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Switching cultivation (mixotrophic-heterotrophic, 12h:12h) of Heynigia riparia SX01 was studied, the maximum biomass concentration of 3.55gL-1 and lipid yield of 1.45gL-1 were achieved after 8days cultivation. The extracellular polymeric substance (EPS) was developed as co-product. Addition of MgSO4 could enhance the production of EPS. The highest amount of 0.60gL-1 EPS was obtained with the addition of 2gL-1 MgSO4, the self-flocculation efficiency was as high as 83% at this condition. The total lipid and lipid fractions did not show differences with extra MgSO4. Based on the above results, a new biodiesel production model was proposed: culturing Heynigia riparia SX01 with extra 2gL-1 MgSO4 by switching cultivation and using self flocculation to collect microalgae for biodiesel production, while EPS was collected as valuable co-products.

Alkaline environments are abundant globally and cause damage to most organisms, while some microalgae can grow well and accumulate lipids under those conditions. Here the mechanisms of alkali resistance and lipid accumulation in the alkaliphilic microalgae Chlorella sp. BLD were explored using physiological-biochemical and transcriptome analysis. When cultivated at alkaline pH, Chlorella sp. BLD exhibited good alkali-resistance ability and increased biomass (0.97 g L−1). The biochemical composition of Chlorella sp. BLD changed significantly (lipid content increased 39% and protein content decreased 19.5%) compared with pH 7.5. Through transcriptome analysis, we found that pathways related to carbon metabolism such as photosynthesis, glycolysis, and the TCA cycle were significantly regulated under alkaline conditions. Genes that encoding the key enzyme in carbon-related metabolism such as Rubisco, AMY, PK, ME, CS, ACAT, KAS, and DGAT were identified. Transcriptional regulation of these genes results in carbon flow switching from starch and protein to cell wall metabolism, organic acid synthetic and lipid accumulation in response to alkaline conditions. These results reveal the alkali resistance mechanism of Chlorella sp. BLD and provide a theoretical basis for microalgae oil production under alkaline conditions.

Biodiesel quality associated with biochemical components of Chlorella pyrenoidosa and Scenedesmus obliquus under different nitrate levels were investigated. The highest lipid contents of 54.5% for C. pyrenoidosa and 47.7% for S. obliquus were obtained in nitrate absence. Carbohydrate peaked at 0.3gL(-1) with values of 40.7% for C. pyrenoidosa and 42.5% for S. obliquus. Protein content seemed species dependent, which decreased substantially to 11.2% in C. pyrenoidosa and 8.8% in S. obliquus under nitrate absence in present research. Better biodiesel quality (e.g. cetane number58, iodine value69) could be obtained from C. pyrenoidosa in nitrate absence and S. obliquus in 0.3gL(-1), where the highest saturated fatty acids (39.5 for C. pyrenoidosa, 31.2 for S. obliquus) and the lowest unsaturated fatty acids (60.5 for C. pyrenoidosa, 68.8 for S. obliquus) were obtained. These results suggest that microalgae grown in the presence of nitrogen may limit biodiesel quality.

Organisms use various adaptive strategies against phosphate stress, including lipid remodeling. Here, the response of major membrane lipids to phosphate stress was analyzed in Synechococcus sp. PCC 7942. Unlike plants and eukaryotic microalgae, no significant increases in neutral lipids were found, whereas glycolipids content increased to as high as 6.13% (of dry cell weight, DCW) and phospholipids decreased to 0.34% (of DCW) after 16 days of cultivation without phosphate. Glycolipids accumulation were mainly attributed to the significant increase of digalactosyldiacylglycerol (DGDG) by 50% and sulfoquinovosyldiaclglycerol (SQDG) by 90%, both of which acted as complementary lipids for phosphatidylglycerol (PG) in the cyanobacterial membrane. Also, a notable increase in content (by 48%) of C18 fatty acids (especially C18:1) was observed in all glycolipids at the expense of C12 and C14 (72%). These changes may contribute to membrane fluidity and photosynthetic activity for basic cell metabolism and phosphate stress adaptation. Lipidomic analyses showed the reduction of PG 18:1/16: 0 (by 52%) with the increase of DGDG 18:1/16:0 (133%) and SQDG 18:1/16:0 (245%), strongly suggesting a direct conversion of PG to DGDG and SQDG. Moreover, the decreasing amount of monogalactosyldiacylglycerol (MGDG) 16:1/16:0 (22%) was consistent with the increase of free fatty acids (125%) on day 2 of phosphate absence, which suggested that MGDG is more likely to provide a pool of fatty acids for de novo synthesis of glycolipids. This study provides valuable insight into cyanobacteria adaptation strategies to phosphate stress by membrane lipid remodeling and unveils the underlying acyl chain fluxes into glycolipids.

Haematococcus pluvialis is one of the most abundant sources of natural astaxanthin as compared to others microorganism. Therefore, it is important to understand the biorefinery of astaxanthin from H. pluvialis, starting from the cultivation stage to the downstream processing of astaxanthin. The present review begins with an introduction of cellular morphologies and life cycle of H. pluvialis from green vegetative motile stage to red non-motile haematocyst stage. Subsequently, the conventional biorefinery methods (e.g., mechanical disruption, solvent extraction, direct extraction using vegetable oils, and enhanced solvent extraction) and recent advanced biorefinery techniques (e.g., supercritical CO2 extraction, magnetic-assisted extraction, ionic liquids extraction, and supramolecular solvent extraction) were presented and evaluated. Moreover, future prospect and challenges were highlighted to provide a useful guide for future development of biorefinery of astaxanthin from H. pluvialis. The review aims to serve as a present knowledge for researchers dealing with the bioproduction of astaxanthin from H. pluvialis.

