Optimization of cultivation conditions for fatty acid composition and EPA production in the eustigmatophycean microalga Trachydiscus minutus

We determined the effects of cultivation conditions (nitrogen source, salinity, light intensity, temperature) on the composition of polyunsaturated fatty acids (PUFAs) and the production of eicosapentaenoic acid (EPA) in the laboratory cultured eustigmatophycean microalga, Trachydiscus minutus. T. minutus was capable of utilizing all nitrogen compounds tested (potassium nitrate, urea, ammonium nitrate, ammonium carbonate) with no differences in growth and only minor differences in fatty acid (FA) compositions. Ammonium carbonate was the least appropriate for lipid content and EPA production, while urea was as suitable as nitrates. Salinity (0.2 % NaCl) slightly stimulated EPA content and inhibited growth. Increasing salinity had a marked inhibitory effect on growth and PUFA composition; salinity at or above 0.8 % NaCl was lethal. Both light intensity and temperature had a distinct effect on growth and FA composition. The microalga grew best at light intensities of 470–1,070 μmol photons m^?2 s^?1 compared to 100 μmol photons m^?2 s^?1, and at 28 °C; sub-optimal temperatures (20, 33 °C) strongly inhibited growth. Saturated fatty acids increased with light intensity and temperature, whereas the reverse trend was found for PUFAs. Although the highest level of EPA (as a proportion of total FAs) was achieved at a light intensity of 100 μmol photons m^?2 s^?1 (51.1?± 2.8 %) and a temperature of 20 °C (50.9?±?0.8 %), the highest EPA productivity of about 30 mg L^?1?day^?1 was found in microalgae grown at higher light intensities, at 28 °C. Overall, for overproduction of EPA in microalgae, we propose that outdoor cultivation be used under conditions of a temperate climatic zone in summer, using urea as a nitrogen source.     

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.     

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.     

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.     

Potential Outdoor Cultivation of Green Microalgae Based on Response to Changing Temperatures and by Combining with Air Temperature Occurrence

In this study, our working hypothesis was to examine whether temperature alters biomass and metabolite production by microalgae according to strain. We also addressed whether it is possible to choose a strain suitable for growing in each season of a given region. A factorial experiment revealed a significant interaction between chlorophylls a and b (Chl a and Chl b), carotenoid/Chl (a?+?b) ratio, biomass and total lipid productivity of six green microalgae (four Chlorella spp., Chlorella sorokiniana and Neochloris oleoabundans) after 15 days at four temperatures. At 39/35 °C, two Chlorella sp. strains (IPR7115 and IPR7117) showed higher total carotenoids/Chl (a?+?b) (0.578 and 0.830), respectively. N. oleoabundans had the highest Chl a (8210 μg L^?1) and Chl b (1909 μg L^?1) at 19/15 °C and highest maximum dry biomass (2900 mg L^?1), specific growth rate (0.538 day^?1) and total lipids (1003 mg L^?1) at 15/8 °C. We applied a method to infer the growth of these six green microalgae in outdoor ponds, as based on their response to changing temperatures and by combining with historical data on day/night air temperature occurrence for a given region. We conclude that the use of regionalized maps based on air temperature is a good strategy for predicting microalgal cultivation in outdoor ponds based on their features and tolerance to changing temperature.     

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.     

Growth and palmitoleic acid accumulation of filamentous oleaginous microalgae <Emphasis Type="Italic">Tribonema minus</Emphasis> at varying temperatures and light regimes

Palmitoleic acid (C16:1Δ9), contributes greatly to human health, industrial chemicals and biodiesel. The filamentous oleaginous microalgae Tribonema sp. has been identified as a highly efficient producer of palmitoleic acid. Temperature and light regime were adapted to regulate the palmitoleic acid content in this study. Strain T. minus was able to grow well at all the tested temperatures, even at 5 °C. The optimum temperature for palmitoleic acid accumulation (54.25 % of total fatty acid) was 25 °C. Moreover, both light intensity and photoperiod affect the growth, lipid content and fatty acid files of T. minus. The culture exposed to 240 μmol photons m^?2 s^?1 with a photoperiod of 24:0 showed the highest biomass (6.87 g L^?1) and biggest lipid content (61.27 % of dry weight), whereas the most amount of palmitoleic acid (50.47 % of total fatty acid) was detected at 120 μmol photons m^?2 s^?1. These findings make tangible contributions to culture T. minus for commercial production of lipid or palmitoleic acid.     

