Production potential of Chlorella zofingienesis as a feedstock for biodiesel.

The lipid contents and fatty acid profiles of Chlorella zofingiensis cultured in the dark with various carbon sources were investigated. Glucose was found to be the best carbon source for the growth and lipid production. When cultivated with 50gL(-1) glucose, C. zofingiensis accumulated lipids up to 52% of the dry biomass, with triacylglycerols (TAGs) accounting for 72.1% of the total lipids. Fatty acid profiles revealed that glucose contributed to the highest yield of total fatty acids (TFAs) and proportion of oleic acid (35.7% of TFAs), which corresponded to the strongest up-regulation of biotin carboxylase (BC) and stearoyl ACP desaturase (SAD) genes. In fed-batch cultivation based on glucose, the lipid yield and productivity of C. zofingiensis were further increased to 20.7gL(-1) and 1.38gd(-1)L(-1) respectively, representing 3.9-fold of those achieved in batch culture. We conclude that C. zofingiensis has great potential for biodiesel production.

Optimization of nitrogen source for enhanced production of squalene from thraustochytrid Aurantiochytrium sp.

Nitrogen (N) sources, the critical medium component, were optimized for squalene production by microalga Aurantiochytrium sp. in heterotrophic cultures. In screening experiments monosodium glutamate, yeast extract and tryptone were found to enhance cell growth and squalene production. The optimal levels of the three nitrogen sources were further determined through central composite experimental design. The squalene content and yield were both influenced not only by monosodium glutamate, tryptone and yeast extract, but also by their interactions. The squalene content and squalene yield were described by the second-order polynomial equations with high confidence levels (>99%). The optimal concentrations of monosodium glutamate, yeast extract and tryptone were predicted to be 6.61 g/L, 6.13 g/L and 4.50 g/L for squalene content and 6.94 g/L, 6.22 g/L and 4.40 g/L for squalene yield, respectively. In the verification experiment, the squalene content and squalene yield reached 0.72 mg/g and 5.90 mg/L, respectively, which were much higher than those obtained in previous studies.

Enhanced production of squalene in the thraustochytrid Aurantiochytrium mangrovei by medium optimization and treatment with terbinafine.

Squalene is an effective chemopreventive agent in reducing the incident of coronary heart disease and cancer. It is also a strong antioxidant used extensively in the food and cosmetic industries. Microbial sources of squalene are being explored in recent years. The objective of this study is to increase the squalene content and yield in the thraustochytrid, Aurantiochytrium mangrovei FB3 through medium optimization and the treatment with terbinafine, an inhibitor of squalene monooxygenase in the sterol biosynthetic pathway. The highest biomass concentration of 21.2 g l(-1) was obtained at a glucose concentration of 60 g l(-1), while the highest specific growth rate of 0.077 h(-1) and the growth yield coefficient of 0.44 g g(-1) based on glucose were achieved at a lower glucose concentration (30 g l(-1)). The addition of terbinafine led to a slight inhibition of cell growth whereas an obvious increase in squalene content was observed at terbinafine concentrations of 10 and 100 mg l(-1), which corresponded to an increase of 36 and 40% in squalene content, respectively compared to the control. The addition of terbinafine was thus effective in inducing the accumulation of squalene in A. mangrovei. This study not only demonstrated the production potential of squalene by A. mangrovei, but also provided novel information on the accumulation effect of terbinafine on the biosynthesis of an essential intermediate involved in sterol metabolic pathway.

Differentiation in fatty acid profiles of pigmented and nonpigmented Aurantiochytrium isolated from Hong Kong mangroves.

Twenty-five thraustochytrids that belong to the genus Aurantiochytrium were isolated from subtropical mangroves in Hong Kong. Although they have similar morphological and physiological characteristics, they have different colors on a yeast extract-glucose agar plate, which were largely ignored before. On the basis of the differences in their colony color, 25 Aurantiochytrium strains were further classified into pigmented and nonpigmented subgroups and their fatty acid profiles were analyzed and compared. In general, nonpigmented Aurantiochytrium strains were found to contain biomass concentrations and growth yield coefficients statistically higher than pigmented Aurantiochytrium strains (p < 0.01). Among all isolates, a significantly higher content of polyunsaturated fatty acid (PUFA, 123.41-179.64 mg/g) was found in the nonpigmented Aurantiochytrium (p < 0.01), whereas the pigmented strains contained a higher amount of saturated fatty acids. Docosahexaenoic acid (DHA) was identified as the most abundant PUFA in both nonpigmented and pigmented Aurantiochytrium. According to the result of principal component analysis, the contents and composition of saturated fatty acids and PUFAs are the major varieties to distinguish these two Aurantiochytrium groups, especially the contents of C15:0, C13:0, C16:0, C17:0, and DHA. With a rapid growth rate and high DHA yield, the strain from the nonpigmented Aurantiochytrium group was regarded as the ideal candidate for PUFA production.

