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 lipid enhancement in Ankistrodesmus sp. cultured with reused and minimal nutrients media

Microalgae are a promising feedstock for biofuel production. Lipid content in microalgae could be enhanced under nutrient depletion. This work investigated the effect of the nutrient on lipid accumulation in Ankistrodesmus sp. culture. Batch cultures were carried out using fresh BG11 medium, and after the harvest, the medium was reused for the next culture; this method was repeated two times. The maximum lipid productivity of 29.75 mg L^?1 day^?1 was obtained from the culture with the second reuse medium. In continuous cultures, Ankistrodesmus sp. was cultured in both fresh and modified BG11 mediums. The modified BG11 medium was adjusted to resemble the content of the first reuse medium. As a comparison between batch and continuous cultures, it was proven that the productivity in the continuous culture was better than in the batch, where the achievable maximum biomass and lipid were 188.30 and 38.32 mg L^?1 day^?1. The maximum lipid content of 34.22% was obtained from the continuous culture at a dilution rate of 0.08 day^?1, whereas the maximum saturated and unsaturated fatty acid productivities of 79.96 and 104.54 mg L^?1 day^?1 were obtained at a dilution rate of 0.16 day^?1.     

Heterotrophic production of Chlorella sp. TISTR 8990—biomass growth and composition under various production conditions

The green microalga Chlorella sp. TISTR 8990 was grown heterotrophically in the dark using various concentrations of a basal glucose medium with a carbon‐to‐nitrogen mass ratio of 29:1. The final biomass concentration and the rate of growth were highest in the fivefold concentrated basal glucose medium (25 g L^?1 glucose, 2.5 g L^?1 KNO₃) in batch operations. Improving oxygen transfer in the culture by increasing the agitation rate and decreasing the culture volume in 500‐mL shake flasks improved growth and glucose utilization. A maximum biomass concentration of nearly 12 g L^?1 was obtained within 4 days at 300 rpm, 30°C, with a glucose utilization of nearly 76% in batch culture. The total fatty acid (TFA) content of the biomass and the TFA productivity were 102 mg g^?1 and 305 mg L^?1 day^?1, respectively. A repeated fed‐batch culture with four cycles of feeding with the fivefold concentrated medium in a 3‐L bioreactor was evaluated for biomass production. The total culture period was 11 days. A maximum biomass concentration of nearly 26 g L^?1 was obtained with a TFA productivity of 223 mg L^?1 day^?1. The final biomass contained (w/w) 13.5% lipids, 20.8% protein and 17.2% starch. Of the fatty acids produced, 52% (w/w) were saturated, 41% were monounsaturated and 7% were polyunsaturated (PUFA). A low content of PUFA in TFA feedstock is required for producing high quality biodiesel. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1589–1600, 2017     

Attached culture of Nannochloropsis oculata for lipid production

The influences of urea, nitrate and glycine with four concentration levels on attached culture of Nannochloropsis oculata were investigated. The organic nitrogen source glycine was effective on improving not only adhesion biomass productivity but also adhesion rate. The maximum adhesion biomass productivity of 15.76 ± 0.52 g m^?2 day^?1 with adhesion rate of 76.67 ± 0.42 % was achieved with 18 mM glycine. To increase the lipid production, three lipid enhancing strategies were conducted afterwards, including nitrogen starvation, high light, and the combination of nitrogen starvation and high light. In nitrogen starvation situation, although the lipid content was greatly increased, the adhesion biomass productivity dropped probably due to the low cell viability. Increasing light intensity was effective on enhancing both adhesion biomass productivity and lipid content. The results indicated that nitrogen starvation was effective on improving both lipid content and adhesion rate when high light was applied. The maximum lipid yield of 4.32 ± 0.14 g m^?2 day^?1 with adhesion biomass productivity of 21.32 ± 0.65 g m^?2 day^?1, adhesion rate of 86.81 ± 0.10 % and lipid content of 20.24 ± 0.06 % was achieved with the combination strategy.     

