Scenedesmus Obliquus Research Articles

Effects of Dissolved Organic Matter Fractions of Varying Molecular Weights and Cd2 + on Scenedesmus obliquus Growth

Effects of Dissolved Organic Matter Fractions of Varying Molecular Weights and Cd2 + on Scenedesmus obliquus Growth

Hazard assessment and environmental fate of propiconazole degradation by microalgae: Differential tolerance, antioxidant and detoxification pathway

Propiconazole (PCZ), a triazole broad spectrum fungicide has been frequently detected in agricultural water webs. This emerging contaminant imposes a serious toxic impact on soil and aquatic microbiota. Thus, we aimed to investigate the potential of the microalgae as PCZ phycoremediator. To this end, its toxicity, degradation and detoxification mechanisms by Scenedesmus obliquus and Nostoc muscorum were studied. Over a week, both species were exposed to mild (5 mg/L) and high (10 mg/L) PCZ concentrations. Results showed a dose-dependent accumulation of PCZ typically higher in S. obliquus than in N. muscorum. Moreover, S. obliquus degraded PCZ into a less toxic environmental product; 1-[2-(2,4-dichlorophenyl)− 4-(hydroxypropyl)− 1,3-dioxolan-2ylmethyl]− 1,2,4-triazole and 1-(2,4-dichlorophenyl)− 2-(1,2,4-triazol-1-yl) ethanone. The metabolic pathway assumed cellular dehydroxylation and side chain breakdown in S. obliquus. The high PCZ dose significantly decreased cell growth, chlorophyll a content and inhibited photosynthesis activity and machinery (PEPC and RuBisCo) in both species but, to lesser extend in S. obliquus. Additionally, the exposure to high concentration of PCZ caused a serious oxidative damage especially in N. muscorum. This damage is evident by increased lipid peroxidation, H2O2 level, protein oxidation and NADPH oxidase activity. The two species experienced differential antioxidant and detoxification mechanisms using glutathione-S-transferases, phytochelatins and metalothionine to alleviate PCZ-oxidative stress. This study represented S. obliquus as an efficient PCZ phycoremediator and provided new data on the PCZ toxicity, environmental fate and risk of PCZ to aquatic environment.

Effects of Nitrogen and Phosphorus Concentrations on the Growth and Lipid Accumulation of Microalgae Scenedesmus obliquus

In the study, Scenedesmus obliquus green algae was cultivated under laboratory conditions at 21±2°C, 16:8 (light:dark) photoperiod and continuous aeration in different nitrogen and phosphorus ratio nutrient medium and its growth was determined. Dry weight, cell density (optical density) and chlorophyll a and b were used to determine the growth of the algae. The best growth was determined in the group consisting of 30 ml NaNO3+10 ml PO4. The amount of biomass obtained was determined as 1.549 gL-1 in this group. The lowest values were the group containing 5 ml NaNO3+5 ml PO4. With the decrease in the amount of nitrogen in the medium, an increase in the amount of carotene and a decrease in the amount of chl a and b were detected. The highest lipid values were determined as 36.7% in the group containing 5 ml NaNO3+5 ml PO4 and 36.2% in the group containing 5 ml NaNO3+10 ml PO4.

Catalytic hydrothermal liquefaction of nutrient-stressed microalgae for production of high-quality bio-oil over Zr-doped HZSM-5 catalyst

