Effects of <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> extract on growth and antioxidant defense systems of two freshwater microalgae

Microalgae in genus Chlorella and Scenedesmus are common in aquatic ecosystems and are widely used for various studies on algal growth and applications. Macroalgae may play an important role for control of microalgal growth, attributable to their rich content of bioactive compounds. In this study, the brown seaweed Ascophyllum nodosum was extracted with 70% acetone and the extract was used to treat the green microalgae, Chlorella vulgaris and Scenedesmus sp. Cell density and chlorophyll a concentration were used as growth indexes to evaluate the effects of A. nodosum extract (ANE) on the microalgae. The ANE with concentrations > 1% exhibited significant capability of inhibition of the growth of microalgae by over 80%. On the contrary, 1% ANE caused varying degrees of acceleration of cell proliferation and chlorophyll a synthesis in C. vulgaris and Scenedesmus sp., respectively. Analysis of antioxidant activities of the enzymes superoxide dismutase (SOD) and catalase (CAT) revealed the impact of ANE on the antioxidant defense system of the microalgae. The SOD and CAT activities were significantly depressed by high concentrations (> 2%) ANE, while a slight increase of the enzyme activities was observed with 1% ANE at the early period, which could be correlated to the growth response. Therefore, the mechanism of microalgae control could be related to the interaction between the ANE and the antioxidant defense systems. Phlorotannins are proposed as the principal algistatic components in the ANE which could be utilized in controlling microalgae growth.     

Biotic Interactions between Two Species of Microalgae in Mixed Culture

Biotic interactions in a mixed culture of two microalgae species—Scenedesmus quadricauda (Turp.) Breb. and Monoraphidium arcuatum (Korsch.) Hind.—used in bioassay in monocultures as test objects were studied. The toxic effect of cell-free filtrates from different “age” monoculture (2, 7, 10, 15, 21, and 28 days) of S. quadricauda on the growth of the “young” test culture of M. arcuatum and, conversely, the toxic effect of cell-free filtrates from the different “age” (2, 7, 10, 15, 21, and 28 days) monoculture of M. arcuatum on the growth of the “young” test culture of S. quadricauda was evaluated. Simultaneously, the toxicity of their own filtrates of different “ages” was monitored by a test culture of each species. The interactions of the species in the mixed culture can be regarded as negative, as an antagonistic one, when both populations inhibit the growth of each other through metabolites and food resource competition, while the effect of S. quadricauda on M. arcuatum is much stronger. The main factor constraining the growth of monoculture S. quadricauda is the rapid depletion of the food resource from the medium and not the inhibition of growth by its own metabolites. The depletion of the food resources from the medium in monoculture of M. arcuatum occurs much later than in monoculture of S. quadricauda. Metabolites of S. quadricauda cause a strong inhibitory effect on the growth of M. arcuatum, and the metabolites of M. arcuatum cause a weak inhibitory effect on the growth of S. quadricauda. The filtrates of the “old” culture of S. quadricauda (21–28 days) cause the greatest inhibitory effect on cell division of M. arcuatum. The filtrates of the “old” culture of S. quadricauda (21–28 days) cause the greatest inhibitory effect on cell division of M. arcuatum. Comparative analysis of the cell number dynamics of two species, S. quadricauda and M. arcuatum, in mono- and two-species algal cultures, as well as experiments with filtrates of these monocultures, showed that the interaction of species can be explained by the food resource competition and allelopathic interaction (exometabolite effect).     

Consortium of Higher Aquatic Plants and Microalgae Designed to Purify Sewage of Heavy Metal Ions