Effects of Initial Phosphorus Concentration and Light Intensity on Biomass Yield per Phosphorus and Lipid Accumulation of Scenedesmus sp. LX1

Phosphorus has been considered as one of the most important limiting resources of large-scale production of microalgal biofuel. The approaches to increase biomass yield per phosphorus, along with the lipid accumulation properties of Scenedesmus sp. LX1, were investigated in this study. It was found that practical biomass yield per phosphorous was reduced with the increase of initial phosphorus (P) concentration, but increased with light intensity. The highest biomass yield per P of 4,500 kg-biomass/kg-P was achieved at initial phosphorus concentration of 0.05 mg?·?L^?1 under the light intensity of 320 μmol photon?·?m^?2?·?s^?1. Furthermore, the lipid content per biomass and triacylglycerols (TAGs) content per lipid were found to be positively correlated to biomass yield per P. With the biomass yield increased from 2,800 kg-biomass/kg-P to 4,500 kg-biomass/kg-P, the lipid content per microalgal biomass and TAG content per lipid increased from 18.7 % to 35.0 % and from 69.5 % to 83.0 %. These results suggested a possible approach to achieve high biomass production and high lipid content simultaneously.     

Growth and lipid synthesis promotion in mixotrophic Neochloris oleoabundans (Chlorophyta) cultivated with glucose

In the recent years, the studies concerning the cultivation of Neochloris oleoabundans for biofuel purposes have increased, in relation to its capability to accumulate lipids when grown under nutrient starvation. Unfortunately, this cultivation mode does not allow to reach high biomass densities, which are required to improve the feasibility of the process. Increasing knowledge of the microalgal physiology is necessary to obtain new useful information for the improvement of culture performance in the perspective of large-scale cultivation. In this work, the mixotrophic cultivation of N. oleoabundans in a brackish medium added with different glucose concentrations has been tested under shaking, with the aim of stimulating growth alongside lipid accumulation inside cells. Cell morphology, glucose consumption, photosynthetic pigment content and photosynthetic efficiency were also investigated. Among all tested glucose concentrations (0–30 g L^?1), it was observed that 2.5 g L^?1 was the optimal concentration, allowing to obtain the best compromise between glucose supplement, biomass production and lipid accumulation. Growth was highly enhanced in mixotrophic cultures, linked to the release of cells from sporocysts. A unique feature characterising mixotrophy in N. oleoabundans was the promotion of the maximum quantum yield of Photosystem II. Moreover, when mixotrophic cells entered the stationary phase, high lipid accumulation was induced. This study shows that the addition of glucose to N. oleoabundans remarkably increases the production of biomass enriched in lipids and represents an advancement for the cultivation of this microalga for applied purposes.     

Statistical evaluation and modeling of cheap substrate-based cultivation medium of Chlorella vulgaris to enhance microalgae lipid as new potential feedstock for biolubricant

Chlorella vulgaris (C. vulgaris) microalga was investigated as a new potential feedstock for the production of biodegradable lubricant. In order to enhance microalgae lipid for biolubricant production, mixotrophic growth of C. vulgaris was optimized using statistical analysis of Plackett–Burman (P-B) and response surface methodology (RSM). A cheap substrate-based medium of molasses and corn steep liquor (CSL) was used instead of expensive mineral salts to reduce the total cost of microalgae production. The effects of molasses and CSL concentration (cheap substrates) and light intensity on the growth of microalgae and their lipid content were analyzed and modeled. Designed models by RSM showed good compatibility with a 95% confidence level when compared to the cultivation system. According to the models, optimal cultivation conditions were obtained with biomass productivity of 0.123 g L^?1 day^?1 and lipid dry weight of 0.64 g L^?1 as 35% of dry weight of C. vulgaris. The extracted microalgae lipid presented useful fatty acid for biolubricant production with viscosities of 42.00 cSt at 40°C and 8.500 cSt at 100°C, viscosity index of 185, flash point of 185°C, and pour point of ?6°C. These properties showed that microalgae lipid could be used as potential feedstock for biolubricant production.     