The Hydrothermal liquefaction (HTL) of a nutrient-stressed microalgae (Scenedesmus obliquus) (NSM) with and without the use of zirconium-doped HZSM-5 catalyst was investigated under temperature conditions ranging from 250 to 350 °C. The wet impregnation method was used to prepare the catalyst, and HTL experiments were conducted on the unstressed microalgae (CM) for comparison. Under the stressed condition, the protein content of the microalgae was reduced from 42.35% to 22.08% while the carbohydrate and lipid contents were increased from 25.36% to 42.55% and 17.16%–21.62% respectively. The maximum HTL bio-oil yield of 52.8 wt% and 24.27 wt% were found for NSM and CM respectively at 350 °C with addition of Zr-HZSM-5 catalyst. Higher denitrogenation and deoxygenation was achieved with NSM compared to CM. At high temperature of 350 °C, the most abundant fatty acid in NSM was found to be cis-vaccenic acid (omega-7- fatty acid), and this could be explored for the possibility of extracting products of great value from the bio-oil for applications other than biofuels. Mainly, the use of Zr-doped HZSM-5 catalyst on nutrient-stressed S. obliquus microalgae resulted in enhanced bio-oil yield and characteristics which compared well with petroleum crude.

Cytotoxic Effect of a Novel GaFe2O4@Ag Nanocomposite Synthesized by Scenedesmus obliquus on Gastric Cancer Cell Line and Evaluation of BAX, Bcl-2 and CASP8 Genes Expression

Cytotoxic Effect of a Novel GaFe2O4@Ag Nanocomposite Synthesized by Scenedesmus obliquus on Gastric Cancer Cell Line and Evaluation of BAX, Bcl-2 and CASP8 Genes Expression

Invasive and toxic cyanobacteria regulate allochthonous resource use and community niche width of reservoir zooplankton

Abstract Cyanobacterial dominance or blooms can influence ecosystem structure in reservoirs, yet there are only few studies of its effect on the resource use and trophic structure of zooplankton. We hypothesised that zooplankton traits would exhibit a strong response to the increase of invasive and toxic cyanobacteria. We investigated the effect of an invasive bloom‐forming cyanobacterium Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii) on zooplankton functional traits (e.g., growth, reproduction, allochthonous resource use and realised niche) through laboratory experiments and 3‐year field investigations in two subtropical reservoirs. The realised niche (i.e., resource and habitat use) was quantified using stable isotopes (termed isotopic niches). We fed the cladoceran zooplankton Moina sp. with Scenedesmus obliquus (chlorophyte), R. raciborskii, and a mixture of S. obliquus and R. raciborskii in laboratory experiments. A diet of R. raciborskii alone depressed the growth and reproduction of Moina sp. compared to a diet of S. obliquus alone, but a mixture of S. obliquus and R. raciborskii greatly alleviated the inhibition effects caused by cyanobacteria. Under natural field conditions, we did not find a strong inhibition effect of R. raciborskii dominance on the zooplankton, but a high biomass of R. raciborskii was associated with an increase (17%) in the relative allochthonous resource (terrestrially derived organic matter) use by cladocerans (but not for copepods), even though the chlorophyll‐a concentration increased from 17 μg/L in the non‐bloom period to 28 μg/L during periods of R. raciborskii dominance or blooms. Furthermore, a high biomass of R. raciborskii increased the contribution of inter‐taxa variation (taxa sorting) to the expanded isotopic niches of the zooplankton community. Our study helps to clarify cyanobacteria‐zooplankton interactions and highlights the importance of cyanobacterial dominance or blooms in regulating cross‐ecosystem resource use and biogeochemical cycling mediated by zooplankton in aquatic ecosystems.

Antifungal properties of aqueous microalgal extracts

Microalgae are considered a promising source of eco-friendly antifungal agents that can potentially reduce the usage of synthetic fungicides. Hence, properties of aqueous extracts from Nannochloropsis sp., Phaeodactylum tricornutum, Scenedesmus obliquus, Chlorella vulgaris and Spirulina sp. were investigated in vitro regarding their antagonistic activity towards the phytopathogenic fungi Sclerotium rolfsii, Rhizoctonia solani, Botrytis cinerea and Alternaria alternata. S. obliquus showed the highest antifungal activity of all microalgal strains against Sclerotium rolfsii, inhibiting growth up to 32.01 ± 4.82%. Nannochloropsis sp. mitigated Sclerotium rolfsii by up to 13.96 ± 5.26%, while P. tricornutum suppressed the mycelial growth of Sclerotium rolfsii and Rhizoctonia solani by up to 18.35 ± 3.45%. Moreover, P. tricornutum and S. obliquus inhibited Botrytis cinerea growth by up to 11.47 ± 2.06%. The obtained results indicate that microalgae with fungicidal activity could replace chemical agents in modern and sustainable agricultural food production.