We selected higher aquatic plants (HAP) and microalgae possessing a high sorption capacity in respect to heavy metals to form a consortium designed to purify contaminated aquatic ecosystems. Accumulation of heavy metals Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺ was investigated in plants Pistia stratiotes, Elodea canadensis, and Lemna minor and green microalgae Chlorella vulgaris ВВ-2, Ankistrodesmus sp. ВI-1, Chlamydomonas reinhardtii В-4, and Scеnеdеsmus quadricauda В-1. It was found that intense accumulation of metals occurs in cultures of HAP Pistia stratiotes and Elodea canadensis. These plants are macroconcentrators of zinc, lead, and copper and microconcentrators of cadmium. Out of the examined cultures of microalgae, effective bioaccumulators of heavy metals were C. vulgaris ВВ-2 and Ankistrodesmus sp. ВI-1. It was shown that heavy metals are selectively taken up from the medium in the series Zn²⁺ > Cu²⁺ > Cd²⁺ > Pb²⁺. In order to produce a consortium of higher aquatic plants and microalgae for purification of polluted aquatic ecosystems, we investigated interaction of HAP P. stratiotes and E. canadensis with microalgae C. vulgaris ВВ-2 and Ankistrodesmus sp. ВI-1 in the course of their cocultivation. Neutral relations were detected between the cells of microalgae C. vulgaris ВВ-2 and Ankistrodesmus sp. ВI-1 and HAP E. canadensis. At the same time, the cells of Ankistrodesmus sp. ВI-1 and HAP P. stratiotes formed a symbiosis. Microscopic examination showed numerous points where the cells of microalgae Ankistrodesmus sp. ВI-1 were attached to the roots of P. stratiotes plants. We tested an opportunity to employ the association between P. stratiotes and Ankistrodesmus sp. ВI-1 for purification of simulated wastewater polluted with heavy metal ions. This consortium proved to be capable of eliminating contaminants from the sewage, reducing their level in the sewage to standard values, and active accumulation of heavy metal ions.     

Microalgal Biomass and Lipid Production on Dairy Effluent Using a Novel Microalga, <Emphasis Type="Italic">Chlorella</Emphasis> sp. Isolated from Dairy Wastewater

The present study focused on cost-effective production of microalgal biomass and lipid production on dairy effluent. The novel microalga, Chlorella sp. isolated from the dairy effluent showed high growth and lipid production on the undiluted and two-fold diluted dairy effluent which were four to five times higher than those of Chlorella vulgaris (control). The high growth of Chlorella sp. was thought to be possibly due to its heterotrophic growth capacity, high turbidity, COD, nutrients and trace elements. In contrast, C. vulgaris showed poor heterotrophic and photoautotrophic growth under the highly turbid conditions of dairy effluent. Both Chlorella sp. and C. vulgaris showed similar total FAME (mg FAME/g algal cells). The fatty acid composition analysis revealed that both Chlorella sp. and C. vulgaris possessed major C18 and C20 fatty acids which will be used for biodiesel production. Overall, the novel microalga, Chlorella sp. isolated from the dairy effluent showed high potential for cost-effective algal cultivation and lipid production on dairy effluent without any modification of process.     

High biomass production and CO<Subscript>2</Subscript> fixation from biogas by <Emphasis Type="Italic">Chlorella</Emphasis> and <Emphasis Type="Italic">Scenedesmus</Emphasis> microalgae using tequila vinasses as culture medium

Tequila vinasses (TVs) generated during Tequila production are brown liquid residues rich in nutrients. The nutrient content of agro-industrial effluents represents an excellent resource to support low-cost biomass production of microalgae; nonetheless, it is crucial to select the suitable microalgal strain to attain the highest biomass production in each residue used. In this study, biomass production, CO₂ fixation from biogas, and cell compound accumulation by Chlorella vulgaris U162, Chlorella sp., Scenedesmus obliquus U169, and Scenedesmus sp. using biodigested and filtered TVs as culture medium were evaluated and compared with the conventional microalgal culture media, C30, BG-11, Bold 3N, and Bristol. The four microalgae evaluated attained the highest biomass production and CO₂ fixation rate cultured in both residues, accumulating mainly carbohydrates and proteins although the most appropriate microalga to be cultured in TVs was Chlorella sp., recording 2.30 g L^?1. Moreover, the nutrient ratio of filtered TVs was ideal to support biomass production while biodigested TVs need to be supplemented with nitrogen. Overall, these results demonstrated that tequila vinasses are an excellent resource to support high and quick biomass production of microalgae, which can be used to obtain biofuels as ethanol, biogas, and supplement food depicting an extra benefit during the appropriate disposal of this residue.     