Screening and characterization of squalene-producing thraustochytrids from Hong Kong mangroves.

Eighteen strains of thraustochytrids were newly isolated from Hong Kong mangroves, and their fatty acid and squalene contents were analyzed. All strains could grow well heterotrophically with glucose as the sole carbon source. All of them had the typical fatty acid profile of thraustchytrids and could produce a large amount of docosahexaenoic acid. The cell dry weight ranged from 5.49 to 15.62 g/L and squalene content from 0.02 to 0.18 mg/g at 72 h. The highest squalene-producing strain, BR-MP4-A1 was identified as a new strain of Aurantiochytrium species through sequence comparison of the 18S rRNA gene. The highest biomass of Aurantiochytrium sp. BR-MP4-A1 was achieved at 72 h, whereas its squalene content reached the maximum of 0.567 mg/g at 36 h but decreased rapidly thereafter. The production of squalene by thraustochytrids might be highly influenced by culture conditions.

Lipid characterization of mangrove thraustochytrid--Schizochytrium mangrovei.

Lipid class composition and distribution of fatty acids within the lipid pool of microalga, Schizochytrium mangrovei FB3 harvested at the late exponential phase, was studied, with special emphasis on the distribution of docosahexaenoic acid (C22:6 n-3, DHA). Neutral lipids were the major lipid constituents (95.90% of total lipids) in which triacylglyerol (TAG) was the predominant component and accounted for 97.20% of the neutral lipids. Phosphatidylcholine (PC) was the major polar lipid. Phosphatic acid and phosphatidylserine were the two classes in phospholipids reported for the first time in thraustochytrids. Both TAG and PC were primarily saturated and consisted of C16:0 at approximately 50% of total fatty acids. DHA was found to be distributed in all lipid classes and to be the major polyunsaturated fatty acid. TAG contained the highest amount of DHA, although the percentage of DHA in total fatty acids in TAG (29.74%) was lower than that in PC (39.61%). The result from this study would be useful for further optimization of DHA production by S. mangrovei.

Isolation and purification of canthaxanthin from the microalga Chlorella zofingiensis by high-speed counter-current chromatography.

Certain microalgae are considered to be a potential source of canthaxanthin, which possesses strong antioxidant and anticancer activities. A high-speed counter-current chromatography (HSCCC) method was developed for the separation and purification of canthaxanthin from the microalga Chlorella zofingiensis. The crude canthaxanthin was obtained by extraction with organic solvents after the microalgal sample had been saponified. Preparative HSCCC, with a two-phase solvent system composed of n-hexane-ethanol-water (10:9:1 v/v), was successfully performed yielding canthaxanthin at 98.7% purity from 150 mg of the crude extract (2.1% canthaxanthin) in a one-step separation. The recovery of canthaxanthin was 92.3%. This was the first report that canthaxanthin was successfully separated and purified from microalgae.

Fatty acid composition and squalene content of the marine microalga Schizochytrium mangrovei.

Certain species of thraustochytrids are being explored as potential producer of polyunsaturated fatty acids for nutritional enrichment of food products and use as feed additives in aquaculture. The fatty acid composition and squalene content were determined in the thraustochytrid, Schizochytrium mangrovei that was newly isolated from decaying Kandelia candel leaves in Hong Kong mangrove habitat. The major fatty acid constituents identified in all three S. mangrovei strains were tetradeanoic acid (C14:0), hexadecanoic acid (C16:0), docosapentaenoic acid (C22:5 n-6, DPA) and docosahexaenoic acid (C22:6 n-3, DHA). DHA was the most predominant polyunsaturated fatty acid, and the percentage of DHA (of total fatty acids) in all these strains varied from 32.29 to 39.14%. Only slight changes were observed in fatty acid composition of the S. mangrovei strains harvested at their early (day 3) and late stationary (day 5) phases. In contrast, the cellular squalene content was affected significantly by the culture time; the largest decrease of squalene content from 0.162 mg/g to 0.035 mg/g was found in S. mangrovei FB1 as the culture aged.