Enhancing biomass and lipid yield of microalga Scenedesmus obliquus by the periodic direct current

Nowadays, the disposal of municipal wastewater by microalgae while extracting microalgal high-value by-products has become an emerging trend. In this research, direct current electrochemical treatment was used to improve microalgae biomass production and wastewater treatment effect simultaneously. After electrochemical treatment, the cell number, biomass, chlorophyll-a content and lipid content of Scenedesmus obliquus cultivated in BG11 medium were significantly increased respectively by 13.1%, 32%, 9.7% and 30.1% at the 1.0 A/m2 direct current density. When Scenedesmus obliquus was cultured in real wastewater with electrochemical treatment at the 2.0 A/m2 direct current density, the biomass and lipid yield increased by 30.1% and 23.5%, respectively, while the removal of TP, ammonia and TN was also obviously accelerated. Therefore, the electrochemical cultivation of Scenedesmus obliquus offers good prospects for wastewater treatment and resource recycling.

Enhancing harvest of biodiesel-promising microalgae using Daphnia domesticated by amino acids

Mass production of microalgal biodiesel is hindered by microalgae harvesting efficiency and costs. In this study, Daphnia domesticated by amino acids were used to harvest microalgae via ingesting. The main factors (density of Daphnia, salinity, pH, light-environment, temperature and algal concentration) that were conducive to Daphnia feeding were optimized. Under the optimal condition, Microalgae-feeding Daphnia were domesticated by adding D-glutamic acid and L-cysteine as stimulating factors. After that, the ingestion rate of domesticated Daphnia increased by 24.93%. The presence of Daphnia as a predator can induce microalgae to mass into clusters. Combining Daphnia feeding and the inductive defense flocculation of microalgae, the harvesting rate of mixed algae (Chlorella pyrenoidosa and Scenedesmus obliquus) reached over 95% after 9 h. Overall, this work suggested that Daphnia feeding process is a green and economical approach for microalgae harvesting.

Enhancement performance of CO2 on the organic toxicity removal of sludge by Scenedesmus obliquus with proteomics analysis

Microalgae have strong adaptability to toxic environments. The accumulation of toxic organic matter and secondary metabolites during the biologically treatment of wastewater can cause sludge toxicity. Scenedesmus obliquus was cultivated in the sludge extract from coal-gasification synthetic wastewater contained 100 mg/L hydroquinone, with 15% CO2, to investigate the removal of sludge toxicity together with CO2 fixation. Results showed that S. obliquus could utilize the organic matter and CO2 in the mixed cultivation mode. On the 30th day, the dry cell weight was 1.46 ± 0.07 g/L, and chlorophyll-a was 24.76 ± 0.21 mg/L. S. obliquus reduced the sludge toxicity by heterotrophically utilizing the organic matter of sludge extract. TOC decreased from 393.52 ± 0.65 mg/L to 113.78 ± 0.43 mg/L, and organic matter with molecular weights of < 500 Da and 500–5KDa was significantly consumed, reducing the sludge toxicity from 83.46 ± 0.27% to 29.37 ± 0.19% in terms of inhibition rate of luminescent bacteria. S. obliquus mainly utilized HCO3- for autotrophic growth and the CO2 removal (%) was up to the maximum 35.08 ± 0.19% on the 10th day. Proteomics analysis results showed that 15% CO2 improved autotrophic ability of S. obliquus and the activity of the functional protein, thereby improving its antioxidant capacity against toxicity stress. By increasing its protein kinase and ATPase activity, S. obliquus enhanced the oxidative phosphorylation process to heterotrophically utilize organic matter to reduce the sludge toxicity.

