Transcriptomic profile of lettuce seedlings (Lactuca sativa) response to microalgae extracts used as biostimulant agents

To reduce the use of chemical fertilizers and maximize agricultural yields, the use of microalgae extracts as biostimulants has recently attracted significant attention due to their favourable impact on both plant growth and their ability to induce tolerance towards environmental stressors. Lettuce (Lactuca sativa) is one of the most important fresh vegetables that often requires applications of chemical fertilizers to increase quality and productivity. Accordingly, the purpose of this study was to analyse the transcriptome reprogramming of lettuce (L. sativa) seedlings in response to either Chlorella vulgaris or Scenedesmus quadricauda extracts by applying an RNAseq approach. Differential gene expression analysis revealed that the core gene set that responded to microalgal treatments in a species-independent manner includes 1330 clusters, 1184 of which were down-regulated and 146 up-regulated, clearly suggesting that the repression of gene expression is the main effect of algal treatments. The deregulation of 7197 transcripts in the C. vulgaris treated seedlings compared to control samples (LsCv vs. LsCK) and 7118 transcripts in the S. quadricauda treated seedlings compared to control samples (LsSq vs. LsCK) were counted. Although the number of deregulated genes turned out to be similar between the algal treatments, the level of deregulation was higher in LsCv versus LsCK than in LsSq versus LsCK. In addition, 2439 deregulated transcripts were observed in the C. vulgaris treated seedlings compared to S. quadricauda treated samples (LsCv vs. LsSq comparison) suggesting that a specific transcriptomic profile was induced by the single algal extracts. 'Plant hormone signal transduction' category includes a very elevated number of DEGs, many of them specifically indicating that C. vulgaris actives both genes involved in the auxin biosynthesis and transduction pathways, whereas S. quadricauda up-regulates genes implicated in the cytokinin biosynthesis pathway. Finally, algal treatments induced the deregulation of genes encoding small hormone-like molecules that are known to act alone or by interacting with major plant hormones. In conclusion, this study offers the groundwork to draw up a list of putative gene targets with the aim of lettuce genetic improvement that will allow a limited or even null use of synthetic fertilizers and pesticides in the management of this crop.

Calcium sulfite oxidation activated by ferrous iron integrated with membrane filtration for removal of typical algal contaminants

Oxidation treatment of algae-laden water may cause cells rupture and emission of intracellular organics, thus restricting its further popularization. As a moderate oxidant, calcium sulfite could be slowly released in the liquid phase, thus exhibiting a potential to maintain the cells integrity. To this end, calcium sulfite oxidation activated by ferrous iron was proposed integrated with ultrafiltration (UF) for removal of Microcystis aeruginosa, Chlorella vulgaris and Scenedesmus quadricauda. The organic pollutants were significantly eliminated, and the repulsion between algal cells was obviously weakened. Through fluorescent components extraction and molecular weights distribution analyses, the degradation of fluorescent substances and the generation of micromolecular organics were verified. Moreover, the algal cells were dramatically agglomerated and formed larger flocs under the premise of maintaining high cell integrity. The terminal normalized flux was ascended from 0.048 to 0.072 to 0.711-0.956, and the fouling resistances were extraordinarily decreased. Due to the distinctive spiny structure and minimal electrostatic repulsion, Scenedesmus quadricauda was easier to form flocs, and its fouling was more readily mitigated. The fouling mechanism was remarkably altered through postponing the formation of cake filtration. The membrane interface characteristics including microstructures and functional groups firmly proved the fouling control efficiency. The reactive oxygen species (i.e., SO₄^•- and ¹O₂) generated through the principal reactions and Fe-Ca composite flocs played dominant roles in alleviating membrane fouling. Overall, the proposed pretreatment exhibits a brilliant application potential for enhancing UF in algal removal.

Effects of polystyrene nanoplastics on the physiological and biochemical characteristics of microalga Scenedesmusquadricauda

The contamination of the aquatic environment with microplastics has become a global environmental concern. Microplastic particles can be shredded to form smaller nanoplastics, and knowledge on their impacts on phytoplankton, especially freshwater microalgae, is still limited. To investigate this issue, the microalga Scenedesmus quadricauda was exposed to polystyrene nanoplastics (PS-NPs) of five concentrations (10, 25, 50, 100, and 200 mg/L). The growth; the contents of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD); the chlorophyll content; and concentrations of soluble protein and soluble polysaccharide were accordingly measured. The results showed that the microalgal density increased with the increase of the polystyrene nanoplastic concentrations, and the physiological features of alga were enhanced after the stimulation of nanoplastics. Furthermore, a high concentration (200 mg/L) of nanoplastics increased the contents of chlorophyll, soluble protein, and polysaccharide (P < 0.05). The antioxidant enzyme activities of Scenedesmus quadricauda were significantly activated by nanoplastics. Lastly, we propose three possible algal recovery mechanisms in response to nanoplastics in which Scenedesmus quadricauda was tolerant with PS-NPs by cell wall thickening, internalization, and aggregation. The results of this study contribute to understanding of the ecological risks of nanoplastics on freshwater microalgae.

