A quantitative study of eicosapentaenoic acid (EPA) production by Nannochloropsis gaditana for aquaculture as a function of dilution rate,temperature and average irradiance

Different pilot-scale outdoor photobioreactors using medium recycling were operated in a greenhouse under different environmental conditions and the growth rates (0.1 to 0.5 day^?1) obtained evaluated in order to compare them with traditional systems used in aquaculture. The annualized volumetric growth rate for Nannochloropsis gaditana was 0.26 g l^?1 day^?1 (peak 0.4 g l^?1 day^?1) at 0.4 day^?1 in a 5-cm wide flat-panel bioreactor (FP-PBR). The biomass productivity achieved in this reactor was 10-fold higher than in traditional reactors, reaching values of 28 % and 45 % dry weight (d.w.) of lipids and proteins, respectively, with a 4.3 % (d.w.) content of eicosapentaenoic acid (EPA). A model for predicting EPA productivity from N. gaditana cultures that takes into account the existence of photolimitation and photoinhibition of growth under outdoor conditions is presented. The effect of temperature and average irradiance on EPA content is also studied. The maximum EPA productivity attained is 30 mg l^?1 day^?1.     

The effects of cultivation depth,areal density,and nutrient level on lipid accumulation of <Emphasis Type="Italic">Scenedesmus acutus</Emphasis> in outdoor raceway ponds

Lipid accumulation is critical in the production of biodiesel from microalgae. However, little work has been done on the assessment of lipid accumulation during nitrogen stress in large research-scale outdoor raceways during different seasons; most values for lipid accumulation are assumptions based on work completed in laboratory settings or outdoor photobioreactors. This study focused on the use of raceway ponds operated in batch cultivation mode with an area of 30.37 m² to determine the impacts of nitrate-nitrogen concentration and cultivation depth on the ability of Scenedesmus acutus strain LB 0414 to accumulate lipids. A concentration of less than 60 mg N-NO₃ ^??L^?1 was required for removal of nitrogen in the cultivation medium within 8 days to stimulate lipid accumulation and increase lipid productivity. When nitrate concentrations were increased to prevent nitrogen depletion, lipid productivity decreased, which demonstrates that stressing is needed to induce lipid accumulation for increased lipid productivity. Additionally, decreasing cultivation depth below 9 cm, compared to raceways operated at a depth of 20–24 cm, increased lipid productivity by 62 % in December 2014 and 38 % in February 2015. More desirable environmental conditions, mainly increased sunlight and temperature, in February, increased biodiesel productivity for all raceways and account for the decrease in productivity differences. This research highlights increased lipid productivity found by reducing cultivation depth and nitrogen concentrations in outdoor raceways and provides insight into the optimal conditions for large-scale biodiesel production.     

Screening Microalgae Strains for Biodiesel Production: Lipid Productivity and Estimation of Fuel Quality Based on Fatty Acids Profiles as Selective Criteria

The viability of algae-based biodiesel industry depends on the selection of adequate strains in regard to profitable yields and oil quality. This work aimed to bioprospecting and screening 12 microalgae strains by applying, as selective criteria, the volumetric lipid productivity and the fatty acid profiles, used for estimating the biodiesel fuel properties. Volumetric lipid productivity varied among strains from 22.61 to 204.91 mg l^?1 day^?1. The highest lipid yields were observed for Chlorella (204.91 mg l^?1 day¹) and Botryococcus strains (112.43 and 98.00 mg l^?1 day^?1 for Botryococcus braunii and Botryococcus terribilis, respectively). Cluster and principal components analysis analysis applied to fatty acid methyl esters (FAME) profiles discriminated three different microalgae groups according to their potential for biodiesel production. Kirchneriella lunaris, Ankistrodesmus fusiformis, Chlamydocapsa bacillus, and Ankistrodesmus falcatus showed the highest levels of polyunsaturated FAME, which incurs in the production of biodiesels with the lowest (42.47–50.52) cetane number (CN), the highest (101.33–136.97) iodine values (IV), and the lowest oxidation stability. The higher levels of saturated FAME in the oils of Chlamydomonas sp. and Scenedesmus obliquus indicated them as source of biodiesel with higher oxidation stability, higher CN (63.63–64.94), and lower IV (27.34–35.28). The third group, except for the Trebouxyophyceae strains that appeared in isolation, are composed by microalgae that generate biodiesel of intermediate values for CN, IV, and oxidation stability, related to their levels of saturated and monosaturated lipids. Thus, in this research, FAME profiling suggested that the best approach for generating a microalgae-biodiesel of top quality is by mixing the oils of distinct cell cultures.     