K Value: An Indicator that can Characterize the Cold and Hot Properties of Traditional Chinese Medicines.

Aims: The cold and hot properties of Chinese medicines are an important concept to represent the function of drugs, and are also a unique classification method of traditional Chinese medicine (TCM). The method reflects an herb’s therapeutic properties and guides reasonable clinical prescription. However, the present key problem is the lack of an objective and quantitative evaluation index for the cold and hot properties of Chinese herbs. Delayed luminescence (DL) is the long-term afterglow of biological systems after illumination with light, which can reflect differences in herbal materials prepared under different conditions. We aim to use S. obliquus as an indicator organism to characterize the differences between the cold and hot properties of Chinese herbs. Methods: Scenedesmus obliquus (S. obliquus) was used as an indicator organism to characterize the differences between the cold and hot properties of Chinese herbs. The decoction solution of different properties of Chinese herbs was added to S. obliquus culture medium; then, the delayed luminescence (DL) of S. obliquus after the addition of decoctions of different properties of Chinese herbs was measured to obtain information on the effect of different properties of Chinese herbs on S. obliquus. Many DL parameters were calculated, and ROC curve analysis was applied with the aim of finding a suitable parameter that can characterize the differences in cold and hot properties of Chinese herbs. Results: Our results show that the K value is a sensitive parameter that can reflect the differences of cold and hot properties of Chinese herbs, thus providing new insights into the cold and hot properties of Chinese herbs. Conclusions: DL measurement of S. obliquus after addition of different properties of Chinese herbs could be a novel and promising method to study the cold and hot properties of Chinese herbs.

Application of global sensitivity analysis in identification of herbicides cocktail effects at environment-related concentrations

<p indent="0mm">The use of herbicides in crop production continues to increase globally. By 2015, China had become one of the most important producers and consumers of herbicides in the world. Many herbicides are persistent organic pollutants and are used continuously for long periods of time, causing the high residual concentrations in the water surrounding farmland and negative effects on aquatic life. The concentrations of herbicides in the environmental water are variable and the types of herbicides are diverse. Herbicide mixtures in surface water may threaten aquatic life. However, in most areas of China, the hazard of herbicide mixtures associated with environmental exposure levels has not been assessed. This paper establishes a hazard identification assessment method for mixtures with environment-related concentrations. Firstly, the hazard of individual pollutant was assessed by hazard quotient (HQ), and the pollutants with high hazards (HQ≥1) to target organisms were further studied. Secondly, the global sensitivity analysis (GSA) based on Morris method was used to study combined effect, and identify the important or hidden drivers in chemical mixtures. In brief, the GSA experimental design consists of four steps: Input factors (target pollutants), Morris sampling, high-throughput screening, and the sensitivity analysis. Thirty-nine herbicides detected in the surface water of Tai Lake and Liao River were screened by HQ with <italic>Scenedesmus obliquus</italic> (<italic>S</italic>.<italic> obliquus</italic>) individually. The herbicides with high hazard were the input factors of GSA. Then, the Morris method was used to generate 150 samples of mixtures. The <italic>S</italic>.<italic> obliquus </italic>was exposed to 150 samples for <sc>24 h</sc> and subjected to high-throughput screening. Finally, the sensitivity analysis was used to identify the important or hidden drivers of the herbicide mixtures. The results showed that 14 herbicides had high hazards (HQ≥1) among 39 herbicides detected in Tai Lake and Liao River basin. Ametryn and diflufenican had higher hazards to algae. At the individual herbicide exposure of <sc>500 μg/L,</sc> most herbicides, except C5 and C10, significantly inhibited the growth of <italic>S</italic>.<italic> obliquus </italic>(<italic>P</italic>&lt;0.05). And the strongest growth inhibition effect caused by individual herbicide was about 40%. The results of 150 samples of mixtures with environment-related concentration showed that most of the mixtures had growth inhibition effects on <italic>S</italic>.<italic> obliquus</italic>. The total concentrations of the mixtures that consist of 14 herbicides are not greater than <sc>79 μg/L.</sc> And the strongest growth inhibition effect caused by mixture samples was over 50%. The toxicity of herbicide mixtures cannot be ignored. The growth inhibition effect of the mixtures that consist of 14 herbicides on <italic>S</italic>.<italic> obliquus</italic> was nonlinear, and there are strong interactions between herbicides. It is difficult to predict the toxic effects of the mixture system from the exposure concentration of individual herbicides. According to the <italic>μ*</italic> value, the most important factors in the combined pollution were terbutryne, bensulfuron methyl, atrazine, and ametryn. Bentazone had the lowest <italic>μ*</italic> and contributed little to the overall mixture system. And bensulfuron methyl was the hidden driver of the mixture system. The important drivers in the herbicide mixtures need to be focused, and their concentrations should be monitored regularly to control emissions and minimize the negative effect on aquatic life. Global sensitivity analysis based on Morris sampling can identify the important factors in cocktail effects of mixtures in limited samples, providing technical support for incorporating the actual toxic effects of mixtures into the risk assessment of pollutants.