The aim of this work was to study salt stress effects on DNA content and oil production processes integrating harvesting, lipid accumulation and oil extraction. Salt-induced enlargement of Parachlorella kessleri cells, with increasing content of DNA and neutral lipid were found. The 34.77% neutral lipid content and biomass concentration of 0.83 g L−1 were obtained after 7 days of salt treatment, compared with that of 13.57% and 0.89 g L−1 cultivated under normal condition. Sedimentation efficiency increased markedly from 15% to 90% due to the cell enlargement. Disruption fraction and the recovery rate of total lipids of wet cells under salt stress were significantly higher than that of normal conditions (100% and 82.4% for salt stress vs.76.8% and 51.1% for normal conditions). This work demonstrated that salt-induced increase in cell size and DNA content was an effective strategy for the enhancement of oil production, microalgae harvesting and oil extraction.

High effective acidic transesterification catalyzed by trifluoroacetic acid for biodiesel production was studied in the present research. The results showed that the oil could be converted to biodiesel directly by one-step trifluoroacetic acid catalyze process without extreme temperature and pressure conditions. The optimum process combination was 2.0 M catalyst concentration with 20:1 M ratio of methanol to oil at temperature of 120 °C. It reduced product specific gravity from an initial value of 0.965 to a value of 0.878 in about 5 h of reaction time, and the methyl ester content reached as high as 98.4%. The present procedure represents a simple and mild method for biodiesel production in short reaction time and with high conversion rate, which would offer potential for an industrial process.

In this paper, statistical Plackett–Burman design and Box–Behnken Response Surface Methodology were applied to optimize the medium components to improve the chitinase activity of Streptomyces sp. DA11 associated with South China Sea sponge Craniella australiensis. Firstly, galactose and peptone were found to be the suitable carbon and nitrogen sources for the growth and chitinase activity by single factor Seriatim–Factorial test. Secondly, galactose, colloidal chitin and MgSO4� 7H2O were proved to have remarkable effects on chitinase activity. Finally, an optimal medium was obtained by Box–Behnken

The aim of the study was to obtain high quality biodiesel production from a microalga Chlorella protothecoids through the technology of transesterification. The technique of metabolic controlling through heterotrophic growth of C. protothecoides was applied, and the heterotrophic C. protothecoides contained the crude lipid content of 55.2%. To increase the biomass and reduce the cost of alga, corn powder hydrolysate instead of glucose was used as organic carbon source in heterotrophic culture medium in fermenters. The result showed that cell density significantly increased under the heterotrophic condition, and the highest cell concentration reached 15.5 g L(-1). Large amount of microalgal oil was efficiently extracted from the heterotrophic cells by using n-hexane, and then transmuted into biodiesel by acidic transesterification. The biodiesel was characterized by a high heating value of 41 MJ kg(-1), a density of 0.864 kg L(-1), and a viscosity of 5.2 x 10(-4) Pa s (at 40 degrees C). The method has great potential in the industrial production of liquid fuel from microalga.

In the present study, fast pyrolysis tests of microalgae were performed in the fluid bed reactor. The experiments were completed at temperature of 500 degreesC with a heating rate of 600 degreesC s(-1) and a sweep gas (N-2) flow rate of 0.4 m(3) h(-1) and a vapour residence time of 2-3 s. In comparison with the previous studies on slow pyrolysis from microalgae in an autoclave, a greater amount of high quality bio-oil can be directly produced from continuously processing microalgae feeds at a rate of 4 g min(-1) in the present work, which has a potential for commercial application of large-scale production of liquid fuels. The liquid product yields of 18 and 24% from fast pyrolysis of Chllorella protothecoides and Microcystis aeruginosa were obtained. The saturated and polar fractions account for 1.14 and 31.17% of the bio-oils of microalgae on average, which are higher than those of bio-oil from wood. The H/C and O/C molar ratios of microalgae bio-oil are 1.7 and 0.3, respectively. The gas chromatograph analyses showed that the distribution of straight-chain alkanes of the saturated fractions from microalgae bio-oils were similar to diesel fuel. Bio-oil product from fast pyrolysis microalgae is characterized by low oxygen content with a higher heating value of 29 MJ/kg, a density of 1.16 kg l(-1) and a viscosity of 0.10 Pa s. These properties of bio-oil of microalgae make it more suitable for fuel oil use than fast pyrolysis oils from lignocellulosic materials. (C) 2003 Elsevier B.V. All rights reserved.

The use of renewable energy sources is becoming increasingly necessary to mitigate global warming. Recently much research has been focused on identifying suitable biomass species, which can provide high-energy outputs, to replace conventional fossil fuels. This paper reports an approach for increasing the yield of bio-oil production from fast pyrolysis after manipulating the metabolic pathway in microalgae through heterotrophic growth. The yield of bio-oil (57.9%) produced from heterotrophic Chlorella protothecoides cells was 3.4 times higher than from autotrophic cells by fast pyrolysis. The bio-oil was characterized by a much lower oxygen content, with a higher heating value (41 MJ kg(-1)), a lower density (0.92 kg l(-1)), and lower viscosity (0.02 Pas) compared to those of bio-oil from autotrophic cells and wood. These properties are comparable to fossil oil. The research could contribute to the creation of a system to produce energy from microalgae, and also could have great commercial potential for liquid fuel production.