The Study On Screening Of Anti-microbial Activities, Isolation And Purification Of Antibacterial Substances From Marine Microalgaes

Drug-resistance of microorganisms has becoming one of the factors threatening the health of human in 21 century. Therefore, exploiting new anti-microbial compounds is emergent. The research on microalgaes and its metabolisms is becoming hot topic around the world recently. In this article, we mainly study the anti-microbial activities of different solvent extracts of 10 microalgaes using agar diffusion method, optimizing the cultural conditions, isolation and purification of the target microalgae.The anti-microbial activities of differently solvent extracts from nine microalgaes were investigated in this article, via agar diffusion method. The results showed that: (1) Different solvent extracts from ten microalgaes indicated different degrees of anti-microbial activities against tested microorganisms. Especially, Isochrysis galbana Parke H₂₉, Isochrysis galbana Parke 8701, Isochrysis galbana Parke 3011, Chaetoceros muelleri, Chlorella pyrenoidosa Chick and Platymonashelgolandica var Tsingtaoensis showed considerable and wide spectum anti-microbial activities. Otherwise, the exploitation of these microalgaes is potentially valuable for the simple nutritional needs and easily cultured in photobioreactor. (2)In all the samples, 66.67% of the extracts showing antibacterial activity against Staphylococcus aureus exhibited the antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). In special, Isochrysis galbana Parke H₂₉, Chaetoceros muelleri, Chroommonas salina, Isochrysis galbana Parke 8701 and Platymonashelgolandica var Tsingtaoensis indicated considerable activities against MRSA, which proving that these microalgaes may be a new potential sources of anti-MRSA substances.(3) The acetone extracts of Isochrysis galbana Parke H₂₉ indicated considerable activities against standard Staphylococcus aureus, Bacillus subtilis and Escherichia coli. Moreover, the activity of acetone extracts of Isochrysis galbana Parke H₂₉ against methicillin-resistant Staphylococcus aureus is equal to half of that of vancomycin HCL (48μg/mL) , which proving that exploiting the antibacterial compounds from Isochrysis galbana Parke H₂₉ has broad foreground.At present, the cell concentration of culturing Isochrysis galbana Parke H₂₉ is so low that its bioactive compounds could not be easily isolation and preparation. Therefore, based on the f/2 medium, the culture conditions of the microalgae were optimized in this article. The results showed that: (1) Optimum culture conditions of Isochrysis galbana Parke H₂₉ were that temperature was 25℃, illumination intensity 5000 Lux and pH 8. (2) The better medium formula for the growth of the Isochrysis galbana Parke H₂₉ was using NaNO₃ as nitrogen with the optimum growth concentration of 37.5 mg/L, NaH₂PO₄ as phosphor with the optimum growth concentration of 4.4 mg/L and FeC₆H₅O₇ as iron with the optimum growth concentration of 3.9g/L. The best growth concentration of NaCl was 23 g/L. The rest nutrition are the same with the f/2.Based on the acetone extracts of Isochrysis galbana Parke H29, two anti-microbial substances, named as L1 and L2, were isolated, via extracting and reduplicate column-chromatography. The results showed that L1 exhibited antibacterial activity against MRSA, and its MIC is 150μg/mL. L2 exhibited antibacterial activity against MRSA and E.coli, and its MIC are 100μg/mL and 10μg/mL, respectively. According to the analysis of UV and HPLC-ESI-MS, L1 may be quinines, molecular weight of L2 is 274, and L2 may be sulphuric ether. However, the structures of L1 and L2 should be further studied.