Photosynthetic Toxicity of Enrofloxacin on Scenedesmus obliquus in an Aquatic Environment.

Aquaculture facilities are a potential source of antibiotics in aquatic environments, having adverse effects on the algae species. In this study, the toxicity induced by enrofloxacin (ENR) on the algae Scenedesmus obliquus was evaluated. The uptake of ENR and the change in the growth and photosynthesis of algae were analyzed. At the exposure doses of 10–300 μg/L, the accumulated levels of ENR in algae were 10.61–18.22 μg/g and 12.09–18.34 μg/g after 48 h and 96 h of treatment, respectively. ENR inhibited the growth of algae, with a concentration for 50% effect of 119.74 μg/L, 53.09 μg/L, 64.37 μg/L, and 52.64 μg/L after 24 h, 48 h, 72 h and 96 h of treatment, respectively, indicating the self-protection and repair ability of algae in a short period of time. Furthermore, the chlorophyll contents decreased in all treatment groups, and the photosynthetic system Ⅱ parameters decreased in a dose-dependent manner under ENR stress, suggesting that ENR caused a disorder in the electron transport of the photosynthesis of algae, and the carbon fixation and assimilation processes were thus damaged. These results indicate that ENR poses a considerable risk to aquatic environments, affects the carbon sinks, and even has an adverse effect on human health.

Statistical optimization for simultaneous removal of methyl red and production of fatty acid methyl\xa0esters using fresh alga Scenedesmus obliquus

Microalgae are a diverse group of microorganisms, the majority of which are photosynthetic in nature. Microalgae have different applications, the most important of which is the biological treatment of wastewater. Microalgae grow in various types of wastewater, such as wastewater polluted by Azo dyes, due to microalgae using wastewater as a culture medium, which contains many nutrients like nitrogen, phosphate, and carbon sources. Microalgae grow in various types of wastewater, such as wastewater polluted by Azo dyes, due to microalgae using wastewater as a culture medium, which contains many nutrients like nitrogen, phosphate, and carbon sources. So, microalgae are used for bioremediation of wastewater due to the efficiency of growing in wastewater and for the high production of lipids followed by trans-esterification to biodiesel. Face-centered central composite design (FCCCD) was used to determine the factors that have the most significant impact on the simultaneous decolorization of methyl red and lipid production by the fresh green alga Scenedesmus obliquus. The predicted results indicated that the alga decolorized 70.15% methyl red and produced 20.91% lipids by using 1 g/L nitrogen, an incubation time of 10 days, a pH of 8, and the concentration of methyl red is 17.65 mg/L. The dry biomasses of S. obliquus were also examined by SEM and FTIR before and after treatment with methyl red. SEM and FTIR showed that the properties of dry S. obliquus were altered after the biosorption of methyl red. According to GC–MS analysis of hexane extracts of S. obliquus, the lipid profile differed before and after methyl red decolorization. The results proved that it is possible to use S. obliquus to remove dyes and produce renewable fuels such as biodiesel. The novelty of this study is that this is the first time in which the effect of nitrogen concentrations in the medium used for algal growth on the removal of dye has been studied.