Biomass production and fatty acid accumulation in Chlorella sp. (strain DEC1B) isolated from a petrol refinery in Huelva (Spain)

A microalgal strain was established from Cepsa's refinery wastewater treatment plant in Huelva (southwest of Spain). Genetic analysis of the chloroplastic rbcL gene encoding for the large subunit of the ribulose bisphosphate carboxylase enzyme (Rubisco) showed the strain had high homology with other known rbcL sequences of the genus Chlorella. The strain grows well autotrophically in minimum mineral medium, with a growth rate of 0.28 ± 0.012 day^?1 and a biomass productivity of 138.9 ± 6.7 mg L^?1 day^?1. N‐starvation and/or over illumination with 650 µmol photons m^?2 s^?1 of PAR light on the cultures induced a significant increase in the intracellular content of lipids in this microalga. Total lipids were extracted from the strain biomass with 2:1 chloroform‐methanol, and they accounted for approximately 50% of the dry biomass. Polyunsaturated fatty acids (PUFAs) represented 60.4% of the total fatty acids found in the strain, thus making this biomass attractive as a high added‐value product source. The strain was able to grow efficiently in the refinery treated wastewater from which it was isolated, providing an attractive advantage for further development of more sustainable algal biomass production processes at reduced costs close to a petrol refinery area.     

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.     

Improvement of both lipid and biomass productivities of Qatar Chlorocystis isolate for biodiesel production and food security

Microalgae are considered a very promising alternative for biofuel production. Several strategies were developed to modulate and improve algae metabolites production to meet the requirements for biodiesel production. Most previous research evidenced that the increase of the lipid content is accompanied by a decrease of the biomass production, which increases the cost of the downstream processing. Hence, the challenge is to find special culture conditions that increase the lipid and the biomass productivities simultaneously. In the present work, we developed a strategy for the improvement of biomass and lipid productivities in a novel local microalga isolate, Chlorocystis sp. QUCCCM14, which was not previously known as a promising strain. Indeed, culturing QUCCCM14 using f/2 medium with 10× NaH₂PO₄ (0.15 g L^?1 NaNO₃ and 5.6 mg L^?1 NaH₂PO₄) resulted in an improvement of 3.178 folds the lipid productivity reaching 56.121 mg L^?1 day^?1 and enhanced the biomass productivity reaching 141.363 mg L^?1 day^?1, simultaneously. Comparative analyses of the FAME profiles demonstrated that fed‐batch culture with phosphate or nitrate separately leads to a high production of the omega 3 fatty acids (Linolenic acid), whereas fed‐batch culture with phosphate and nitrate simultaneously increased the production of fatty acids suitable for biodiesel production.     

Effect of aeration and agitation on extractive fermentation of clavulanic acid by using aqueous two‐phase system

In this work, the effects of agitation and aeration rates on aqueous two‐phase system (ATPS)‐based extractive fermentation of clavulanic acid (CA) by Streptomyces variabilis DAUFPE 3060 were investigated through a 2² full factorial design, where oxygen transfer rate (OTR) and oxygen uptake rate (OUR) were selected as the responses. Aeration rates significantly influenced cell growth, OUR, and CA yield, while OTR was practically the same in all the runs. Under the intermediate agitation (950 rpm) and aeration conditions (3.5 vvm) of the central point runs, it was achieved OTR of 1.617 ± 0.049 mmol L^?1 h^?1, OUR of 0.132 ± 0.030 mmol L^?1 h^?1, maximum CA production of 434 ± 4 mg L^?1, oxygen mass transfer coefficient of 33.40 ± 2.01 s^?1, partition coefficient of 66.5 ± 1.5, CA yield in the top and bottom phases of 75% ± 2% and 19% ± 1%, respectively, mass balance of 95% ± 4% and purification factor of 3.8 ± 0.1. These results not only confirmed the paramount role of O₂ supply, broth composition and operational conditions in CA ATPS‐extractive fermentation, but also demonstrated the possibility of effectively using this technology as a cheap tool to simultaneously produce and recover CA. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1444–1452, 2016     

