Productivity and biochemical composition of <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> and <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>: effects of different cultivation approaches

The present work evaluated biomass productivity, carbon dioxide fixation rate, and biochemical composition of two microalgal species, Phaeodactylum tricornutum (Bacillariophyta) and Tetradesmus obliquus (Chlorophyta), cultivated indoors in high-technology photobioreactors (HT-PBR) and outdoors both in pilot ponds and low-technology photobioreactors in a greenhouse in southern Italy. Microalgae were grown in standard media, under nitrogen starvation, and in two liquid digestates obtained from anaerobic digestion of agro-zootechnical and vegetable biomass. P. tricornutum, cultivated in semi-continuous mode in indoor HT-PBRs with standard medium, showed a biomass productivity of 21.0?±?2.3 g m^?2 d^?1. Applying nitrogen starvation, the lipid productivity increased from 2.3 up to 4.5?±?0.5 g m^?2 d^?1, with a 24 % decrease of biomass productivity. For T. obliquus, a biomass productivity of 9.1?±?0.9 g m^?2 d^?1 in indoor HT-PBR was obtained using standard medium. Applying liquid digestates as fertilizers in open ponds, T. obliquus gave a biomass productivity (10.8?±?2.0 g m^?2 d^?1) not statistically different from complete medium such as P. tricornutum (6.5?±?2.2 g m^?2 d^?1). The biochemical data showed that the fatty acid composition of the microalgal biomass was affected by the different cultivation conditions for both microalgae. In conclusion, it was found that the microalgal productivity in standard medium was about doubled in HT-PBR compared to open ponds for P. tricornutum and was about 20 % higher for T. obliquus.     

Utilization of gaseous emissions from a methanol plant for cultivation of <Emphasis Type="Italic">Acutodesmus obliquus</Emphasis>

This study aimed to culture the green alga Acutodesmus obliquus utilizing the gaseous emissions containing a high concentration of CO₂ (99.13 %) from a methanol plant and study the tolerance of microalgae. The effect of CO₂ concentration, aeration rate, inoculum concentration, intermittent sparging, and nitrogen sources on the growth of A. obliquus was examined. Acutodesmus obliquus also was cultivated in a 500-L pilot outdoor tubular photobioreactor (OTP) to advance the laboratory scale system to outdoor scale-up applications. The results showed that A. obliquus could tolerate high CO₂ concentrations of 50 %, and a maximum biomass of 0.935 g L^?1 (dry weight) was achieved at 20 % CO₂. An aeration rate of 500 mL min^?1, inoculum concentration (optical density at 680 nm [OD₆₈₀]?=?0.3), and intermittent sparging of 10 min per 2 h enhanced growth to the optimum and influenced culture pH and photosynthesis. Urea as a nitrogen source was shown to be more beneficial to cell growth. A urea concentration of 0.3 g L^?1 and an N/P ratio of 15 led to maximum biomass accumulation thus enhancing the gaseous emission utilization efficiency. In conclusion, this work demonstrated that gaseous emissions containing high concentration of CO₂ from a methanol plant could be directly introduced into A. obliquus cultures and that A. obliquus was suitable well for large-scale outdoor cultivation in a tubular photobiorecator.     

Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1 % (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2 % (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 μmol m^?2s^?1 for Chlorella sp. (22.5 %) and S. obliquus R8 (23.7 %) and 80 μmol m^?2s^?1 for C. vulgaris CCAP211/11B (20.1 %) and B. braunii FC124 (34.9 %).     

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.     

Growing microalgae as aquaculture feeds on twin-layers: a novel solid-state photobioreactor

Four strains of marine microalgae commonly used as live feeds in hatcheries (Isochrysis sp. T.ISO, Tetraselmis suecica, Phaeodactylum tricornutum, Nannochloropsis sp.) were grown in a novel solid-state photobioreactor, the twin-layer system. Microalgae were immobilized by self adhesion to vertically oriented twin-layer modules which consisted of two different types of ultrathin layers, a macroporous source layer (glass fiber nonwoven) through which the culture medium was transported by gravity flow, and a microporous substrate layer (plain printing paper) which carried the algae on both surfaces of the source layer. This simple open cultivation system effectively separated the immobilized microalgae from the bulk of the growth medium and permitted prolonged cultivation of microalgae with average biomass yields of 10–15 g dry weight m^?2 growth area after 14–25 days of cultivation. Algal biomass was harvested as fresh weight (with 72–84 % water content) without the need to pre-concentrate algae. No aeration or external CO₂ supply was necessary, and due to the microporous substrate layer, no eukaryotic contaminations were observed during the experiment. All experiments were conducted in Germany under greenhouse conditions with natural sunlight. Small-scale growth experiments performed under the same conditions revealed that growth over most of the experimental period (24 days) was linear in all tested algae with growth rates (dry weight per square meter growth area) determined to be 0.6 g ?m^?2?day^?1 (Isochrysis), 0.8 g? m^?2?day^?1 (Nannochloropsis), 1.5 g ?m^?2?day^?1 (Tetraselmis), and 1.8 g? m^?2?day^?1 (Phaeodactylum). Due to its cost-effective construction and with further optimisation of design and productivity at technical scales, the twin-layer system may provide an attractive alternative to methods traditionally used to cultivate live microalgae.     