Effects of photoperiod,salinity and pH on cell growth and lipid content of Pavlova lutheri

The aim of the present work was to study the effects of photoperiod, salinity and pH on growth and lipid content of Pavlova lutheri microalgae for biodiesel production in small-scale and large-scale open-pond tanks. In a 250-mL flask, the cultures grew well under 24 h illumination with maximum specific growth rate, μ _max , of 0.12 day^?1 and lipid content of 35 % as compared to 0.1 day^?1 and 15 % lipid content in the dark. The salinity was optimum for the cell growth at 30–35 ppt, but the lipid content of 34–36 % was higher at 35–40 ppt. Algal growth and lipid accumulation was optimum at pH 8–9. Large-scale cultivation in 5-L and 30-L tanks achieved μ _max of 0.13–0.14 day^?1 as compared to 0.12 day^?1 in small-scale and 300L cultures.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

Triacylglycerol content,productivity and fatty acid profile in Scenedesmus acutus PVUW12

A detailed lipid characterization of Scenedesmus acutus PVUW12, with emphasis on the evaluation of triacylglycerols (TAGs) as a biodiesel feedstock, is presented. When algal cells were grown in nitrogen-free medium (N stress), a lipid increase was detected that was mainly due to TAG accumulation. In situ fluorescence measurements allowed the kinetics and extent of neutral lipid accumulation to be followed. Under N stress, the productivity of total lipids and TAGs increased significantly (80.99 and 63.74 mg L^?1 day^?1, respectively) compared with controls (29.51 and 16.23 mg L^?1 day^?1, respectively). Monounsaturated fatty acids were the major fraction and increased further (49.74 %) in stressed cells, with oleic acid as the most abundant compound (46.97 %). The polyunsaturated fatty acid composition of this algal oil appears to meet the European Standard EN 14214. These results indicate that S. acutus oil meets the requirements for its use as a biodiesel feedstock. Since this strain was also proposed for wastewater bioremediation, this opens up the possibility of its use in an integrated system combined with biofuel production.     

Biomass productivity of two <Emphasis Type="Italic">Scenedesmus</Emphasis> strains cultivated semi-continuously in outdoor raceway ponds and flat-panel photobioreactors

Semi-continuous algal cultivation was completed in outdoor flat-panel photobioreactors (panels) and open raceway ponds (raceways) from February 17 to May 7, 2015 for side-by-side comparison of areal productivities at the Arizona Center for Algae Technology and Innovation in Mesa, AZ, USA. Experiments used two strains of Scenedesmus acutus (strains LB 0414 and LB 0424) to assess productivity, areal density, nutrient removal, and harvest volume across cultivation systems and algal strains. Panels showed an average biomass productivity of 19.0?±?0.6 g m^?2 day^?1 compared to 6.62?±?2.3 g m^?2 day^?1 for raceways. Photosynthetic efficiency ranged between 1.32 and 2.24 % for panels and between 0.30 and 0.68 % for raceways. Panels showed an average nitrogen consumption rate of 38.4?±?8.6 mg N L^?1 day^?1. Cultivation in raceways showed a consumption rate of 3.8?±?2.5 and 7.1?±?4.2 mg N L^?1 day^?1 for February/March and April/May, respectively, due to increase in biomass productivity. Excess nutrients were required to prevent a decrease in productivity. Daily biomass harvest volumes between 18 and 36 % from panels did not affect culture productivity, but density decreased with increased harvest volume. High cultivation temperatures above 30 °C caused strain LB 0414 to lyse and crash. Strain LB 0424 did not show any difference in biomass productivity when peak temperatures reached 34, 38, or 42 °C, but showed decreased productivity when the peak temperature during cultivation was 30 °C. Using algal strains with different temperature tolerances can generate increased annual biomass productivity.     

