Enhancement of total lipid yield by nitrogen,carbon, and iron supplementation in isolated microalgae

The biochemical contents and biodiesel production ability of three microalgal strains grown under different sodium nitrate, sodium carbonate, and ferric ammonium citrate (iron) levels were investigated. The highest biomass and lipid contents were found in Scenedesmus sp., Chlorella sp., and Chlamydomonas sp. when grown in normal BG‐11 containing sodium carbonate concentration at 0.03 g · L^?1, and in normal BG‐11 containing iron concentration (IC) at 0.009 or 0.012 g · L^?1. Increasing the sodium nitrate level increased the biomass content, but decreased the lipid content in all three microalgae. Among the three microalgae, Scenedesmus sp. showed the highest total lipid yield of 0.69 g · L^?1 under the IC of 0.012 g · L^?1. Palmitic and oleic acids were the major fatty acids of Scenedesmus sp. and Chlamydomonas sp. lipids. On the other hand, Chlorella sp. lipids were rich in palmitic, oleic, and linolenic acids, and henceforth contributing to poor biodiesel properties below the standard limits. The three isolated strains had a potential for biodiesel production. Nevertheless, Scenedesmus sp. from stone quarry pond water was the most suitable source for biodiesel production with tolerance toward the high concentration of sodium carbonate without the loss of its biodiesel properties.     

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.     

Evaluation of antioxidant capacities of green microalgae

Three strains of green microalgae, Chlorococcum sp.C53, Chlorella sp. E53, and Chlorella sp.ED53 were studied for their antioxidant activities. Crude extracts of these microalgae in hot water and in ethanol were examined for their total phenolic contents and for their antioxidant capacities. In order to determine their phenolic contents, the Folin–Ciocalteu method was used. As for the determination of their antioxidant capacities, four different assays were used: (1) total antioxidant capacity determination; (2) DPPH radical scavenging assay; (3) ferrous ion chelating ability assay; and (4) inhibition of lipid peroxidation (using thiobarbituric acid reactive substance). For all the strains we have studied, their ethanolic extract showed more antioxidant activities than their hot water extract. Categorically, the ethanolic extract of Chlorella sp.E53 exhibited both the highest total phenolic content of 35.5?±?0.14 mg gallic acid equivalent (GAE) g^?1 dry weight and the highest DPPH radical scavenging of 68.18?±?0.38 % at 1.4 mg mL^?1 (IC₅₀ 0.81 mg mL^?1), whereas Chlorella sp.ED53 showed both the highest ferrous ion chelation activity of 42.78?±?1.48 % at 1 mg mL^?1 (IC₅₀ 1.23 mg mL^?1) and the highest inhibition of lipid peroxidation of 87.96?±?0.59 % at 4 mg mL^?1. This high level of inhibition is comparable to 94.42?±?1.39 % of butylated hydroxytoluene, a commercial synthetic antioxidant, at the same concentration.     

Carbon allocation under light and nitrogen resource gradients in two model marine phytoplankton1

Marine phytoplankton have conserved elemental stoichiometry, but there can be significant deviations from this Redfield ratio. Moreover, phytoplankton allocate reduced carbon (C) to different biochemical pools based on nutritional status and light availability, adding complexity to this relationship. This allocation influences physiology, ecology, and biogeochemistry. Here, we present results on the physiological and biochemical properties of two evolutionarily distinct model marine phytoplankton, a diatom (cf. Staurosira sp. Ehrenberg) and a chlorophyte (Chlorella sp. M. Beijerinck) grown under light and nitrogen resource gradients to characterize how carbon is allocated under different energy and substrate conditions. We found that nitrogen (N)‐replete growth rate increased monotonically with light until it reached a threshold intensity (~200 μmol photons · m^?2 · s^?1). For Chlorella sp., the nitrogen quota (pg · μm^?3) was greatest below this threshold, beyond which it was reduced by the effect of N‐stress, while for Staurosira sp. there was no trend. Both species maintained constant maximum quantum yield of photosynthesis (mol C · mol photons^?1) over the range of light and N‐gradients studied (although each species used different photophysiological strategies). In both species, C:chl a (g · g^?1) increased as a function of light and N‐stress, while C:N (mol · mol^?1) and relative neutral lipid:C (rel. lipid · g^?1) were most strongly influenced by N‐stress above the threshold light intensity. These results demonstrated that the interaction of substrate (N‐availability) and energy gradients influenced C‐allocation, and that general patterns of biochemical responses may be conserved among phytoplankton; they provided a framework for predicting phytoplankton biochemical composition in ecological, biogeochemical, or biotechnological applications.     