Microalgae and Bacteria Interaction-Evidence for Division of Diligence in the Alga Microbiota

Microalgae are one of the most dominant forms of life on earth that is tightly associated with a distinct and specialized microbiota. We have previously shown that the microbiota of Scenedesmus quadricauda harbors less than 10 distinct microbial species. Here, we provide evidence that dominant species are affiliated with the genera of Variovorax, Porphyrobacter, and Dyadobacter. Experimental and transcriptome-based evidence implies that within this multispecies interaction, Dyadobacter is a key to alga growth and fitness and is highly adapted to live in the phycosphere. While presumably under light conditions the alga provides the energy source to the bacteria, Dyadobacter produces and releases mainly a large variety of polysaccharides modifying enzymes. This is coherent with high-level expression of the T9SS in alga cocultures. The transcriptome data further imply that quorum-quenching proteins (QQ) and biosynthesis of vitamins B1, B2, B5, B6, and B9 are expressed by Dyadobacter at high levels in comparison to Variovorax and Porphyrobacter. Notably, Dyadobacter produces a significant number of leucine-rich repeat (LRR) proteins and enzymes involved in bacterial reactive oxygen species (ROS) tolerance. Complementary to this, Variovorax expresses the genes of the biosynthesis of vitamins B2, B5, B6, B7, B9, and B12, and Porphyrobacter is specialized in the production of vitamins B2 and B6. Thus, the shared currency between partners are vitamins, microalgae growth-promoting substances, and dissolved carbon. This work significantly enlarges our knowledge on alga-bacteria interaction and demonstrates physiological investigations of microalgae and associated bacteria, using microscopy observations, photosynthetic activity measurements, and flow cytometry. IMPORTANCE The current study gives a detailed insight into mutualistic collaboration of microalgae and bacteria, including the involvement of competitive interplay between bacteria. We provide experimental evidence that Gram-negative bacteria belonging to the Dyadobacter, Porphyrobacter, and Variovorax are the key players in a Scenedesmus quadricauda alga-bacteria interaction. We impart strong evidence that Dyadobacter produces and releases polysaccharides degradation enzymes and leucine-rich repeat proteins; Variovorax supplies the consortium with auxins and vitamin B12, while Porphyrobacter produces a broad spectrum of B vitamins. We show not only that the microalgae collaborate with the bacteria and vice versa but also that the bacteria interact with each other via quorum-sensing and secretion system mechanisms. The shared currency between partners appears to be vitamins, microalgae growth-promoting substances, and dissolved carbon.

Effect of 17β-Estradiol on Growth and Biosynthesis of Microalgae Scenedesmus quadricauda (CPCC-158) and Duckweed Lemna minor (CPCC-490) Grown in Three Different Media

As fish farm wastewaters have detectable levels of fish hormones, such as 17β-estradiol (E2), an understanding of the influence of fish steroids on algal (Scenedesmus quadricauda) and duckweed (Lemna minor) physiology is relevant to the potential use of fishery wastewaters for microalgae and plant biomass production. The study was conducted using three types of media: Bold Basal Medium (BBM), natural fishery wastewater (FWW), and reconstituted fishery wastewater (RFWW) with the nutrient composition adjusted to mimic FWW. During the experiment, the media were aerated and changes in the pH and conductivity of the water were closely monitored. E2 promoted the growth of S. quadricauda and L. minor, with significant accumulation of high-value biomolecules at very low steroid concentrations. However, clear differences in growth performance were observed in both test cultures, S. quadricauda and L. minor, grown in different media, and the most effective hormone concentrations were evidently different for the algae and the plant.