Salinity tolerance of four freshwater microalgal species and the effects of salinity and nutrient limitation on biochemical profiles

Microalgae are ideal candidates for bioremediation and biotechnological applications. However, salinity and nutrient resource availability vary seasonally and between cultivation sites, potentially impacting on biomass productivity. The aim of this study was to screen pollutant-tolerant freshwater microalgae (Desmodesmus armatus, Mesotaenium sp., Scenedesmus quadricauda and Tetraedron sp.), isolated from Tarong power station ash-dam water, for their tolerance to cultivation at a range of salinities. To determine if biochemical composition could be manipulated, the effects of 4-day nutrient limitation were also determined. Microalgae were cultured at 2, 8, 11 and 18 ppt salinity, and nutrient uptake was monitored daily. Growth, total lipid, fatty acid (FA), and amino acid contents were quantified in biomass harvested while nutrient-replete and, after 4 days, nutrient-deplete. D. armatus showed the highest salinity tolerance actively growing in up to 18 ppt while Mesotaenium sp. was the least halotolerant with decreasing growth rates from 11 ppt. However, Mesotaenium sp. at 2 and 8 ppt had the highest biomass productivity and nutrient requirements of the four species, making it ideal for nutrient remediation of eutrophic freshwater effluents. Salinity and nutrient status had minimal influence on total lipid and FA contents in D. armatus and Mesotaenium sp., while nutrient depletion induced an increase of total lipid and FAs in S. quadricauda and Tetraedron sp., which was further increased with increasing salinity. As none of the growth conditions affected amino acid profiles of the species, these findings provide a basis for species selection based on site-specific salinity conditions and nutrient resource availability.     

Comparison of the culture and harvesting of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> and <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> for the removal of pharmaceuticals from water

The objective of this work was to assess and compare the removal efficiency of paracetamol and salicylic acid from aqueous medium by a microalgae-based treatment, using either Chlorella vulgaris or Tetradesmus obliquus. Moreover, considering microalgae application in wastewater treatment, the influence of these pharmaceuticals in the algal nutrient removal capacity was evaluated. The removal of paracetamol by T. obliquus (>40 %) was larger than by C. vulgaris (>21 %) in batch culture, and this was also observed for salicylic acid (>93 % by T. obliquus and >25 % by C. vulgaris). Both strains removed nutrients (phosphate and nitrate) almost completely by the end of the batch culture, but T. obliquus showed the highest efficiency at the steady state conditions of the semicontinuous culture. In spite of this, under the flocculants here tested, the efficiency in the recovery of biomass was much higher for C. vulgaris. These results highlight the importance of strain selection in the application of microalgae for wastewater treatment and, particularly, for the removal of pharmaceuticals.     

The eurythermal adaptivity and temperature tolerance of a newly isolated psychrotolerant Arctic <Emphasis Type="Italic">Chlorella</Emphasis> sp.

A new strain of Chlorella sp. (Chlorella-Arc), isolated from Arctic glacier melt water, was found to have high specific growth rates (μ) between 3 and 27 °C, with a maximum specific growth rate of 0.85 day^?1 at 15 °C, indicating that this strain was a eurythermal strain with a broad temperature tolerance range. To understand its acclimation strategies to low and high temperatures, the physiological and biochemical responses of the Chlorella-Arc to temperature were studied and compared with those of a temperate Chlorella pyrenoidosa strain (Chlorella-Temp). As indicated by declining F _v/F _m, photoinhibition occurred in Chlorella-Arc at low temperature. However, Chlorella-Arc reduced the size of the light-harvesting complex (LHC) to alleviate photoinhibition, as indicated by an increasing Chl a/b ratio with decreasing temperatures. Interestingly, Chlorella-Arc tended to secrete soluble sugar into the culture medium with increasing temperature, while its intracellular soluble sugar content did not vary with temperature changes, indicating that the algal cells might suffer from osmotic stress at high temperature, which could be adjusted by excretion of soluble sugar. Chlorella-Arc accumulated protein and lipids under lower temperatures (<15 °C), and its metabolism switched to synthesis of soluble sugar as temperatures rose. This reflects a flexible ability of Chlorella-Arc to regulate carbon and energy distribution when exposed to wide temperature shifts. More saturated fatty acids (SFA) in Chlorella-Arc than Chlorella-Temp also might serve as the energy source for growth in the cold and contribute to its cold tolerance.     

