Effects of Ascophyllum nodosum extract on growth and antioxidant defense systems of two freshwater microalgae

摘要

Microalgae in genus Chlorella and Scenedesmus are common in aquatic ecosystems and are widely used for various studies on algal growth and applications. Macroalgae may play an important role for control of microalgal growth, attributable to their rich content of bioactive compounds. In this study, the brown seaweed Ascophyllum nodosum was extracted with 70% acetone and the extract was used to treat the green microalgae, Chlorella vulgaris and Scenedesmus sp. Cell density and chlorophyll a concentration were used as growth indexes to evaluate the effects of A. nodosum extract (ANE) on the microalgae. The ANE with concentrations & 1% exhibited significant capability of inhibition of the growth of microalgae by over 80%. On the contrary, 1% ANE caused varying degrees of acceleration of cell proliferation and chlorophyll a synthesis in C. vulgaris and Scenedesmus sp., respectively. Analysis of antioxidant activities of the enzymes superoxide dismutase (SOD) and catalase (CAT) revealed the impact of ANE on the antioxidant defense system of the microalgae. The SOD and CAT activities were significantly depressed by high concentrations (& 2%) ANE, while a slight increase of the enzyme activities was observed with 1% ANE at the early period, which could be correlated to the growth response. Therefore, the mechanism of microalgae control could be related to the interaction between the ANE and the antioxidant defense systems. Phlorotannins are proposed as the principal algistatic components in the ANE which could be utilized in controlling microalgae growth.