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.     

Bioremediation Potential of Chlorella: Spectroscopic,Kinetics, and Sem Studies

A dead dried alga, Chlorella sp., was used for the uptake of Cr⁺³, Cr₂O₇ ^?2, Cu⁺², and Ni⁺² from the aqueous solutions of these metal ions. The equilibrium data were fitted using the Langmuir and Freundlich isotherm model and the maximum uptakes for Cr⁺³, Cr₂O₇ ^?2, Ni⁺², and Cu⁺² were 98, 104, 108, and 183 mg/g, respectively. The Freundlich model, in comparison to the Langmuir model, better represented the sorption process. The kinetics of metal ions uptake by Chlorella sp. was best described by a pseudo-second order rate equation. Infrared spectroscopic data were employed to identify the site(s) of bonding in Chlorella sp. A scanning electron microscopic (SEM) study of pure dead Chlorella sp. and the species treated with different metal ions provided an idea of the extent of metal uptake by this species. The dead Chlorella sp took up maximum Cu(II). The size of the cell of the metal-treated Chlorella sp. obtained from SEM data is in agreement with the extent of metal uptake.     

Different fermentation strategies by Schizochytrium mangrovei strain pq6 to produce feedstock for exploitation of squalene and omega‐3 fatty acids

Schizochytrium mangrovei strain PQ 6 was investigated for coproduction of docosahexaenoic acid (C22: 6ω‐3, DHA ) and squalene using a 30‐L bioreactor with a working volume of 15 L under various batch and fed‐batch fermentation process regimes. The fed‐batch process was a more efficient cultivation strategy for achieving higher biomass production rich in DHA and squalene. The final biomass, total lipid, unsaponifiable lipid content, and DHA productivity were 105.25 g · L^?1, 43.40% of dry cell weight, 8.58% total lipid, and 61.66 mg · g^?1 · L^?1, respectively, after a 96 h fed‐batch fermentation. The squalene content was highest at 48 h after feeding glucose (98.07 mg · g^?1 of lipid). Differences in lipid accumulation during fermentation were correlated with changes in ultrastructure using transmission electron microscopy and Nile Red staining of cells. The results may be of relevance to industrial‐scale coproduction of DHA and squalene in heterotrophic marine microalgae such as Schizochytrium .     

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

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

Enzymatic pre‐treatment of microalgae cells for enhanced extraction of proteins

Crude proteins and pigments were extracted from different microalgae strains, both marine and freshwater. The effectiveness of enzymatic pre‐treatment prior to protein extraction was evaluated and compared to conventional techniques, including ultrasonication and high‐pressure water extraction. Enzymatic pre‐treatment was chosen as it could be carried out at mild shear conditions and does not subject the proteins to high temperatures, as with the ultrasonication approach. Using enzymatic pre‐treatment, the extracted proteins yields of all tested microalgae strains were approximately 0.7 mg per mg of dry cell weight. These values were comparable to those achieved using a commercial lytic kit. Ultrasonication was not very effective for proteins extraction from Chlorella sp., and the extracted proteins yields did not exceed 0.4 mg per mg of dry cell weight. For other strains, similar yields were achieved by both treatment methods. The time‐course effect of enzymatic incubation on the proteins extraction efficiency was more evident using laccase compared to lysozyme, which suggested that the former enzyme has a slower rate of cell disruption. The crude extracted proteins were fractionated using an ion exchange resin and were analyzed by the electrophoresis technique. They were further tested for their antioxidant activity, the highest of which was about 60% from Nannochloropsis sp. The total phenolic contents in the selected strains were also determined, with Chlorella sp. showing the highest content reaching 17 mg/g. Lysozyme was also found to enhance the extraction of pigments, with Chlorella sp. showing the highest pigments contents of 16.02, 4.59 and 5.22 mg/g of chlorophyll a, chlorophyll b and total carotenoids, respectively.     