Comparison of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> and cyanobacterial biomass: cultivation in urban wastewater and methane production

Anaerobic digestion of microalgae is hampered by its complex cell wall. Against this background, cyanobacteria cell walls render this biomass as an ideal substrate for overcoming this drawback. The aim of the present study was to compare the growth of two cyanobacteria (Aphanizomenon ovalisporum and Anabaena planctonica) and a microalga (Chlorella vulgaris) in urban wastewater when varying the temperature (22, 27 and 32 °C). Cyanobacterial optimal growth for both strains was attained at 22 °C, while C. vulgaris did not show remarkable differences among temperatures. For all the microorganisms, ammonium removal was higher than phosphate. Biomass collected was subjected to anaerobic digestion. Methane yield of C. vulgaris was 184.8 mL CH₄ g COD in^?1 while with A. ovalisporum and A. planctonica the methane production was 1.2- and 1.4-fold higher. This study showed that cyanobacteria growth rates could be comparable to microalgae while presenting the additional benefit of an increased anaerobic digestibility.     

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

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

Reduced gene expression at the branch point of chlorophyll and heme biosynthesis in Arctic <Emphasis Type="Italic">Chlorella</Emphasis> ArM0029B

The gene expression at the branch point of chlorophyll and heme synthesis in the model microalga, Chlamydomonas reinhardtii, is different from that of higher plants. Another green alga, Arctic Chlorella, was recently isolated from Arctic sea ice and may be a promising candidate for a biofuel. To understand the chlorophyll metabolic pathway and relevant nuclear gene expression in Chlorella sp., we characterized chlorophyll-deficient mutants of the Arctic Chlorella sp. ArM0029B. First, we characterized the chlorophyll and heme biosynthetic pathways based on genes identified by bioinformatics analysis of the genome of Arctic Chlorella sp. ArM0029B. Then, we isolated and analyzed nine chlorophyll-deficient mutants that showed reduced expression of the ChlM gene, which encodes Mg-protoporphyrin methyltransferase. Expression of 5-amino levulinic acid dehydratase (encoded by ALAD) and glutamyl-tRNA reductase (encoded by HemA) was reduced in all nine independent mutants compared to wild type. These results indicated that Arctic Chlorella ArM0029B may have a regulatory mechanism of gene expression at earlier steps of the Mg-porphyrin branch that is more similar to higher plants than to the microalga C. reinhardtii. This study provides useful insight into the regulation of porphyrin precursor formation in Chlorella and related microalgae.     

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.     

Magnetophoretic harvesting of freshwater microalgae using polypyrrole/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite and its reusability

A magnetophoretic harvesting agent, a polypyrrole/Fe₃O₄ magnetic nanocomposite, is proposed as a cost and energy efficient alternative to recover biomass of the microalgae Botryococcus braunii, Chlorella protothecoides, and Chlorella vulgaris from their culture media. The maximal recovery efficiency reached almost 99 % for B. braunii, 92.4 % for C. protothecoides, and 90.8 % for C. vulgaris. The maximum adsorption capacity (Q ₀) of the magnetic nanocomposite for B. braunii (63.49 mg dry biomass mg^?1 PPy/Fe₃O₄) was higher than that for C. protothecoides (43.91 mg dry biomass mg^?1 PPy/Fe₃O₄) and C. vulgaris (39.98 mg dry biomass mg^?1 PPy/Fe₃O₄). The highest harvesting efficiency for all the studied microalgae were at pH 10.0, and measurement of zeta-potential confirmed that the flocculation was induced by charge neutralization. This study showed that polypyrrole/Fe₃O₄ can be a promising flocculant due to its high efficacy, low dose requirements, short settling time, its integrity with cells, and with great potential for saving energy because of its recyclability.     