Genetic manipulation, a feasible tool to enhance unique characteristic of Chlorella vulgaris as a feedstock for biodiesel production

Developing a reliable technique to transform unicellular green algae, Chlorella vulgaris, could boost potentials of using microalgae feedstock in variety of applications such as biodiesel production. Volumetric lipid productivity (VLP) is a suitable variable for evaluating potential of algal species. In the present study, the highest VLP level was recorded for C. vulgaris (79.08 mg l^?1 day^?1) followed by 3 other strains studied; C. emersonii, C. protothecoides, and C. salina by 54.41, 45 and 18.22 mg l^?1day^?1, respectively. Having considered the high productivity of C. vulgaris, it was selected for the preliminary transformation experiment through micro-particle bombardment. Plasmid pBI 121, bearing the reporter gene under the control of CaMV 35S promoter and the kanamycin marker gene, was used in cells bombardment. Primary selection was done on a medium supplemented by 50 mg l^?1 kanamycin. After several passages, the survived cells were PCR-tested to confirm the stability of transformation and then were found to exhibit β-glucuronidase (GUS) activity in comparison with the control cells. Southern hybridization of npt II probe with genomic DNA revealed stable integration of the cassette in three different positions in the genome. The whole process was successfully implemented as a pre-step to transform the algal cells by genes involved in lipid production pathway which will be carried out in our future studies.     

Comparison of growth of Tetraselmis in a tubular photobioreactor (Biocoil) and a raceway pond

Microalgae cultivation systems can be divided broadly into open ponds and closed photobioreactors. This study investigated the growth and biomass productivity of the halophilic green alga Tetraselmis sp. MUR-233, grown outdoors in paddle wheel-driven open raceway ponds and in a tubular closed photobioreactor (Biocoil) at a salinity of 7 % NaCl (w/v) between mid-March and June 2010 (austral autumn/winter). Volumetric productivity in the Biocoil averaged 67 mg ash-free dry weight (AFDW) L^?1 day^?1 when the culture was grown without CO₂ addition. This productivity was 86 % greater, although less stable, than that achieved in the open raceway pond (36 mg L^?1 day^?1) grown at the same time in the autumn period. The Tetraselmis culture in the open raceway pond could be maintained in semi-continuous culture for the whole experimental period of 3 months without an additional CO₂ supply, whereas in the Biocoil, under the same conditions, reliable semi-continuous culture was only achievable for a period of 38 days. However, stable semi-continuous culture was achieved in the Biocoil by the addition of CO₂ at a controlled pH of ~7.5. With CO₂ addition, the volumetric biomass productivity in the Biocoil was 85 mg AFDW L^?1 day^?1 which was 5.5 times higher than the productivity achieved in the open raceway pond (15 mg AFDW L^?1 day^?1) with CO₂ addition and 8 times higher compared to the productivity in the open raceway pond without CO₂ addition (11 mg AFDW L^?1 day^?1), when cultures were grown in winter. The illuminated area productivities highlight an alternative story and showed that the open raceway pond had a three times higher productivity (3,000 mg AFDW m^?2 day^?1) compared to the Biocoil (850 mg AFDW m^?2 day^?1). Although significant differences were found between treatments and cultivation systems, the overall average lipid content for Tetraselmis sp. MUR-233 was 50 % in exponential phase during semi-continuous cultivation.     