Cultivation of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> with swine wastewater and potential for algal biodiesel production

In this study, an alga-based simultaneous process of treating swine wastewater (SWW) and producing biodiesel was explored. Chlorella vulgaris (UTEX-265) was employed as a model species, and a SWW-based medium was prepared by dilution with tap water. Chlorella vulgaris grew well in the SWW-based medium, and at optimum dilution ratios, it exceeded the conventional culture medium in terms of biomass concentration and productivity. In eightfold diluted SWW, which supported the maximum growth, biomass productivity was 0.247 g L^?1 day^?1, while the productivity was merely 0.165 g L^?1 day^?1 in standard tris-acetate-phosphorous (TAP) algal medium. In addition, fatty acid methyl ester (FAME) productivity was greater in the SWW-based medium (0.067 versus 0.058 g L^?1 day^?1). This enhanced productivity resulted in more than 95 % removal of both nitrogen and phosphorous. All these show that C. vulgaris cultivation is indeed possible in a nutrient-rich wastewater with appropriate dilution, and in so doing, the wastewater can effectively be treated.     

Effect of light emitting diodes on the cultivation of Spirulina platensis using NPK‐10:26:26 complex fertilizer

NPK‐10:26:26 complex fertilizer based culture medium was studied for the mass production of Spirulina platensis using different light emitting diodes (LEDs). First, cultivation was carried out under white LED to formulate the optimum fertilizer loading for which Spirulina growth was maximized. Optimum composition for newly formulated fertilizer medium was NPK fertilizer ?0.76 g L^?1 and sodium bicarbonate ?10.0 g L^?1 and corresponding biomass productivity was found to be 76.67 mg L^?1 day^?1. The effect of different LEDs (for example, blue, white, red, green and yellow) on Spirulina growth kinetics and the accumulation of chlorophyll, protein and lipid content was determined using the optimum NPK fertilizer medium. Kinetic parameters (i.e., biomass productivity, maximum specific growth rate, maximum biomass concentration, nitrogen‐to‐biomass conversion factor and phosphorus‐to‐biomass conversion factor) and chlorophyll accumulation were affected by the use of different LEDs and follow the following trend: blue > white > red > green > yellow, whereas protein and lipid accumulation was almost independent of LEDs used. Elemental C, N, P and K concentrations were measured to find the effects of nutrients for the growth of Spirulina platensis. Physicochemical parameters (pH and conductivity) were also monitored during biomass growth under different LEDs. Finally, biomass growth using NPK‐10:26:26 fertilizer under different LEDs was compared with standard Zarrouk medium and better growth results were obtained using optimally formulated NPK‐10:26:26 fertilizer medium.     

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.     

Investigation of biomass concentration,lipid production,and cellulose content in Chlorella vulgaris cultures using response surface methodology

The microalgae Chlorella vulgaris produce lipids that after extraction from cells can be converted into biodiesel. However, these lipids cannot be efficiently extracted from cells due to the presence of the microalgae cell wall, which acts as a barrier for lipid removal when traditional extraction methods are employed. Therefore, a microalgae system with high lipid productivity and thinner cell walls could be more suitable for lipid production from microalgae. This study addresses the effect of culture conditions, specifically carbon dioxide and sodium nitrate concentrations, on biomass concentration and the ratio of lipid productivity/cellulose content. Optimization of culture conditions was done by response surface methodology. The empirical model for biomass concentration (R² = 96.0%) led to a predicted maximum of 1123.2 mg dw L^?1 when carbon dioxide and sodium nitrate concentrations were 2.33% (v/v) and 5.77 mM, respectively. For lipid productivity/cellulose content ratio (R² = 95.2%) the maximum predicted value was 0.46 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 when carbon dioxide concentration was 4.02% (v/v) and sodium nitrate concentration was 3.21 mM. A common optimum point for both variables (biomass concentration and lipid productivity/cellulose content ratio) was also found, predicting a biomass concentration of 1119.7 mg dw L^?1 and lipid productivity/cellulose content ratio of 0.44 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 for culture conditions of 3.77% (v/v) carbon dioxide and 4.01 mM sodium nitrate. The models were experimentally validated and results supported their accuracy. This study shows that it is possible to improve lipid productivity/cellulose content by manipulation of culture conditions, which may be applicable to any scale of bioreactors. Biotechnol. Bioeng. 2013; 110: 2114–2122. © 2013 Wiley Periodicals, Inc.     

