Studies On The Inhibition Activity Of Ulva Intestinalis On Red Tide Microalgae And The Isolation And Identification Of The Algicidal Compounds

Frequent occurrence of harmful algal blooms(HAB) in world-wide caused great loss of mariculture and posed a serious threat to human health. At present, controlling of HAB includes physical methods such as ultrasonic, chemistry methods such as coagulating precipitation and the microorganism methods by using bacterium and virus. However, these methods were reported to have potential of disastrous environmental consequences. As a new developed method, HAB control by macroalgae has a broad research and application prospect because of its low cost and environmentally benign. In order to make full use of macroalgae to control HAB , twenty one kinds of seaweed samples collected from Zhejiang coast were screened for the algicidal activity against red tide microalgae, the algicidal activity of Ulva intestinalis on red tide microalgae and the algicidal compounds has also been studied, the results in detail were as follows:(1)U. intestinalis and Ulva lactuca. of Chlorophyta, Chondria crassicaulis, Grateloupia ramosissima and Gracilaria verrucosa of Rhodophyta showed the strongest algicidal activity among the seaweeds tested. More than 0.3 mg/mL of the extracts could inhibit the HAB microalgae Heterosigma akashiwo.(2) The inhibition effect of the dry powder, water extracts and ethyl acetate extracts of U. intestinalis were tested for their algicidal activities against Prorocenrum micans and Heterosigma akashiwo. The results indicated that the dry powder, water extracts and EtOAc extracts can inhibit the growth of red tide microalgae, and the inhibition activities increased along with the concentration increased. The concentrations of the water and EtOAc extracts respectively achieved above 0.96 mg/mL and 0.32 mg/mL could kill the P. micans. The concentrations of dry powder and EtOAc extracts respectively achieved above 1.2 mg/mL and 0.04 mg/mL could kill the H. akashiwo. This research also further confirmed that there are algicidal compounds exists in the macroalgae U. intestinalis.(3) Three active compounds were isolated from the EtOAc extract of U. intestinalis by the bioactivity-guided assay and silica gel column chromatography, Sephadex LH-20 chromatography, thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The structures were elucidated by1H-nuclear magnetic resonance (NMR), 13C-NMR spectral analysis, high resolution-mass spectrometry, ultraviolet, infrared spectrum and their physicochemical properties. The compounds purified were identified as 15- ethoxy-(6z,9z,12z) - hexadecatrienoic acid(Ⅰ), (6E,9E,12E)-(2-acetoxy -β-D-glucose)- octadecatrienoic acid ester(Ⅱ) and hexadecanoic acid(Ⅲ). All of the compounds showed algicidal activity on H. akashiwo and P. micans. The inhibition rate of compoundⅠat a dose of 20μg/mL in medium on H. akashiwo was 43.62%, and the inhibition rate on P. micans was 28.83%; The inhibition rate of compoundⅡat a dose of 20μg/mL in medium on H. akashiwo was 93.46%, and the inhibition on P. micans was 43.3%; The inhibition of compoundⅢat a dose of 50μg/mL in medium on H. akashiwo was 52.78%, and the inhibition on P. micans was 45.60%. Three active compounds are isolated from the U.intestinalis for the first time and 15- ethoxy-(6z,9z,12z) - hexadecatrienoic acid and(6E,9E,12E)-(2-acetoxy -β-D-glucose)- octadecatrienoic acid ester are new compounds.