Microalgal industry in China: challenges and prospects

Over the past 15 years, China has become the major producer of microalgal biomass in the world. Spirulina (Arthrospira) is the largest microalgal product by tonnage and value, followed by Chlorella, Dunaliella, and Haematococcus, the four main microalgae grown commercially. China’s production is estimated at about two-thirds of global microalgae biomass of which roughly 90 % is sold for human consumption as human nutritional products (‘nutraceuticals’), with smaller markets in animal feeds mainly for marine aquaculture. Research is also ongoing in China, as in the rest of the world, for other high-value as well as commodity microalgal products, from pharmaceuticals to biofuels and CO₂ capture and utilization. This paper briefly reviews the main challenges and potential solutions for expanding commercial microalgae production in China and the markets for microalgae products. The Chinese Microalgae Industry Alliance (CMIA), a network founded by Chinese microalgae researchers and commercial enterprises, supports this industry by promoting improved safety and quality standards, and advancement of technologies that can innovate and increase the markets for microalgal products. Microalgae are a growing source of human nutritional products and could become a future source of sustainable commodities, from foods and feeds, to, possibly, fuels and fertilizers.     

Oil production by six microalgae: impact of flocculants and drying on oil recovery from the biomass

Oil production in batch photoautotrophic cultures of the following microalgae is reported: the freshwater microalgae Chlorella vulgaris, Choricystis minor, and Neochloris sp.; the marine microalgae Nannochloropsis salina and Cylindrotheca fusiformis; and C. vulgaris grown in a full-strength seawater medium. In all cases, the solvent extraction of lipids from freeze-dried biomass is compared with extraction from the fresh biomass paste. For all algae, the oils could be extracted equally effectively from freeze-dried samples and the paste samples (67–88 % moisture by weight). Moisture content determinations of the biomass using the freeze-drying method and the high-temperature oven drying were found to be equivalent for all algae. The biomass recovered by flocculation with metal salts (aluminum sulfate, ferric chloride) followed by centrifugation had a certain amount of the flocculant irreversibly bound to it. Washing failed to remove the adsorbed flocculants. For all algae, the adsorbed flocculants did not interfere with oil recovery by solvent extraction. The solvent system of chloroform–methanol–water proved highly effective for quantitative extraction of the lipids from all algae.     

Effects of pH,Salinity, Biomass Concentration,and Algal Organic Matter on Flocculant Efficiency of Synthetic Versus Natural Polymers for Harvesting Microalgae Biomass

This study investigated the effects of pH, salinity, biomass concentration, and algal organic matter (AOM) on the efficiency of four commercial cationic flocculants. The tannin-based biopolymers Tanfloc SG and SL and the polyacrylamide polymers Flopam FO 4800 SH and FO 4990 SH were tested for flocculation of two microalgae models, the freshwater Chlorella vulgaris and the marine Nannochloropsis oculata. Both biomass concentration and AOM presence affected all polymers evaluated, whereas salinity and pH affected only Flopam and Tanfloc, respectively. A restabilization effect due to overdosing was only observed for Flopam polymers and increasing Tanfloc dose resulted in improved efficiency. Flopam polymers showed a significant decrease in the maximum quantum yield of photosystem II as function of polymer dose for Chlorella, which supported the need for toxicological studies to assess the potential toxicity of Flopam. In overall, Tanfloc was not affected by salinity nor presented potential toxicity therefore being recommended for the flocculation of both freshwater and marine species.     