Performance of bioelectrochemical systems inoculated with Desmodesmus sp. A8 under different light sources

Light source can affect the stomata opening, photosynthesis process, and pigment content in microalgae cells. In this study, growth rate, chlorophyll a (chl a) content, and electrogenic capability of Desmodesmus sp. A8 were investigated under incandescent and fluorescent lamps. Growth rate, productivity, and chl a content of strain A8 exposed to incandescent light were recorded as 0.092 ± 0.010 day^?1, 0.019 ± 0.008 g L^?1 day^?1, and 15.10 ± 1.40 mg L^?1, which decreased to 0.086 ± 0.006 day^?1, 0.012 ± 0.004 g L^?1 day^?1, and 10.06 ± 1.59 mg L^?1, respectively, under fluorescent light. The stable current density of bioelectrochemical systems inculcated with strain A8 under incandescent and fluorescent lamps were 249.76 and 158.41 mA m^?2 at ?0.4 V vs. Ag/AgCl, coupling with dissolved oxygen within biofilm decreasing from 15.91 to 10.80 mg L^?1. This work demonstrated that illuminating microalgae under an incandescent lamp can improve biomass production and electrogenic capabilities.     

Key parameters for outdoor biomass production of Scenedesmus obliquus in solar tracked photobioreactors

The biomass productivity of Scenedesmus obliquus was investigated outdoors during all seasons in solar tracked flat panel photobioreactors (PBR) to evaluate key parameters for process optimization. CO₂ was supplied by flue gas from an attached combined block heat and power plant. Waste heat from the power plant was used to heat the culture during winter. The parameters pH, CO₂, and inorganic salt concentrations were automatically adjusted to nonlimiting levels. The optimum biomass concentration increased directly with the photosynthetic active radiation (PAR) from 3 to 5 g dry weight (DW)?L^?1 for a low PAR of 10 mol photons m^?2 day^?1 and high PAR of 40–60 mol photons m^?2 day^?1, respectively. The annual average biomass yield (photosynthetic efficiency) was 0.4?±?0.5 g DW mol^?1 photons. However, biomass yields of 1.5 g DW mol^?1 photons close to the theoretical maximum were obtained at low PAR. The productivity (including the night biomass losses) ranged during all seasons from ?5 up to 30 g DW m^?2 day^?1 with a mean productivity of 9?±?7 g DW m^?2 day^?1. Low night temperatures of the culture medium and elevated day temperatures to the species-specific optimum increased the productivity. Thus, continuous regulation of the biomass concentration and the culture temperature with regard to the fluctuating weather conditions is essential for process optimization of outdoor microalgal production systems in temperate climates.     

Lipid productivity and fatty acid composition in Chlorella and Scenepdesmus strains grown in nitrogen-stressed conditions