Biomass and Lipid Production of Dinoflagellates and Raphidophytes in Indoor and Outdoor Photobioreactors

The principal fatty acids from the lipid profiles of two autochthonous dinoflagellates (Alexandrium minutum and Karlodinium veneficum) and one raphidophyte (Heterosigma akashiwo) maintained in bubble column photobioreactors under outdoor culture conditions are described for the first time. The biomass production, lipid content and lipid productivity of these three species were determined and the results compared to those obtained when the strains were cultured indoors. Under the latter condition, the biotic values did not significantly differ among species, whereas under outdoor conditions, differences in both duplication time and fatty acids content were observed. Specifically, A. minutum had higher biomass productivity (0.35 g·L^?1 day^?1), lipid productivity (80.7 mg lipid·L^?1 day^?1) and lipid concentration (252 mg lipid·L^?1) at harvest time (stationary phase) in outdoor conditions. In all three strains, the growth rate and physiological response to the light and temperature fluctuations of outdoor conditions greatly impacted the production parameters. Nonetheless, the species could be successfully grown in an outdoor photobioreactor and were of sufficient robustness to enable the establishment of long-term cultures yielding consistent biomass and lipid production.     

Long-term outdoor growth and lipid productivity of Tetraselmis suecica, Dunaliella tertiolecta and Chlorella sp (Chlorophyta) in bag photobioreactors

There has been considerable interest on cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. The ideal microalga characteristics are that it must grow well even under high cell density and under varying outdoor environmental conditions and be able to have a high biomass productivity and contain a high oil content (~25–30 %). The main advantage of Chlorophyta is that their fatty acid profile is suitable for biodiesel conversion. Tetraselmis suecica CS-187 and Chlorella sp. were grown semi-continuously in bag photobioreactors (120 L, W?×?L?=?40?×?380 cm) over a period of 11 months in Melbourne, Victoria, Australia. Monthly biomass productivity of T. suecica CS-187 and Chlorella sp. was strongly correlated to available solar irradiance. The total dry weight productivity of T. suecica and Chlorella sp. was 110 and 140 mg L^?1 d^?1, respectively, with minimum 25 % lipid content for both strains. Both strains were able to tolerate a wide range of shear produced by mixing. Operating cultures at lower cell density resulted in increasing specific growth rates of T. suecica and Chlorella sp. but did not affect their overall biomass productivity. On the other hand, self shading sets the upper limit of operational maximum cell density. Several attempts in cultivating Dunaliella tertiolecta CS-175 under the same climatic conditions were unsuccessful.     

Lipid productivity and fatty acid composition-guided selection of Chlorella strains isolated from Malaysia for biodiesel production

The need to develop biomass-based domestic production of high-energy liquid fuels (biodiesel) for transportation can potentially be addressed by exploring microalgae with high lipid content. Selecting the strains with adequate oil yield and quality is of fundamental importance for a cost-efficient biofuel feedstock production based on microalgae. This work evaluated 29 strains of Chlorella isolated from Malaysia as feedstock for biodiesel based on volumetric lipid productivity and fatty acid profiles. Phylogenetic studies based on 18S rRNA gene revealed that majority of the strains belong to true Chlorella followed by Parachlorella. The strains were similarly separated into two groups based on fatty acid composition. Of the 18 true Chlorella strains, Chlorella UMACC187 had the highest palmitic acid (C16:0) content (71.3?±?4.2 % total fatty acids, TFA) followed by UMACC84 (70.1?±?0.7 %TFA), UMACC283 (63.8?±?0.7 %TFA), and UMACC001 (60.3?±?4.0 %TFA). Lipid productivity of the strains at exponential phase ranged from 34.53 to 230.38 mg L^?1 day^?1, with Chlorella UMACC050 attaining the highest lipid productivity. This study demonstrated that Chlorella UMACC050 is a promising candidate for biodiesel feedstock production.     

Optimization of CO2 concentration and light intensity for biodiesel production by Chlorella vulgaris FACHB-1072 under nitrogen deficiency with phosphorus luxury uptake