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.     

Effects of various LED light wavelengths and light intensity supply strategies on synthetic high-strength wastewater purification by Chlorella vulgaris

Chemical fertilizer agricultural wastewater is a typical high-strength wastewater that has dramatically triggered numerous environmental problems in China. The Chlorella vulgaris microalgae biological wastewater treatment system used in this study can effectively decontaminate the high-strength carbon and nitrogen wastewater under an optimum light wavelength and light intensity supply strategy. The descending order of both the dry weight for C. vulgaris reproduction and wastewater nutrient removal efficiency is red > white > yellow > purple > blue > green, which indicates that red light is the optimum light wavelength. Furthermore, rather than constant light, optimal light intensity is used for the incremental light intensity strategy. The phases for the optimal light intensity supply strategy are as follows: Phase 1 from 0 to 48 h at 800 μmol m^?2 s^?1; Phase 2 from 48 to 96 h at 1,200 μmol m^?2 s^?1; and Phase 3 from 96 to 144 h at 1,600 μmol m^?2 s^?1. Additionally, the optimal cultivation time is 144 h.     

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.     

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.     

Optimisation of biomass and lipid production by adjusting the interspecific competition mode of Dunaliella salina and Nannochloropsis gaditana in mixed culture

The high cost of algal cultivation has been a barrier associated with the commercialisation of algal biodiesel. Therefore, this study aimed to enhance lipid production by optimising the nutrient supply to benefit the coexistence of Dunaliella salina and Nannochloropsis gaditana. The effects on biomass and lipid production of using different proportions of D. salina and N. gaditana, urea and NaHCO₃ were optimised by response surface method with a 17-run Box–Behnken design. The optimal conditions for the algal growth are 58 % of D. salina in the mixture at OD₆₈₀, 150 μL day^?1 urea (0.0044 g day^?1) and no addition of NaHCO₃. The biomass concentration and lipid production reached 1.00 and 0.383 g L^?1, respectively, which are exceeded by the amount before optimisation, indicating the efficiency of the model obtained by response surface method.     

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.     

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.     

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.     

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.     

Fed-Batch Cultivation of Arthrospira platensis Using Carbon Dioxide from Alcoholic Fermentation and Urea as Carbon and Nitrogen Sources

To reduce CO₂ emissions from alcoholic fermentation, Arthrospira platensis was cultivated in tubular photobioreactor using either urea or nitrate as nitrogen sources at different light intensities (60 μmol m^?2 s^?1?≤?I?≤?240 μmol m^?2 s^?1). The type of carbon source (pure CO₂ or CO₂ from fermentation) did not show any appreciable influence on the main cultivation parameters, whereas substitution of nitrate for urea increased the nitrogen-to-cell conversion factor (Y _X/N ), and the maximum cell concentration (X _m ) and productivity (P _X ) increased with I. As a result, the best performance using gaseous emissions from alcoholic fermentation (X _m ?=?2,960?±?35 g m^?3, P _X ?=?425?±?5.9 g m^?3 day^?1 and Y _X/N ?=?15?±?0.2 g g^?1) was obtained at I?=?120 μmol m^?2 s^?1 using urea as nitrogen source. The results obtained in this work demonstrate that the combined use of effluents rich in urea and carbon dioxide could be exploited in large-scale cyanobacteria cultivations to reduce not only the production costs of these photosynthetic microorganisms but also the environmental impact associated to the release of greenhouse emissions.     

Microalgal cultivation in porous substrate bioreactor for extracellular polysaccharide production

Netrium digitus is a representative of the species-rich class Zygnematophyceae (Streptophyta). Its intensive extracellular polysaccharide (EPS) production makes this alga interesting for biotechnological applications with a focus on cosmetics and food additives. Quantitative data on growth and EPS production in suspension and, for the first time, in immobilized culture using lab-scale porous substrate bioreactors, so-called Twin-Layer (TL) systems, is presented. It is shown that the cell as well as the EPS dry weight content is increased at least sixfold in immobilized compared to suspension culture. Due to the high amount of EPS, the biofilms reach a thickness of more than 8 mm after 27 days at 70 μmol photons m^?2 s^?1 and with 1.5% CO₂ supply. Frequent exchange of the growth medium results in a linear cell biomass increase of 2.02?±?0.09 g m^?2 growth area day^?1 compared to 2.99?±?0.09 g m^?2 day^?1, when the medium is not exchanged. Under this mode of cultivation, the EPS production is lower and a final concentration of 12.18?±?1.25 g m^?2 compared to 20.76?±?0.85 g m^?2, when medium was exchanged, is reached. It is clearly demonstrated that the relatively slow growing, but excessively EPS producing, microalgal species N. digitus can be grown in porous substrate bioreactors and that this culturing technique is a promising alternative to suspension culture for the Zygnematophyceae.     