Thirty Chlorella and 30 Scenedesmus strains grown in nitrogen-stressed conditions (70 mg L^?1 N) were analyzed for biomass accumulation, lipid productivity, protein, and fatty acid (FA) composition. Scenedesmus strains produced more biomass (4.02?±?0.73 g L^?1) after 14 days in culture compared to Chlorella strains (2.57?±?0.12 g L^?1). Protein content decreased and lipid content increased from days 8 to 14 with an increase in triacylglycerol (TAG) accumulation in most strains. By day 14, Scenedesmus strains generally had higher lipid productivity (53.5?±?3.7 mg lipid L^?1 day^?1) than Chlorella strains (35.1?±?2.8 mg lipid L^?1 day^?1) with the lipids consisting mainly of C16–18 TAGs. Scenedesmus strains generally had a more suitable FA profile with higher amounts of saturated fatty acids and monounsaturated fatty acids (MUFAs) and a smaller polyunsaturated fatty acid (PUFA) component. Chlorella strains had a larger PUFA component and smaller MUFA component. The general trend in the FA composition of Chlorella strains was oleic > palmitic > α-linolenic = linoleic > eicosenoic > heptadecenoic > stearic acid. For Scenedesmus strains, the general trend was oleic > palmitic > linoleic > α-linolenic > stearic > eicosenoic > palmitoleic > heptadecenoic acid. The most promising strains with the highest lipid productivity and most suitable FA profiles were Scenedesmus sp. MACC 401, Scenedesmus soli MACC 721, and Scenedesmus ecornis MACC 714. Although Chlorella sp. MACC 519 had lower lipid productivity, the FA profile was good with a lower PUFA component compared to the other Chlorella strains analyzed and a low linolenic acid concentration.     

Production of Chlorella vulgaris as a source of essential fatty acids in a tubular photobioreactor continuously fed with air enriched with CO2 at different concentrations

To reduce CO₂ emissions and simultaneously produce biomass rich in essential fatty acids, Chlorella vulgaris CCAP 211 was continuously grown in a tubular photobioreactor using air alone or air enriched with CO₂ as the sole carbon source. While on one hand, nitrogen‐limited conditions strongly affected biomass growth, conversely, they almost doubled its lipid fraction. Under these conditions using air enriched with 0, 2, 4, 8, and 16% (v/v) CO₂, the maximum biomass concentration was 1.4, 5.8, 6.6, 6.8, and 6.4 g_DB L^?1 on a dry basis, the CO₂ consumption rate 62, 380, 391, 433, and 430 L^?1 day^?1, and the lipid productivity 3.7, 23.7, 24.8, 29.5, and 24.4 mg L^?1 day^?1, respectively. C. vulgaris was able to grow effectively using CO₂‐enriched air, but its chlorophyll a (3.0–3.5 g 100g_DB^?1), chlorophyll b (2.6–3.0 g 100g_DB^?1), and lipid contents (10.7–12.0 g 100g_DB^?1) were not significantly influenced by the presence of CO₂ in the air. Most of the fatty acids in C. vulgaris biomass were of the saturated series, mainly myristic, palmitic, and stearic acids, but a portion of no less than 45% consisted of unsaturated fatty acids, and about 80% of these were high added‐value essential fatty acids belonging to the ω3 and ω6 series. These results highlight that C. vulgaris biomass could be of great importance for human health when used as food additive or for functional food production. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:916–922, 2014     

Effects of different nitrogen, phosphorus, and iron concentrations and salinity on lipid production in newly isolated strain of the tropical green microalga, Scenedesmus dimorphus KMITL

The fatty acid composition, the effect of different concentrations of nitrogen (16.5-344 mg ?L^?1), phosphorus (9–45 mg? L^?1), iron (9–45 mg? L^?1) and salinity levels (0–20 psu) on lipid production in the green microalga Scenedesmus dimorphus KMITL, a new strain isolated from a tropical country, Thailand, were studied. The alga was isolated from a freshwater fish pond, and cultured in Chlorella medium by varying one parameter at a time. The main fatty acid composition of this strain was C16–C18 (97.52 %) fatty acids. A high lipid content was observed in conditions of 16.5 mg? L^?1-N, or 22 mg ?L^?1-P, or 45 mg ?L^?1-Fe, or 5 psu salinity, which accumulated lipids to 20.3?±?0.4, 19.4?±?0.2, 24.7?±?0.5, and 14.3?±?0.2 % of algal biomass, respectively. Increasing lipid content and lipid productivity was noted when the alga was cultured under high iron concentration and high salinity, as well as under reduced phosphorus conditions, whereas nitrogen limitation only resulted in an increased lipid content.     