Microalgal biodiesel is an alternative bioenergy for the future. Nitrogen deprivation is usually used to increase lipid content in microalgae, however, it also lowers biomass production, resulting in not much increase of lipid productivity. Our previous study found that phosphorus played an important role in enhancing biodiesel productivity of C. vulgaris FACHB-1072 under nitrogen deficient condition. The aim of this study was to optimize two significant parameters of CO₂ concentration (0.03, 4, 6, 12 %) and light intensity (40, 120, 200 μmol photons m^-2 s^-1) with respect to biodiesel productivity and P uptake rate of C. vulgaris FACHB-1072. It was found that the optimized conditions were 4 % CO₂ concentration and 200 μmol photons m^-2 s^-1 light intensity. The maximum biodiesel productivity was 34.56 mg L^-1 day^-1; 2.7 times higher than the control (nutrient sufficient condition). Phosphorus was accumulated as polyphosphate and its maximum uptake rate was 2.08 mg L^-1 day^-1; twice that of the control. After optimization, the performances under nitrogen deficiency were significantly better compared with those under nitrogen sufficiency, which were rarely reported in literature. Our findings suggest a great potential to combine phosphorus removal from wastewater with biodiesel production via microalgae.     

Optimization of aeration for biodiesel production by <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> grown in municipal wastewater

Despite the significant breakthroughs in research on microalgae as a feedstock for biodiesel, its production cost is still much higher than that of fossil diesel. One possible solution to overcome this problem is to optimize algal growth and lipid production in wastewater. The present study examines the optimization of pretreatment of municipal wastewater and aeration conditions in order to enhance the lipid productivity of Scenedesmus obliquus. Results showed that no significant differences were recorded in lipid productivity of S. obliquus grown in primary settled or sterilized municipal wastewater; however, ultrasound pretreatment of wastewater significantly decreased the lipid production. Whereas, aeration rates of 0.2 vvm significantly increased lipid content by 51 %, with respect to the non-aerated culture, which resulted in maximum lipid productivity (32.5 mg L^?1 day^?1). Furthermore, aeration enrichment by 2 % CO₂ resulted in increase of lipid productivity by 46 % over the CO₂ non-enriched aerated culture. Fatty acid profile showed that optimized aeration significantly enhanced monounsaturated fatty acid production, composed mainly of C18:1, by 1.8 times over the non-aerated S. obliquus culture with insignificant changes in polyunsaturated fatty acid proportion; suggesting better biodiesel characteristics for the optimized culture.     

Biomass and terpenoids produced by mutant strains of <Emphasis Type="Italic">Arthrospira</Emphasis> under low temperature and light conditions

The filamentous Cyanobacterium Arthrospira is commercially produced and is a functional, high-value, health food. We identified 5 low temperature and low light intensity tolerant strains of Arthrospira sp. (GMPA1, GMPA7, GMPB1, GMPC1, and GMPC3) using ethyl methanesulfonate mutagenesis and low temperature screening. The 5 Arthrospira strains grew rapidly below 14?°C, 43.75 μmol photons m^?2 s^?1 and performed breed conservation at 2.5?°C, 8.75 μmol photons m^?2 s^?1. We used morphological identification and molecular genetic analysis to identify GMPA1, GMPA7, GMPB1 and GMPC1 as Arthrospira platensis, while GMPC3 was identified as Arthrospira maxima. Growth at different culture temperatures was determined at regular intervals using dry biomass. At 16?°C and 43.75 μmol photons m^?2 s^?1, the maximum dry biomass production and the mean dry biomass productivity of GMPA1, GMPB1, and GMPC1 were 2057?±?80 mg l^?1, 68.7?±?2.5 mg l^?1 day^?1, 1839?±?44 mg l^?1, 60.6?±?1.8 mg l^?1 day^?1, and 2113?±?64 mg l^?1, 77.7?±?2.5 mg l^?1 day^?1 respectively. GMPB1 was chosen for additional low temperature tolerance studies and growth temperature preference. In winter, GMPB1 grew well at mean temperatures <10?°C, achieving 3258 mg dry biomass from a starting 68 mg. In summer, GMPB1 grew rapidly at mean temperatures more than 28?°C, achieving 1140 mg l^?1 dry biomass from a starting 240 mg. Phytonutrient analysis of GMPB1 showed high levels of C-phycocyanin and carotenoids. Arthrospira metabolism relates to terpenoids, and the methyl-d-erythritol 4-phosphate pathway is the only terpenoid biosynthetic pathway in Cyanobacteria. The 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) gene from GMPB1 was cloned and phylogenetic analysis showed that GMPB1 is closest to the Cyanobacterium Oscillatoria nigro-viridis PCC711. Low temperature tolerant Arthrospira strains could broaden the areas suitable for cultivation, extend the seasonal cultivation time, and lower production costs.     