Biomass and Total Lipid Content Assessment of Microalgal Cultures Using Near and Short Wave Infrared Spectroscopy

The technique of near and short wave near-infrared spectroscopy was assessed with respect to analysis of dry matter and lipid content of microalgae with potential for biodiesel production. Microalgal culture samples were filtered through GF/C filter papers and spectral measurements of wet and oven dried (60 °C overnight) filter papers over the ranges of 300–1,100 nm and 1,100–2,500 nm were recorded. Partial least square models on culture biomass and lipid content for combined species data were poor in terms of RMSECV, R _CV and the ratio of RMSECV to SD. A single species model for C. vulgaris based on 1,100–2,500 nm spectra of dry filtrate supported a model with RMSECV, R _CV and SDR values of 0.32 g L^?1, 0.955 and 3.38 for biomass and 0.089 g L^?1, 0.874 and 2.06 with lipid, respectively. However, the dry filtrate models on biomass and lipid content performed poorly in the prediction of samples drawn from an independent series of C. vulgaris cultured under N-, P- and Fe-limited growth trial. Thus, while the near-infrared spectroscopy technique has potential for assessment of dry matter and lipid content of microalgal cultures using a dried filtrate sample, further work is required to examine the limits to model robustness.     

Irradiance optimization of outdoor microalgal cultures using solar tracked photobioreactors

Photosynthetic activity and temperature regulation of microalgal cultures (Chlorella vulgaris and Scenedesmus obliquus) under different irradiances controlled by a solar tracker and different cell densities were studied in outdoor flat panel photobioreactors. An automated process control unit regulated light and temperature as well as pH value and nutrient concentration in the culture medium. CO₂ was supplied using flue gas from an attached combined block heat and power station. Photosynthetic activity was determined by pulse amplitude modulation fluorometry. Compared to the horizontal irradiance of 55 mol photons m^?2 d^?1 on a clear day, the solar tracked photobioreactors enabled a decrease and increase in the overall light absorption from 19 mol photons m^?2 d^?1 (by rotation out of direct irradiance) to 79 mol photons m^?2 d^?1 (following the position of the sun). At biomass concentrations below 1.1 g cell dry weight (CDW) L^?1, photoinhibition of about 35 % occurred at irradiances of ≥1,000 μmol photons m^?2 s^?1 photosynthetic active radiation (PAR). Using solar tracked photobioreactors, photoinhibition can be reduced and at optimum biomass concentration (≥2.3 g CDW L^?1), the culture was irradiated up to 2,000 μmol photons m^?2 s^?1 to overcome light limitation with biomass yields of 0.7 g CDW mol photons^?1 and high photosynthetic activities indicated by an effective quantum yield of 0.68 and a maximum quantum yield of 0.80 (F _v/F _m). Overheating due to high irradiance was avoided by turning the PBR out of the sun or using a cooling system, which maintained the temperature close to the species-specific temperature optima.     

Effects of stationary phase elongation and initial nitrogen and phosphorus concentrations on the growth and lipid-producing potential of Chlorella sp. HQ