Effect of complex iron on the phosphorus absorption by two freshwater algae

Iron plays an important role in physiological processes of microalgae and also affects the absorption of other nutrients by algae cells. Therefore, iron is one of the important controlling factors for algae bloom formation. This study investigated the effect of four kinds of complex iron (EDTA-Fe, ferric humate, ferric oxalate and ferric ammonium citrate) on the phosphorus absorption by two freshwater algae (Scenedesmus quadricauda and Anabaena flos-aquae). The results showed that the species and concentration of complex iron had a significant effect on the phosphorus uptake rate of S. quadricauda, but had only a slight effect on that of A. flos-aquae. The former exhibits positive influences on phosphorus absorption and was in the following order: ferric oxalate and EDTA-Fe > ferric humate and ammonium ferric citrate, and these effects depended on whether the presence of complex iron constitutes an environmental pressure for the growth of algal cells.

under optimized culture conditions

Microalgae are a potential source of a wide range of food and novel value-added products. The versatility of microalgae to produce different kind of pigments is gaining interest as a sustainable source of natural carotenoids. Currently, commercial production of carotenoids from selected microalgae requires special culture conditions which are difficult to maintain. The present study has been undertaken to optimize culture conditions for growth and carotenoid production by a new isolate Scenedesmus quadricauda PUMCC 4.1.40. The results revealed that test organism produced 1.54 mg dry biomass/ml with a content of 40 μg carotenoids/mg dry biomass during stationary phase. The growth and carotenoid production was increased by 2.4-fold under combined optimized culture conditions. The optimized conditions were growth medium, Chu-10; pH 8.5; temperature, 30°C; nitrogen, 20 mM nitrate; phosphate, 0.22 mM; NaCl, 0.42 mM and blue light. Separation and identification of four important carotenoids through high-performance thin-layer chromatography (HPTLC) followed by purification using flash chromatography and quantification by HPLC revealed 23.8, 19.0, 6.5, and 4.0 μg astaxanthin, β-carotene, lutein, and canthaxanthin /mg dry biomass, respectively. The amount of total carotenoids (98 μg/mg dry biomass) containing 40% valuable astaxanthin and β-carotene produced under optimized conditions was significantly higher than control cultures. This justifies that S. quadricauda is a promising candidate for scale-up production of carotenoid.

Toxicity assessments of acrylamide in aquatic environment using two algae Nitzschia closterium and Scenedesmus quadricauda

The expanding production and widespread application of acrylamide caused inevitable release to aquatic ecosystems. Contrary to its extensive attention to human and animal health, the hazards of acrylamide to the aquatic primary productivity have been rarely studied. The potential effects of acrylamide on the marine algae (Nitzschia closterium) and the limnetic algae (Scenedesmus quadricauda) were investigated by monitoring cell abundance, total chlorophyll content, maximum photosystem II (PSII) quantum yield (Fv/Fm), and reactive oxygen species (ROS). The growth of two algae was significantly inhibited by acrylamide. The 96 h EC₅₀ of acrylamide on N. closterium and S. quadricauda were 5.50 mg L^-1 and 45.3 mg L^-1, and no observed effect concentration (NOEC) were 1.07 mg L^-1 and 6.97 mg L^-1, respectively. After 96 h exposure to 50 mg L^-1 of acrylamide, the total chlorophyll content declined to approximate 18% (N. closterium) and 48% (S. quadricauda), and Fv/Fm was observed to be 0.35 and 0.32 for N. closterium and S. quadricauda, respectively. ROS was significantly increased following higher exposure concentrations, and its levels increased around 2.1-fold and 1.4-fold following exposure to 5 mg L^-1 of acrylamide. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the visible cell plasmolysis, rupture of the plasma membrane, cell vacuolization, and disintegration of chloroplasts of the algae caused acrylamide.

A study into the species sensitivity of green algae towards imidazolium-based ionic liquids using flow cytometry

The sensitivity of individual organisms towards toxic agents is an important indicator of environmental pollution. However, organism-specific quantification of sensitivity towards pollutants remains a challenge. In this study, we determined the sensitivity of Chlorella vulgaris (C. vulgaris) and Scenedesmus quadricauda (S. quadricauda) towards three ionic liquids (ILs), 1-alkyl-3-methyl-imidazolium chlorides [C_nmim][Cl] (n = 4,6,8). We kept all external parameters constant to identify the biotic parameters responsible for discrepancies in species sensitivity, and used flow cytometry to determine four conventional endpoints to characterise cell viability and cell vitality. Our results demonstrate that after exposure to the ILs, cell proliferation was inhibited in both species. At the same time, the cell size, complexity and membrane permeability of both algae also increased. However, while Chl a synthesis by S. quadricauda was inhibited, that of C. vulgaris was enhanced. S. quadricauda has evolved a metabolic defense that can counteract the decreased esterase activity that has been shown to occur in the presence of ILs. While it is likely that S. quadricauda was less sensitive than C. vulgaris to the ILs because of this metabolic defense, this alga may also exhibit better membrane resistance towards ILs.