Biodegradation of nicotine by a newly isolated Agrobacterium sp. strain S33

Aims: To isolate and characterize bacteria capable of degrading nicotine from the rhizospheric soil of a tobacco plant and to use them to degrade the nicotine in tobacco solid waste. Methods and Results: A bacterium, strain S33, was newly isolated from the rhizospheric soil of a tobacco plant, and identified as Agrobacterium sp. based on morphology, physiological tests, Biolog MicroLog3 4·20 system and 16S rRNA gene sequence. Using nicotine as the sole source of carbon and nitrogen in the medium, it grew optimally with 1·0 g l^?1 of nicotine at 30°C and pH 7·0, and nicotine was completely degraded within 6 h. The resting cells prepared from the glucose‐ammonium medium or LB medium could not degrade nicotine within 10 h, while those prepared from the nicotine medium could completely degrade 3 g l^?1 of nicotine in 1·5 h at a maximal rate of 1·23 g nicotine h^?1 g^?1 dry cell. Using the medium containing nicotine, glucose and ammonium simultaneously to cultivate strain S33, the resting cells could degrade 98·87% of nicotine in tobacco solid waste with the concentration as 30 mg nicotine g^?1 dry weight tobacco solid waste within 7 h at a maximal rate of 0·46 g nicotine h^?1 g^?1 dry cell. Conclusions: This is the first report that Agrobacterium sp. has the ability to degrade nicotine. Agrobacterium sp. S33 could use nicotine as the sole source of carbon and nitrogen. The use of resting cells of the strain S33 prepared from the nicotine–glucose–ammonium medium was an effective method to degrade nicotine and detoxify tobacco solid waste. Significance and Impact of the Study: Nicotine in tobacco wastes is both toxic and harmful to human health and the environment. This study showed that Agrobacterium sp. S33 may be suitable for the disposal of tobacco wastes and reducing the nicotine content in tobacco leaves.     

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

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

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 %).     

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.     

ROLE OF GLUTAMATE DEHYDROGENASE AND GLUTAMINE SYNTHETASE IN CHLORELLA VULGARIS DURING ASSIMILATION OF AMMONIUM WHEN JOINTLY IMMOBILIZED WITH THE MICROALGAE‐GROWTH‐PROMOTING BACTERIUM AZOSPIRILLUM BRASILENSE1

Enzymatic activities of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) participating in the nitrogen metabolism and related ammonium absorption were assayed after the microalga Chlorella vulgaris Beij. was jointly immobilized with the microalgae‐growth‐promoting bacterium Azospirillum brasilense. At initial concentrations of 3, 6, and 10 mg · L^?1 NH₄⁺, joint immobilization enhances growth of C. vulgaris but does not affect ammonium absorption capacity of the microalga. However, at 8 mg · L^?1 NH₄⁺, joint immobilization enhanced ammonium absorption by the microalga without affecting the growth of the microalgal population. Correlations between absorption of ammonium per cell and per culture showed direct (negative and positive) linear correlations between these parameters and microalga populations at 3, 6, and 10 mg · L^?1 NH₄⁺, but not at 8 mg · L^?1 NH₄⁺, where the highest absorption of ammonium occurred. In all cultures, immobilized and jointly immobilized, having the four initial ammonium concentrations, enzymatic activities of Chlorella are affected by A. brasilense. Regardless of the initial concentration of ammonium, GS activity in C. vulgaris was always higher when jointly immobilized and determined on a per‐cell basis. When jointly immobilized, only at an initial concentration of 8 mg · L^?1 NH₄⁺ was GDH activity per cell higher.     

