Growth Inhibition of Two Typical Red Tide Microalgae (Karenia mikimitoi and Alexandrium tamarense) by Antialgal Substances from Gracilaria lemaneiformis and its Isolation and Identification

A yellow-brown extract (GLME) was obtained by methanol extraction of powder from Gracilaria lemaneiformis. The methanol extract was further fractionated by liquid-liquid extraction and obtained the four fractions (F-Ⅰ, F-Ⅱ, F-Ⅲ and F-Ⅳ). Growth inhibition of two typical red tide microalgae (Karenia mikimitoi and Alexandrium tamarense) by those fractions and its isolated fractions were investigated. The results showed that crude extract had inhibitory activity against the growth of Karenia mikimitoi and Alexandrium tamarense. Among the four fractions, F-Ⅱ exhibited the strongest effect against the growth of the two red tide microalgae, and the inhibitory effect of Karenia mikimitoi and Alexandrium tamarense by F-Ⅱ at the concentration of 0.35 g/L was 48.8% and 46.7% in day 12, respectively. After additional isolation of F-II with five organic solvents (petroleum ether, petroleum ether:ethyl acetate=1:1, ethyl acetate, ethyl acetate:acetone=1:1 and acetone), the F- II was separated into five fractions of Ⅱ-A, Ⅱ-B, Ⅱ-C, Ⅱ-D and Ⅱ-E on silicon gel column, respectively. The eluant Ⅱ-B andⅡ-C showed the significant growth inhibition activities. The antialgal substances in eluant Ⅱ-B andⅡ-C are identified by comprehensive analysis of UV and HPLC-MS to be chlorogenic acid, hydroxybenzoic acid and vanillic acid. And they significantly inhibited the growth of Karenia mikimitoi and Alexandrium tamarense.