Isolation And Purification Of Antimicrobial Components From Microalgae

The limitation of antibiotic resistance on the effects of traditional antibiotics proves the necessity of exploiting new antimicrobial compounds from natural products. Rich in bioactive substances, marine microalgae have become an important potential drug resource for its special growing environment. Otherwise, these microalgae are with exploitation value for their simple nutritional needs and easy cultured.In this article, we investigated the antimicrobial activities of 22 kinds of microalgae using agar diffusion method, and screened Chaetoceros curvisetus as the target microalgae. The main experimental results were as follows:The extracts from 22 kinds of microalgae presented different antimicrobial activities against tested microorganisms, and Chaetoceros curvisetus showed the strongest activity. The crude lipid, polyphenols and terpenoids of Chaetoceros curvisetus all inhibited the microorganism growth by different degrees, which proving the priming exploitation future of antibacterial compounds from Chaetoceros curvisetus. The microalgae extract all inhibited bacteria more strongly than fungi.The petroleum ether extract of Chaetoceros curvisetus had the broadest antibacterial activity among fat-soluble extracts by different polarity solvents. In order to identify the compounds contributing to the antimicrobial activity, gas chromatography characterization of different polar lipid extracts were performed. Polyunsaturated fatty acids such as linolelaidic acid,γ-linolenic acid, cis-11, 14-eicosadienoic acid et al were specially found in the petroleum ether extract, which indicated that the antibacterial compounds were mainly the weak-polar polyunsaturated fatty acids. The petroleum ether extract was separated by silica gel column chromatography into four kinds of components. The antimicrobial activity of crude fat was generally stronger than the four separated components. It is possibly that the antibacterial activity depended on the variety of aliphatic compounds, or the antibacterial activities of other compounds were lost during chromatography, drying and processing through various solvents.In addition, the extract conditions of polyphenols from Chaetoceros curvisetus were optimized, and the optimum one is as follows: 80% ethanol as extracting solvent with a solid/solvent ratio of 1:15(w/v), and extracting 3 times each for 40 minutes each. AB-8 was selected as the medium for initial isolation of polyphenols by comparing the adsorption and separation performances of 8 kinds of macroporous adsorption resins, and the adsorption capacity of AB-8 was valued as 80.1%. The optimum adsorption and separation conditions for the crude extract on AB-8 macroporous adhesive resin column were confirmed as follows: the feed concentration of 3 mg/mL with flow rate of 2 mL/min, and the desorption solvent 70% ethanol with flow velocity of 4 mL/min.CP was divided into 2 kinds of bioactive fractions (CPC-1 and CPC-2) after gel silica column chromatography and Sephadex LH-20. All bioactive fractions were compared in each purification process and CPC-2 showed the strongest antibacterial activity. At the concentration of 1 mg/mL, the inhibitory zone of Bacillus subtilis and Staphylococcus aureus was 14.0±0.5 mm, and the inhibitory zone of Escherichia coli and Proteas valgaris could reach to 16.0±0.8 mm, and the antifungal activity was also increased. CPC-2 was identified as 3,4,5-trihydroxy benzoic acid.