Cell disruption methods for improving lipid extraction efficiency in unicellular microalgae

Identification of cost‐effective cell disruption methods to facilitate lipid extraction from microalgae represents a crucial step in identifying promising biofuel‐producing species. Various cell disruption methods including autoclaving, microwave, osmotic shock, and pasteurization were tested in the microalgae Chlorococcum sp. MCC30, Botryococcus sp. MCC31, Botryococcus sp. MCC32, and Chlorella sorokiniana MIC‐G5. Lipid content (on dry weight basis) from the four cultures on day 7 ranged from 11.15 to 48.33%, and on day 14 from 11.42 to 44.26%. Among the methods tested, enhanced lipid extraction was achieved through osmotic shock (15% NaCl) for Botryococcus sp. MCC32, microwave (6 min) for Botryococcus sp. MCC31, osmotic shock (5% NaCl) for Chlorella sorokiniana MIC‐G5 and microwave (2 min) for Chlorococcum sp. MCC30. The highest palmitate (16:0) contents (25.64% and 34.20%) were recorded with osmotic shock (15% NaCl) treatment for Botryococcus sp. MCC32 and microwave (6 min) for Botryococcus sp. MCC31, respectively. Two strains, along with their respective cell disruption methods, were identified as promising oil blends or nutraceuticals due to their high unsaturated fatty acid (UFA) content: Botryococcus sp. MCC31 (37.6% oleic acid content; 39.37% UFA) after autoclaving and Botryococcus sp. MCC32 after osmotic shock of 15% NaCl treatment (19.95% oleic acid content; 38.17% UFA).     

Phycoremediation resultant lipid production and antioxidant changes in green microalgae Chlorella Sp.

In this investigation, we report on the treatment of tannery wastewater using microalgae Chlorella species to produce lipid and fatty acid as well as changes in antioxidant metabolism during the treatment. The variation in growth, production of pigments, antioxidant metabolism, lipid and fatty acids, and nutrient removal from wastewater during the remediation were observed. Surprisingly, a profuse growth was found in 50% diluted tannery wastewater (TW), which supported to accumulate high yield of lipid (18.5%) and unsaturated fatty acids (50.05%). The antioxidant activity of microalgae in both the concentrations (50% and 100% TW) were viz., lipid peroxidation 1.6 ± 0.1 and 2.3 ± 0.02nmol MDA mg^?1 protein, SOD 10.3 ± 0.4 and 15.7 ± 0.9 U mg^?1 protein, CAT 0.17 ± 0.036 and 0.52 ± 0.06 U mg^?1 protein, and APX 7.2 ± 0.8 and 11.2 ± 09 U mg^?1 protein respectively, which point out that the free radical scavenging mechanism against heavy metal stress. Maximum phycoremediation of heavy metals observed from both concentrations during the healthy growth period were Cr – 73.1, 45.7%, Cu – 90.4, 78.1%, Pb – 92.1, 52.2%, and Zn – 81.2, 44.6%, respectively. This study proved the potential use of Chlorella for heavy metal and nutrient removal from tannery wastewater. Moreover, an unaffected growth with high antioxidant activity of this species promises a sustainable lipid and fatty acid contents for biofuel production.     

Antioxidant activity and phenolic profile in filamentous cyanobacteria: the impact of nitrogen

In the present study, ethanolic extracts of ten cyanobacterial strains cultivated under different nitrogen conditions were assessed for the phenolic content and antioxidant activity. The amount of detected phenolic compounds ranged from 14.86 to 701.69 μg g^?1 dry weight (dw) and HPLC-MS/MS analysis revealed gallic acid, chlorogenic acid, quinic acid, catechin, epicatechin, kaempferol, rutin and apiin. Only catechin, among the detected phenolics, was present in all the tested strains, while quinic acid was the most dominant compound in all the tested Nostoc strains. The results also indicated the possibility of increasing the phenolic content in cyanobacterial biomass by manipulating nitrogen conditions, such as in the case of quinic acid in Nostoc 2S7B from 70.83 to 594.43 μg g^?1 dw. The highest radical scavenging activity in DPPH assay expressed Nostoc LC1B with IC₅₀ value of 0.04?±?0.01 mg mL^?1, while Nostoc 2S3B with IC₅₀ =?9.47?±?3.61 mg mL^?1 was the least potent. Furthermore, the reducing power determined by FRAP assay ranged from 8.36?±?0.08 to 21.01?±?1.66 mg AAE g^?1, and it was significantly different among the tested genera. The Arthrospira strains exhibited the highest activity, which in the case of Arthrospira S1 was approximately twofold higher in comparison to those in nitrogen-fixing strains. In addition to this, statistical analysis has indicated that detected phenolics were not major contributor to antioxidant capacities of tested cyanobacteria. However, this study highlights cyanobacteria of the genera Nostoc, Anabaena, and Arthrospira as producers of antioxidants and phenolics with pharmacological and health-beneficial effects, i.e., quinic acid and catechin in particular.     