24-Epibrassinolide alleviates salt-induced inhibition of productivity by increasing nutrients and compatible solutes accumulation and enhancing antioxidant system in wheat (Triticum aestivum L.)

Two wheat (Triticum aestivum L.) cultivars, Sids 1 and Giza 168, were grown under non-saline or saline conditions (4.7 and 9.4 dS m^?1) and were sprayed with 0.00, 0.05 and 0.10 mg l^?1 24-epibrassinolide (EBL). Salt stress markedly decreased plant productivity and N, P, and K uptake, particularly in Giza 168. A follow-up treatment with 0.1 mg l^?1 EBL detoxified the stress generated by salinity and considerably improved the above parameters, especially in Sids 1. Organic solutes (soluble sugars, free amino acids, proline and glycinebetaine), antioxidative enzymes (superoxide dismutase, peroxidase, catalase and glutathione reductase), antioxidant molecules (glutathione and ascorbate) and Ca and Mg levels were increased under saline condition, and these increases proved to be more significant in salt-stressed plants sprayed with EBL, particularly at 0.1 mg l^?1 EBL with Sids 1. Sodium concentration, lipid peroxidation, hydrogen peroxide content and electrolyte leakage were increased under salt stress and significantly decreased when 0.1 mg l^?1 EBL was sprayed. Clearly, EBL alleviates salt-induced inhibition of productivity by altering the physiological and biochemical properties of the plant.     

Process Engineering for High-Cell-Density Cultivation of Lipid Rich Microalgal Biomass of <Emphasis Type="Italic">Chlorella</Emphasis> sp. FC2 IITG

In the present study, process engineering strategy was applied to achieve lipid-rich biomass with high density of Chlorella sp. FC2 IITG under photoautotrophic condition. The strategy involved medium optimization, intermittent feeding of limiting nutrients, dynamic change in light intensity, and decoupling growth and lipid induction phases. Medium optimization was performed using combinations of artificial neural network or response surface methodology with genetic algorithm (ANN-GA and RSM-GA). Further, a fed-batch operation was employed to achieve high cell density with intermittent feeding of nitrate and phosphate along with stepwise increase in light intensity. Finally, mutually exclusive biomass and lipid production phases were decoupled into two-stage cultivation process: biomass generation in first stage under nutrient sufficient condition followed by lipid enrichment through nitrogen starvation. The key findings were as follows: (i) ANN-GA resulted in an increase in biomass titer of 157 % (0.95 g L^?1) in shake flask and 42.8 % (1.0 g L^?1) in bioreactor against unoptimized medium at light intensity of 20 μE m^?2 s^?1; (ii) further optimization of light intensity in bioreactor gave significantly improved biomass titer of 5.6 g L^?1 at light intensity of 250 μE m^?2 s^?1; (iii) high cell density of 13.5 g L^?1 with biomass productivity of 675 mg L^?1 day^?1 was achieved with dynamic increase in light intensity and intermittent feeding of limiting nutrients; (iv) finally, two-phase cultivation resulted in biomass titer of 17.7 g L^?1 and total lipid productivity of 313 mg L^?1 day^?1 which was highest among Chlorella sp. under photoautotrophic condition.     