Higher lipid production and nutrient removal rates are the pursuing goals for synchronous biodiesel production and wastewater treatment technology. An oleaginous alga Chlorella sp. HQ was tested in five different synthetic water, and it was found to achieve the maximum biomass (0.27 g L^?1) and lipid yield (41.3 mg L^?1) in the synthetic secondary effluent. Next, the effects of the stationary phase elongation and initial nitrogen (N) and phosphorus (P) concentrations were investigated. The results show that the algal characteristics were affected apparently under different N concentrations but not P, which were verified by Logistic and Monod models. At the early stationary phase, the algal biomass, lipid and triacylglycerols (TAGs) yields, and P removal efficiency increased and reached up to 0.19 g L^?1, 46.7 mg L^?1, 14.3 mg L^?1, and 94.3 %, respectively, but N removal efficiency decreased from 86.2 to 26.8 % under different N concentrations. And the largest TAGs yield was only 6.4 mg L^?1 and N removal efficiency was above 71.1 % under different P concentrations. At the late stationary phase, the maximal biomass, lipid and TAGs yields, and P removal efficiencies primarily increased as the initial N and P concentrations increase and climbed up to 0.49 g L^?1, 99.2 mg L^?1, 54.0 mg L^?1, and 100.0 %, respectively. It is concluded that stationary phase elongation is of great importance and the optimal initial N/P ratio should be controlled between 8/1 and 20/1 to serve Chlorella sp. HQ for better biodiesel production and secondary effluent purification.     

Effect of nitrate on lipid production by T. suecica, M. contortum, and C. minutissima

Microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Nitrate is a good nitrogen source for many microalgae and affects biomass and lipid yields of microalgae. In this study, the effect of nitrate on cell growth and lipid production and composition in Monoraphidium contortum, Tetraselmis suecica, and Chlorella minutissima was investigated. Nitrate affected the production of biomass and the production and composition of lipids of the three microalgae tested. Increasing the nitrate concentration in the culture medium resulted in increased biomass production and higher biomass productivity. Furthermore, increasing the nitrate concentration resulted in a reduction in lipid content and productivity in M. contortum; however, the opposite effect was observed in T. suecica and C. minutissima cultures. C. minutissima and M. contortum lipids contain high levels of oleic acid, with values ranging from 26 to 45.7% and 36.4 to 40.1%, respectively. The data suggest that because of its high lipid productivity (13.79 mg L^?1 d^?1) and high oleic acid productivity (3.78 mg L^?1 d^?1), Chlorella minutissima is a potential candidate for the production of high quality biodiesel.     

Responses of a new isolated <Emphasis Type="Italic">Cyanobacterium aponinum</Emphasis> strain to temperature,pH, CO<Subscript>2</Subscript> and light quality

A new strain of cyanobacteria was isolated from seawater samples collected near Jimo hot springs, Qingdao, China, and was identified as Cyanobacterium aponinum by 16S rDNA analysis. This study examined the effects of temperature, pH, light quality and high CO₂ concentration on the growth of the cyanobacteria. Results showed that the strain exhibited a higher growth rate (about 168.4 mg L^?1 day^?1) at 35 °C than other temperatures (surviving at up to 50 °C) and a wide growth tolerance to acidic stress (pH 3.0 to 4.0) resulting from either H₂SO₄ or HNO₃. The four light qualities, ranked by greatest to least biomass effect, were as follows: LED white light (LW) > LED red light (LR) > fluorescent white light (FW) > LED blue light (LB), achieving a higher lighting effect at a LW light intensity (60 μmol photons m^?2 s^?1) lower than other light qualities, which implied less energy consumption therewith. This strain demonstrates excellent CO₂ tolerance at least 10% CO₂ with the highest productivity in biomass (about 337.8 mg L^?1 day^?1) measured at 1% CO₂ level. Results indicate that this strain is a promising candidate for use in biofixation of CO₂ from flue gases emitted by thermoelectric plants.     

Inorganic carbon and pH effect on growth and lipid productivity of Tetraselmis suecica and Chlorella sp (Chlorophyta) grown outdoors in bag photobioreactors

