Induction of astaxanthin formation by reactive oxygen species in mixotrophic culture of Chlorococcum sp.

Abstract

The induction of astaxanthin formation by reactive oxygen species in mixotrophic culture of Chlorococcum sp. was investigated. H2O2 (0.1 mM) enhanced the total astaxanthin formation from 5.8 to 6.5 mg g-1 cell dry wt. Fe2+ (0.5 mM) added to the medium with H2O2 (0.1 mM) further promoted astaxanthin formation to 7.1 mg g-1 cell dry wt. Similarly, Fe2+ (0.5 mM) together with methyl viologen (0.01 mM) promoted astaxanthin formation to 6.3 mg g-1 cell dry wt. In contrast, an addition of KI (1 mM), a specific scavenger for hydroxyl radicals (OH•), together with H2O2 (0.1 mM) and Fe2+ (0.5 mM), to the medium decreased astaxanthin formation to 1.8 mg g-1 cell dry wt. KI (1 mM) also inhibited the enhancement of carotenogenesis by superoxide anion radicals (O2 -), with a decrease of astaxanthin formation to 1.7 mg g-1 cell dry wt. This suggested that O2 - might be transformed to OH• before promoting carotenogenesis in Chlorococcum sp.