Ammonium,nitrate, and urea play different roles for lipid accumulation in the nervonic acid—producing microalgae <Emphasis Type="Italic">Mychonastes afer</Emphasis> HSO-3-1

Producing valuable coproducts from oleaginous microalgae is an option to reduce the total cost of biofuel production. Here, the influence of nitrogen sources on biomass yield and lipid accumulation of a newly identified oleaginous green microalgal strain, Mychonastes afer HSO-3-1, was evaluated. Carbon assimilation and the following lipid biosynthesis of M. afer were inhibited to some extent under weak acidic conditions (6 < pH < 7) and any of the tested nitrogen source. The highest lipid productivity of 50.7 mg L^?1 day^?1 was achieved with a 17.6 mM nitrogen supplement in the form of urea. The cell polar lipid content was significantly higher than triacylglycerol (TAG), and saturated palmitic acid (C16:0) occupied a dominant position in the fatty acid profiles while culturing M. afer in acidic medium with NH₄ ⁺ as the nitrogen source. Under neutral conditions, the lipid productivities of M. afer cultivated in media containing 17.6 mM of NaNO₃, NH₄Cl, and NH₄NO₃ were 76.2, 77.5, and 79.0 mg L^?1 day^?1, respectively. The greatest TAG content (58.56%) of total lipids was obtained when NaNO₃ was used as the nitrogen source. There was no significant difference in the fatty acid composition of M. afer cells when they were cultivated in neutral media supplemented with NaNO₃, urea, NH₄Cl, and NH₄NO₃. Therefore, NH₄ ⁺ was not a suitable nitrogen source for M. afer cultivation due to the additional labor, working procedures, and alkali required to adjust the medium pH. Considering that using urea as nitrogen source could reduce the cost of nutrient salts substantially and urea can be taken up and utilized by most microalgae, it is a preferred nitrogen source. The major properties of biodiesel derived from M. afer HSO-3-1 met biodiesel quality, and nervonic acid concentrations remained at approximately 3.0% of total fatty acids.     

The effect of nitrogen limitation on lipid productivity and cell composition in Chlorella vulgaris

Chlorella vulgaris accumulates lipid under nitrogen limitation, but at the expense of biomass productivity. Due to this tradeoff, improved lipid productivity may be compromised, despite higher lipid content. To determine the optimal degree of nitrogen limitation for lipid productivity, batch cultures of C. vulgaris were grown at different nitrate concentrations. The growth rate, lipid content, lipid productivity and biochemical and elemental composition of the cultures were monitored for 20 days. A starting nitrate concentration of 170 mg L^?1 provided the optimal tradeoff between biomass and lipid production under the experimental conditions. Volumetric lipid yield (in milligram lipid per liter algal culture) was more than double that under nitrogen-replete conditions. Interpolation of the data indicated that the highest volumetric lipid concentration and lipid productivity would occur at nitrate concentrations of 305 and 241 mg L^?1, respectively. There was a strong correlation between the nitrogen content of the cells and the pigment, protein and lipid content, as well as biomass and lipid productivity. Knowledge of the relationships between cell nitrogen content, growth, and cell composition assists in the prediction of the nitrogen regime required for optimal productivity in batch or continuous culture. In addition to enhancing lipid productivity, nitrogen limitation improves the lipid profile for biodiesel production and reduces the requirement for nitrogen fertilizers, resulting in cost and energy savings and a reduction in the environmental burden of the process.     

Mixture design as a potential tool in modeling the effect of light wavelength on Dunaliella salina cultivation: an alternative solution to increase microalgae lipid productivity for biodiesel production

Abstract

For a feasible microalgae biodiesel, increasing lipid productivity is a key parameter. An important cultivation parameter is light wavelength (λ). It can affect microalgal growth, lipid yield, and fatty acid composition. In the current study, the mixture design was used as an alternative to model the influence of the λ on the Dunaliella salina lipid productivity. The illumination was considered to be the mixture of different λ (the light colors blue, red, and green). All experiments were performed with and without sodium acetate (4?g/L), as carbon source, allowing the identification of the impact of the cultivation regimen (autotrophic or mixotrophic). Without sodium acetate, the highest lipid productivity was obtained using blue and red light. The use of mixotrophic cultivations significantly enhanced the results. The optimum obtained result was mixotrophic cultivation under 65% blue and 35% green light, resulting in biomass productivity of 105.06 mgL^?1day^?1, a lipid productivity of 53.47 mgL^?1day^?1, and lipid content of 50.89%. The main fatty acids of the oil obtained in this cultivation were oleic acid (36.52%) and palmitic acid (18.31%).