Antioxidant responses of microalgal species to pyrene

The antioxidant response of four freshwater microalgal species, Chlorella vulgaris Beij., Scenedesmus platydiscus (G. M. Smith) Chod., Scenedesmus quadricauda(Turp.) Bréb., and Selenastrum capricornutum Printz without pyrene addition (control) and at two pyrene concentrations (0.1 and 1.0 mgL⁻¹) were investigated. Under the control condition, the values of the antioxidant parameters differed significantly among species and the difference was seemed not to be related to their susceptibility to pyrene. The antioxidant response to pyrene treatments also varied from species to species. Pyrene led to a significant increase in total glutathione (GSH) content in all species except C. vulgaris, a species did not exhibit any ability to metabolize pyrene. The glutathione-S-transferase (GST) activities also remained unchanged in pyrene treated C. vulgaris, increased greatly in S. platydiscus and Se. capricornutum (the two species with higher pyrene metabolism ability), but inhibited remarkably in S. quadricauda (the only species sensitive to pyrene toxicity). On the other hand, the glutathione reductase (GR) activities increased in C. vulgaris but remained at a similar level as the control in the other three species. The malondialdehyde (MDA) content, an indicator of lipid peroxidation, declined in S. quadricauda but showed no significant change in the other three species. The activities of glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) in pyrene treated cells remained almost the same as the controls for all microalgal species. Results suggested that the alterations of antioxidant systems in microalgae might not be useful indicators of pyrene exposure but pyrene-enhanced GSH metabolism might be important in pyrene biotransformation.     

An alternative strategy for enhancing lipid accumulation in chlorophycean microalgae for biodiesel production

Oleaginous microalgae are considered as important feedstocks for production of biodiesel. Under nutrient stress conditions, microalgae have the ability to accumulate higher amount of lipids, which can be transesterified for the production of biodiesel. In the present investigation, four different phosphate application strategies were examined in five green microalgae (Tetradesmus obliquus, Tetradesmus lagerheimii, Chlorella vulgaris, Chlorella minutissima, and Chlamydomonas sp.) to achieve higher lipid productivity. Effects of those strategies such as phosphate-sufficient (Control), phosphate-starved approach (PSA), biphasic phosphate-starved approach (BPSA), and sequential phosphate addition (SPA) were studied under batch culture mode. The BPSA emerging as the best in terms of lipid productivity consisted of two biomass harvesting phases, which would lead to an increase in the overall cost of biodiesel production. On the other hand, the SPA with a 1/200th dose of N 11 medium, i.e., 0.4 mg L^?1 of phosphate application in 3-day intervals, also resulted into higher lipid productivity which was equal to BPSA. Fatty acid composition of the biodiesel obtained from the microalgae was analyzed and the fuel characteristics were also evaluated. A profound (~14-fold) reduction in phosphorus requirements under the SPA mode with higher lipid productivity ensured qualitative biodiesel production and a lesser amount of phosphorus release, thus making the process eco-friendly.     

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

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

Bioaccessibility of phenolic compounds,lutein, and bioelements of preparations containing <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> in artificial digestive juices

Chlorella vulgaris Beijerinck is a spherical, green alga belonging to the genus Chlorella and family Chlorellaceae. It has high nutritional value and shows multiple biological effects. Dietary supplements that contain extracts of C. vulgaris are sold in the form of tablets, capsules, powders, and aqueous solutions. To the best of our knowledge, this is the first study to determine the content of bioelements (zinc, iron, and magnesium), phenolic compounds, and lutein before and after incubation with artificial digestive juices from preparations containing C. vulgaris. In this study, we used commercial preparations in the form of powder and tablets. The samples were incubated in artificial gastric juice and then in artificial intestinal juice for 30 and 90 min. The contents of bioelements were determined by using the flame atomic absorption spectrometric method. Lutein and phenolic compounds were analyzed by high-pressure liquid chromatography. We also aimed to evaluate the quality of chlorella-containing formulations by using the methods described in the European Pharmacopoeia 8th edition. According to the results, the preparations containing C. vulgaris demonstrated the presence of phenolic compounds and lutein. Therefore, daily supplementation of preparations containing C. vulgaris substantiates its usefulness for humans. The qualitative composition of the examined organic substances and bioelements was found to be in accordance with the manufacturer’s declarations on the packaging containing C. vulgaris compared with the control samples; however, the contents of bioelements were found to be negligible after incubation with artificial digestive juices. This shows that the examined preparations containing C. vulgaris are not good sources of bioelements such as zinc, iron, or magnesium.