| Hainan is located in tropic region with abundant ocean resources,which has warm climate, high annual rainfall all year-round and abundant water resources due to a number of lakes and rivers in the island. Thus, they can provide great nature conditions for bioprospecting of microalgal resources in Hainan. In this study, we have launched the isolation and screening of microalgae with high lipid content from Hainan province. Besides, the effects on properties of microalgal lipid-product and lipid accumulation have been investigated. And the main results were shown as follow:A total of89water samples were collected,178algal strains were obtained, among which110were freshwater microalgae, others are freshwater ones. Nile red fluorescence method and Bligh-Dyer method were used for selecting of rich lipids-microalgae, among them,14microalgae strains showed higher lipid productivities(greater than0.2g/L), the lipid productivities of C15, C29, C67, HK12were more than0.5g/L. Six species were identified by morphological observation and molecular classification as Chlorella sorokiniana Cl11.Chlamydomonas reinhardtii C22, Ourococcus sp. C24, Monoraphidium dybowskii C29, Chlorella zofingiensis HK12, and Micractinium reisseri C67.The biomass of those microalgal species were between0.5-8.0g/L. The highest biomass in C. zofingiensis HK12(with the average biomass of7.56g/L), the lowest biomass of these microalgal species was0.61g/L. The lipid contents of those microalgal species were between20-50%. The species Chla. Reinhardtii C22had high average lipid content of50%. The major fatty acids of the isolates were C16:0, C18:0, C16:1n-9, C18:1n-9, C16:2n-7, C18:2n-6, and C18:3n-3. C16:0, C18:0, and C18:ln-9existed as the most. The Micr. Reisseri C67, M. dybowskii C29, and C. zofingiensis HK12of the test strains were the most suitable for biodiesel production, because they were rich in oleic acid.The biomass productivity and lipid content in M. dybowskii C29, C. zofingiensis HK12, and Micr. reisseri C67were investigated under different trophic modes (autotrophy, mixotrophy and heterotrophy), different nitrogen, different concentration of phosphorus and different pH. The results indicated that, the three strains could be cultured in mixotrophy and hererotrophy, the mixotrophy was more fit for the growth and lipid accumulation. The three strains could be cultured in BG-11medium with ammonia, urea, and nitrate. The best nitrogen source for the test strains(M. dybowskii C29, C. zofingiensis HK12, Micr. reisseri C67) was sodium nitrate, urea, and ammonium chloride. The test strains grew slowly in low level of nitrogen, but the content of oils was high. The most optimum concentration of phosphorus were3.5and7-14mg/L for the biomass productivity and lipid content of M. dybowskii C29and C. zofingiensis HK12, respectively. The higher concentration would promote the growth of Micr. reisseri C67cells to produce more biomass, but would not conducive to lipid accumulation. Different pH values had great influence on the cells growth. M. dybowskii C29, C. zofingiensis HK12, and Micr. reisseri C67cells could grow under the experimental pH ranging from5to11,4.5to9.5, and4.5to11, respectively, and the cells would soon die When pH exceeded the range.M. dybowskii C29was cultivated in pail(outdoor). The biomass of this microalgal specie was between0.5-1.5g/L. Aimed to investigate the flocculating effect of three kinds of flocculants on M. dybowskii C29. The results showed that chitosan showed higher flocculating velocity. For flocculating100%of algae cells, at least0.04g/L of chitosan was required.Based on the results above, we draw a conclusion that M. dybowskii C29、C. zofingiensis HK12and Micr. reisseri C67all have the potential for biodiesel producing. |
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