There has been considerable interest in cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. However, almost all mass cultures of algae are carbon-limited. Therefore, to reach a high biomass and oil productivities, the ideal selected microalgae will most likely need a source of inorganic carbon. Here, growth and lipid productivities of Tetraselmis suecica CS-187 and Chlorella sp were tested under various ranges of pH and different sources of inorganic carbon (untreated flue gas from coal-fired power plant, pure industrial CO₂, pH-adjusted using HCl and sodium bicarbonate). Biomass and lipid productivities were highest at pH 7.5 (320?±?29.9 mg biomass L^?1 day^?1and 92?±?13.1 mg lipid L^?1 day^?1) and pH 7 (407?±?5.5 mg biomass L^?1 day^?1 and 99?±?17.2 mg lipid L^?1 day^?1) for T. suecica CS-187 and Chlorella sp, respectively. In general, biomass and lipid productivities were pH 7.5?>?pH 7?>?pH 8?>?pH 6.5 and pH 7?>?pH 7.5?=?pH 8?>?pH 6.5?>?pH 6?>?pH 5.5 for T. suecica CS-187 and Chlorella sp, respectively. The effect of various inorganic carbon on growth and productivities of T. suecica (regulated at pH?=?7.5) and Chlorella sp (regulated at pH?=?7) grown in bag photobioreactors was also examined outdoor at the International Power Hazelwood, Gippsland, Victoria, Australia. The highest biomass and lipid productivities of T. suecica (51.45?±?2.67 mg biomass L^?1 day^?1 and 14.8?±?2.46 mg lipid L^?1 day^?1) and Chlorella sp (60.00?±?2.4 mg biomass L^?1 day^?1 and 13.70?±?1.35 mg lipid L^?1 day^?1) were achieved when grown using CO₂ as inorganic carbon source. No significant differences were found between CO₂ and flue gas biomass and lipid productivities. While grown using CO₂ and flue gas, biomass productivities were 10, 13 and 18 %, and 7, 14 and 19 % higher than NaHCO₃, HCl and unregulated pH for T. suecica and Chlorella sp, respectively. Addition of inorganic carbon increased specific growth rate and lipid content but reduced biomass yield and cell weight of T. suecica. Addition of inorganic carbon increased yield but did not change specific growth rate, cell weight or content of the cell weight of Chlorella sp. Both strains showed significantly higher maximum quantum yield (F_v/F_m) when grown under optimum pH.     

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.     

Biomass,Lipid and Fatty Acid Production in Large-Scale Cultures of the Marine Macroalga Derbesia tenuissima (Chlorophyta)

Biomass productivity was quantified for the marine macroalga Derbesia tenuissima cultivated outdoors at seven stocking densities from 0.25 to 8 g L^?1 for 5 weeks. Total lipids and fatty acid quantity and quality was measured from samples that were freeze-dried, dried by oven (75 °C), food dehydrator (60 °C), or outdoor in the sun (40 °C) or shade (38 °C). Stocking densities of 0.25 to 2 g L^?1 yielded the highest biomass productivities (>20 g dry weight m^?2 day^?1) with no effect on total lipid quantity (11 %), or fatty acid quantity (5.3 %) or quality at any density tested. However, there was an interactive effect of stocking density and drying technique, with a decrease of up to 40 % in polyunsaturated fatty acids in sun-dried compared to freeze-dried biomass. Notably, while fatty acid and biomass productivity may be inseparable in macroalgae, cultivation conditions have a significant carryover effect in the post-harvest delivery of high-quality bio-oils.     

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.     

Scenedesmus sp. NJ-1 isolated from Antarctica: a suitable renewable lipid source for biodiesel production

Microalgal lipids are promising alternative feedstocks for biodiesel production. Scenedesmus sp. NJ-1, an oil-rich freshwater microalga isolated from Antarctica, was identified to be a suitable candidate to produce biodiesel in this study. This strain could grow at temperatures ranging from 4 to 35?°C. With regular decrease in nitrate concentration in the medium, large quantities of triacylglycerols accumulated under batch culture conditions detected by thin layer chromatography and BODIPY 505/515 fluorescent staining. Scenedesmus sp. NJ-1 achieved the average biomass productivity of 0.105?g?l^?1?d^?1 (dry weight) and nearly the highest lipid content (35?% of dry cell weight) was reached at day 28 in the batch culture. Neutral lipids accounted for 78?% of total lipids, and C18:1 (n-9), C16:0 were the major fatty acids in total lipids, composing 37 and 20?% of total fatty acids of Scenedesmus sp. NJ-1 grown for 36?days, respectively. These results suggested that Scenedesmus sp. NJ-1 was a good source of microalgal oils for biodiesel production.