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.     

Intermittent aeration affects the bioremediation potential of two red algae cultured in finfish effluent

The high cost of aeration needed to tumble culture macroalgae is a limiting factor for integration with land-based finfish culture. Toward reducing this electricity cost, we compared intermittent aeration (16 h on:8 h off) with continuous aeration (24 h on) on the productivity of two strains of Chondrus crispus (Basin Head and Charlesville) and Palmaria palmata from Atlantic Canada between May and June 2011. Algal fronds were cultured under a 16:8-h light/dark photoperiod in 50-L tanks supplied with finfish effluent (49 μmol L^?1 of ammonium and 11 μmol L^?1 of phosphate) at a mean water flow rate of 0.4 L min^?1. Nitrogen (N) influx was 1.8 gN m^?2 day^?1, and phosphorus (P) influx was 0.9 gP m^?2 day^?1, with uptake rates ranging from 0.02 to 2.4 gN m^?2 day^?1 and ?0.2 to 0.4 gP m^?2 day^?1. On average, the macroalgae culture system (algae and biofilms) removed 1.0 gN m^?2 day^?1 (51.9 %). The growth of macroalgae (pooled across treatment and strain) ranged from 0.5 to 1.6 % day^?1, which accounted for a yield of 2.2 to 5.4 g DW m^?2 day^?1. Switching off aeration at night improved the growth rate of Basin Head Chondrus by 146 % and had no effect on growth rate or nitrogen and carbon removal by P. palmata and Charlesville Chondrus. Growth and yield of Basin Head Chondrus under intermittent aeration were over two times greater than both Charlesville Chondrus treatments.     

Withanolide A production from Withania somnifera hairy root cultures with improved growth by altering the concentrations of macro elements and nitrogen source in the medium

Withania somnifera is an important medicinal plant that contains withanolides as bioactive compounds. We have investigated the effects of macroelements and nitrogen source in hairy roots of W. somnifera with the aim of optimizing the production of biomass and withanolide A content. The effects of the macroelements NH₄NO₃, KNO₃, CaCl₂, MgSO₄ and KH₂PO₄ at concentrations of 0, 0.5, 1.0, 1.5 and 2.0× strengths and of nitrogen source [NH₄ ⁺/NO₃ ^? (0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20 and 14.38/37.60 mM)] in Murashige and Skoog medium were evaluated for biomass and withanolide A production. The highest accumulation of biomass (139.42 g l^?1 FW and 13.11 g l^?1 DW) was recorded in the medium with 2.0× concentration of KH₂PO₄, and the highest production of withanolide A was recorded with 2.0× KNO₃ (15.27 mg g^?1 DW). The NH₄ ⁺/NO₃ ^? ratio also influenced root growth and withanolide A production, with both parameters being larger when the NO₃ ^? concentration was higher than that of NH₄ ⁺. Maximum biomass growth (148.17 g l^?1 FW and 14.79 g l^?1 DW) was achieved at NH₄ ⁺/NO₃ ^? ratio of 14.38/37.60 mM, while withanolide A production was greatest (14.68 mg g^?1 DW) when the NH₄ ⁺/NO₃ ^? ratio was 0.00/18.80 mM. The results are useful for the large scale cultivation of Withania hairy root culture for the production of withanolide A.     

Truncated light-harvesting chlorophyll antenna size in <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> improves biomass productivity

Microalgae have been proposed as eco-friendly feedstocks for biodiesel production, because they accumulate large amounts of lipids and increase their biomass through photosynthesis. However, the photosynthetic efficiency of microalgae is too low for this strategy to be economically feasible. In an effort to overcome this issue, random mutants with reduced chlorophyll antenna size were generated by ethyl methanesulfonate (EMS)-mediated mutagenesis of Chlorella vulgaris. The antenna size mutant, herein designated E5, exhibited 56.5 and 75.8 % decreases in chlorophyll a and b contents, respectively, with significant reductions in the expression levels of peripheral light-harvesting antenna proteins in photosystem II. The saturated photosynthetic activity and electron transport rate of the E5 mutant were significantly higher and also showed reduced non-photochemical quenching (NPQ), compared to those of the wild type. Consequentially, the E5 mutant cultures achieved 44.5 % improvement in biomass productivity under high light (200 μmol photons m^?2 s^?1). These results suggest that improving the photosynthetic efficiency of microalgae could greatly enhance their biomass production, and such mutant strains can be applicable for large-scale outdoor cultivation which is typically exposed to high light intensity.