Toxicity and bioaccumulation of iron in soil microalgae

Microalgae are extensively used in the remediation of heavy metals like iron. However, factors like toxicity, bioavailability and iron speciation play a major role in its removal by microalgae. Thus, in this study, toxicity of three different iron salts (FeSO₄, FeCl₃ and Fe(NO₃)₃) was evaluated towards three soil microalgal isolates, Chlorella sp. MM3, Chlamydomonas sp. MM7 and Chlorococcum sp. MM11. Interestingly, all the three iron salts gave different EC50 concentrations; however, ferric nitrate was found to be significantly more toxic followed by ferrous sulphate and ferric chloride. The EC₅₀ analysis revealed that Chlorella sp. was significantly resistant to iron compared to other microalgae. However, almost 900 μg g^?1 iron was accumulated by Chlamydomonas sp. grown with 12 mg L^?1 ferric nitrate as an iron source when compared to other algae and iron salts. The time-course bioaccumulation confirmed that all the three microalgae adsorb the ferric salts such as ferric nitrate and ferric chloride more rapidly than ferrous salt, whereas intracellular accumulation was found to be rapid for ferrous salts. However, the amount of iron accumulated or adsorbed by algae, irrespective of species, from ferrous sulphate medium is comparatively lower than ferric chloride and ferric nitrate medium. The Fourier transform infrared spectroscopy (FTIR) analysis shows that the oxygen atom and P?=?O group of polysaccharides present in the cell wall of algae played a major role in the bioaccumulation of iron ions by algae.     

Photoautotrophic Production of Lipids by Some <Emphasis Type="Italic">Chlorella</Emphasis> Strains

The microalgae Chlorella protothecoides UTEX 25, Chlorella sp. TISTR 8991, and Chlorella sp. TISTR 8990 were compared for use in the production of biomass and lipids under photoautotrophic conditions. Chlorella sp. TISTR 8990 was shown to be potentially suitable for lipid production at 30°C in a culture medium that contained only inorganic salts. For Chlorella sp. TISTR 8990 in optimal conditions in a stirred tank photobioreactor, the lipid productivity was 2.3 mg L⁻¹ h⁻¹ and after 14 days the biomass contained more than 30% lipids by dry weight. To attain this, the nitrogen was provided as KNO₃ at an initial concentration of 2.05 g L⁻¹ and chelated ferric iron was added at a concentration of 1.2 × 10⁻⁵ mol L⁻¹ on the ninth day. Under the same conditions in culture tubes (36 mm outer diameter), the biomass productivity was 2.8-fold greater than in the photobioreactor (0.125 m in diameter), but the lipid productivity was only 1.2-fold higher. Thus, the average low-light level in the photobioreactor actually increased the biomass specific lipid production compared to the culture tubes. A light-limited growth model closely agreed with the experimental profiles of biomass production, nitrogen consumption, and lipid production in the photobioreactor.     

Investigation of simultaneous lutein and lipid extraction from wet microalgae using Nile Red as solvatochromic shift probe

Microalgae have been proposed as an alternative lutein source due to their high productivity, reliability, and versatility. In this study lutein and lipid extraction from wet Chlorella vulgaris UTEX 265 was investigated. The lutein production was monitored throughout the microalgal growth phase and several extraction parameters such as the sample size, drying method, and cell disruption method were investigated. The performance of solvents on lutein extraction was compared using Nile Red as a solvatochromic polarity probe. The simultaneous lutein and lipid extraction was also studied for different polarities using an ethanol-hexane binary solvent at the optimal solvent compositions suitable for lutein extraction. Among the solvents investigated, 3:1 (v/v) ethanol/hexane was recognized as the optimal solvent for lutein and lipid co-extraction, which contributed to a 13.03 mg g^?1 lutein and 101.8 mg g^?1 FAME yield. The saponifiable lipids content (86.9% w/w) was higher than conventional extraction methods. Based on our results, wet extraction approach exhibits good potential, while the bead-beater is the most suitable technique for cell disruption and lutein extraction.