation in H. pluvialis cells. The present study demonstrates that higher concentration of non toxic metals of Cu, Zn and mixture of metals is effective in improving the antioxidant defense system under metal stress and induction of astaxanthin in the cells.