Active indole-3-acetic acid biosynthesis by the bacterium Azospirillum brasilense cultured under a biogas atmosphere enables its beneficial association with microalgae.

This study assessed, at the physiological and molecular levels, the effect of biogas on indole-3-acetic acid (IAA) biosynthesis by Azospirillum brasilense as well as the impact of this bacterium during CO2 fixation from biogas by Chlorella vulgaris and Scenedesmus obliquus. IpdC gene expression, IAA production and the growth of A. brasilense cultured under air (control) and biogas (treatment) were evaluated. The results demonstrated that A. brasilense had a better growth capacity and IAA production (105.7±10.3μgml-1 ) when cultured under biogas composed of 25% CO2 +75% methane (CH4 ) with respect to the control (72.4±7.9μgml-1 ), although the ipdC gene expression level was low under the stressful condition generated by biogas. Moreover, this bacterium was able to induce a higher cell density and CO2 fixation rate from biogas by C. vulgaris (0.27±0.08gl-1 d-1 ) and S. obliquus (0.22±0.08gl-1 d-1 ). This study demonstrated that A. brasilense has the capacity to grow and actively maintain its main microalgal growth-promoting mechanism when cultured under biogas and positively influence CO2 fixation from the biogas of C. vulgaris and S. obliquus. These findings broaden research in the field of Azospirillum-microalga interactions and the prevalence of Azospirillum in environmental and ecological topics in addition to supporting the uses of plant growth-promoting bacteria to enhance biotechnological strategies for biogas upgrading.

Radish (Raphanus sativus L.) leaves: A novel source for a highly efficient heterogeneous base catalyst for biodiesel production using waste soybean cooking oil and Scenedesmus obliquus oil

In this study, a novel heterogeneous catalyst from the unexploited radish leaves (Raphanus sativus L.) was synthesized and employed for biodiesel production using waste soybean cooking oil (SWCO) and Scenedesmus obliquus oil (OSO). The synthesized catalyst (CLP) was characterized by FTIR, BET, XRD, TGA, SEM, TEM, EDX, BET, and XPS. Moreover, the Hammett indicator test and CO2-TPD were used to assess the derived catalyst's basicity. The results reported the presence of Ca, S, Si, Cl, Al, P, Mg, Mn, Na, and a high percentage of potassium (57.30 wt%) in the form of carbonates and oxides. The maximum SWCO and OSO conversion of 98.0% and 91.32% were obtained using 6 wt% and 5 wt% catalyst loading and 12:1, 16:1 methanol to oil molar ratio for 150 and 90 min at 60 °C, respectively. The CLP exhibits excellent recyclability, achieving 90.57% oil conversion after four successive cycles. The fuel properties of the produced biodiesel were compatible with international standards. The synthesized catalyst is highly efficient, cheap, renewable, green, and can help reduce biodiesel production costs. Thus, the CLP catalyst might be a promising candidate for large-scale biodiesel production with a competitive price.

The effects of aeration and mixotrophy by acetate and pyruvate on the growth parameters in Scenedesmus obliquus

The effects of aeration and mixotrophy by acetate and pyruvate on the growth parameters in Scenedesmus obliquus

OPTIMIZATION STUDIES FOR MICROALGAL GROWTH AND CAROTENOID PRODUCTION (BEFORE STRESS)