Lipid and total fatty acid productivity in photoautotrophic fresh water microalgae: screening studies towards biodiesel production

Microalgae are considered as a promising feedstock for biomass production. The selection of the most suitable species is based on several key parameters such as lipid and fatty acid productivity. In the present study, the growth of different microalgae strains was examined in freshwater media for photoautotrophs suited for large-scale applications to identify the most suitable medium for each species. In the optimal medium, Scenedesmus obliquus showed the highest biomass productivity measured as increase of cell dry weight (0.25 g cellu dry weight (CDW) L^?1 day^?1), while Botryococcus braunii showed the highest lipid and total fatty acid content (430 and 270 mg g^?1 CDW, respectively) among the tested species. Regarding lipid and total fatty acid productivity, S. obliquus was the most lipid and total fatty acid productive strain with 41 and 18 mg L^?1 day^?1 during the exponential phase, respectively. Additionally, the proportion of saturated and monounsaturated fatty acids increased with duration of the incubation in S. obliquus, while polyunsaturated fatty acids decreased. These results nominate S. obliquus as a promising microalga in order to serve as a feedstock for renewable energy production.     

Interspecific biodiversity enhances biomass and lipid productivity of microalgae as biofuel feedstock

Large improvements in biomass and lipid production are required to make massive scale algal biodiesel production an economic reality. The application of the biodiversity strategy to enhance algal biomass as biofuel feedstock is little. The algal diversity was manipulated in this study to investigate the effects of a combination of biodiversity complementarity and a new medium consisting of seawater and agricultural fertilizer on lipid productivity. The algae diverse community includes two strains of Dunaliella salina (Dunaliella salina 19/30 and 19/18) and three species of Nannochloropsis (Nannochloropsis oculata, Nannochloropsis salina, and Nannochloropsis gaditana). The results showed that the most diverse community (5 species) produced an average of sixfold more biomass in the new medium than did the standard f/2 culture medium. The most diverse polyculture had the highest growth rate (1.01 day^?1), biomass (1.2 g L^?1), and lipid productivity (0.31 g L^?1 day^?1). The assessment of algal polycultures relative to monocultures is particularly interesting and novel for this biofuel field, and the observations that these polycultures resulted in significant lipid productivity improvements are very useful addition to the biofuel research. The possible mechanism (resource diversity) to explain the synergy in mixed cultures warrants further investigation.     

Utilization of cane molasses towards cost-saving astaxanthin production by a Chlorella zofingiensis mutant

The aim of the present study was to survey the growth and astaxanthin production of E17, an astaxanthin-rich mutant of Chlorella zofingiensis, through feeding the low-cost carbon source cane molasses. In heterotrophic batch cultivation, E17 fed with pretreated molasses achieved biomass (1.79 g L^?1 day^?1) and astaxanthin (1.99 mg L^?1 day^?1) productivities comparable to those with glucose, which were about 2- and 2.8-fold of those fed with untreated molasses, respectively. Molasses-induced astaxanthin accumulation may be attributed to the elicited expression of carotenogenic genes, in particular the genes specifically responsible for the ketolation and hydroxylation of β-carotene to form astaxanthin. A two-stage fed-batch strategy was employed to grow E17 and induce astaxathin accumulation, resulting in 45.6 g L^?1 biomass and 56.1 mg L^?1 astaxanthin, the highest volumetric astaxanthin yield ever reported for this alga. In addition, the astaxanthin production by E17 was tested with a semi-continuous culture method, where the directly diluted raw molasses (giving 5 g L^?1 sugar) was used as the carbon source. Little growth inhibition of E17 was observed in the semi-continuous culture with a biomass productivity of 1.33 g L^?1 day^?1 and an astaxanthin productivity of 0.83 mg L^?1 day^?1. The mixotrophic semi-continuous cultures enhanced the biomass and astaxanthin productivities by 29.3 % and 42.2 %, respectively. This study highlights the potential of using the industrially cheap cane molasses towards large-scale cost-saving production of the high-value ketocarotenoid astaxanthin.