The demand for carotenoids in the global market is rising due to the high rate of degenerative diseases which have their origin from deleterious free radicals. Carotenoids are antioxidant molecules identified as the potential inhibitors of free radicles. Particularly, Microalgae carotenoids have drawn great attention, ‘due to their high photosynthetic efficiency, lack of land requirement, and ease of scale-up’. Presently, an attempt was made to optimize the primary growth of three microalgae (i.e., Chlorella vulgaris, Microcystis aeruginosa and Scenedesmus obliquus) prior to second fermentation for the production of carotenoids. Response surface methodology (RSM) was used to optimize experimental runs in an orbital shaker (Winpact SI-200, USA) in a controlled setting of pH and temperature. Growth of microalgae was measured as optical density (OD) as well as the total carotenoids (before stress) at the stationary growth stage. Optimum growth of Microalgae was achieved at a range of 250C -300C and pH 8-9 in all the Microalgae. High carotenoids (before stress) was 4.411mg/ml in Scenedesmus obliquus among others; however, this cannot be translated as the highest as carotenoids are optimized during stress.

Plasma-induced conversion of polystyrene nanoplastics in water: Intermediates release, toxicity, and disinfection byproducts formation

Widely distributed nanoplastics have become a threat to water environment. Information regarding their conversion behaviors and risks under oxidation conditions is still lacking. In this study, conversion of polystyrene nanoplastics (PSNPs) in water induced by electrical plasma was investigated, and its risks were evaluated in terms of Scenedesmus obliquus growth, Human alveolar cell A549 toxicity, and chlorinated disinfection byproducts (DBPs) formation. Attacks of 1O2 and ·OH resulted in rough surface, smaller particle size of PSNPs (particles larger than 200 nm disappeared, and it was in the range of 50–150 nm), sequence breakages in functional groups, and generation of hydroxylated and carboxylated intermediates. The plasma-treated PSNPs exhibited slightly weaker toxicity for Scenedesmus obliquus growth when PSNPs concentration was 30 mg L−1, but stronger toxicity for A549 (relative viability of A549 decreased from approximately 40% to 6.9% after 15 min treatment). The hydroxylated and carboxylated intermediates were important precursors of DBPs, and the formation potentials and toxicities of haloacetic acid DBPs increased with the plasma treatment. The relevant roadmaps among haloacetic acid DBPs and conversion intermediates were figured out. Overall, the conversion of PSNPs under oxidation exposure may pose a greater threat to DBPs formation, which deserved more attention.

Effect of nitrogen and carbon sources and salt stress on the bioactive components concentration in Scenedesmus obliquus

In Scenedesmus obliquus culture, the effects of different nitrogen and carbon sources and saline stress on total carotenoids, total proteins and total phenols contents were investigated. Microalgae in Allen &amp; Arnon culture medium were cultivated, until reaching the stationary phase. Then, sodium nitrate or urea as nitrogen source and sodium acetate or glucose as carbon source, were incorporated. Additionally, sodium chloride was added for cause saline stress. Fourteen treatments were carried out, during 40 days. Differences in bioactive components concentration were observed for the different nitrogen and carbon sources from day 26. When 0.24 g/L of urea were used, 3 times more of total carotenoids were obtained than when sodium nitrate was used; while, with 3.68 g/L of glucose, 1.5 times more of total carotenoids were reached than with sodium acetate was used. Total proteins concentration was 1.9 times higher when 0.24 g/L of urea and 5.02 g/L of sodium acetate were utilized as nitrogen and carbon sources, respectively. With 31.00 g/L of urea 4 times more of total phenols were obtained than with sodium nitrate; while, 12 times more of total phenols were achieved with 3.68 g/L of glucose than with sodium acetate. Saline stress caused a reduction in the bioactive components of interest. The highest concentrations obtained were: 513.20±13.21mg β-carotene/gdwc, 7.25±0.34 mg BSA/gdwc, and 16.78±0.54 mg GAE/gdwc. Therefore, this study confirmed that Scenedesmus obliquus microalgae developed strategies to adapt to the new conditions caused by the nitrogen and carbon sources incorporation, causing changes in the concentration of bioactive components.