Ecotoxicological effects of traffic-related pollutants in roadside soils of Moscow

The objective of this research is to find correlations between traffic-related contaminants in the roadside soils and their ecotoxicity. The study was conducted in Moscow in the vicinity of a highway of 125 000 vehicles per day. The topsoils (0-3 cm depth) were sampled perpendicular to the road at 1-, 6-, 10-, 18- and 50-m distances from the roadbed. Total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAH), heavy metals (HM) in total and phyto-available forms, and deicing salts (DS) were determined. A battery of soil-contacting organisms was tested: phytotoxicity of rye (H. vulgare L.) and garden cress (L. sativum L.); E. foetida earthworm growth rate and mortality; basal and substrate-induced respiration activity, nitrogen fixation and the denitrification activity of the soil microbial complex. To determine the possible risk to aquatic ecosystems, the algal toxicity test (S. quadricauda) was provided. Correlations between "chemical" data and intensity of "biological" effects were analyzed. Concentrations of most contaminants declined to the background values with distance from the road increase. However, the toxicity of roadside soils was obtained for all examined organisms within the whole 50 m zone. Live organisms exhibited different sensitivities to roadside soils pollution. The intensity of inhibition effects decreased in order: higher plants > earthworms and microorganisms > algae. The risk for aquatic ecosystems was assessed as low. Higher plants toxicity correlated with TPH, PAH, some HM, and DS; earthworm toxicity correlated with TPH, some PAH, HM, and DS; microorganism toxicity correlated with TPH and DS; algae had no observed correlations with contaminants. TPH and DS were general ecotoxicants affecting all organisms. Higher plants may be considered the PAH indicators and earthworms as HM indicators. A set of higher plants and earthworms may be recommended as the reduced test-battery of relevant organisms for cost-effective assessment of the toxicity of roadside soils.

Draft genome sequence and detailed characterization of biofuel production by oleaginous microalga Scenedesmus quadricauda LWG002611

BACKGROUND

Due to scarcity of fossil fuel, the importance of alternative energy sources is ever increasing. The oleaginous microalgae have demonstrated their potential as an alternative source of energy, but have not achieved commercialization owing to some biological and technical inefficiency. Modern methods of recombinant strain development for improved efficacy are suffering due to inadequate knowledge of genome and limited molecular tools available for their manipulation.

RESULTS

In the present study, microalga Scenedesmus quadricauda LWG002611 was selected as the preferred organism for lipid production as it contained high biomass (0.37 g L-1 day-1) and lipid (102 mg L-1 day-1), compared to other oleaginous algae examined in the present study as well as earlier reports. It possessed suitable biodiesel properties as per the range defined by the European biodiesel standard EN14214 and petro-diesel standard EN590:2013. To investigate the potential of S. quadricauda LWG002611 in details, the genome of the organism was assembled and annotated. This was the first genome sequencing and assembly of S. quadricauda, which predicted a genome size of 65.35 Mb with 13,514 genes identified by de novo and 16,739 genes identified by reference guided annotation. Comparative genomics revealed that it belongs to class Chlorophyceae and order Sphaeropleales. Further, small subunit ribosomal RNA gene (18S rRNA) sequencing was carried out to confirm its molecular identification. S. quadricauda LWG002611 exhibited higher number of genes related to major activities compared to other potential algae reported earlier with a total of 283 genes identified in lipid metabolism. Metabolic pathways were reconstructed and multiple gene homologs responsible for carbon fixation and triacylglycerol (TAG) biosynthesis pathway were identified to further improve this potential algal strain for biofuel production by metabolic engineering approaches.

CONCLUSION

Here we present the first draft genome sequence, genetic characterization and comparative evaluation of S. quadricauda LWG002611 which exhibit high biomass as well as high lipid productivity. The knowledge of genome sequence, reconstructed metabolic pathways and identification of rate-limiting steps in TAG biosynthesis pathway will strengthen the development of molecular tools towards further improving this potentially one of the major algal strains for biofuel production.

Higher biomolecules yield in phytoplankton under copper exposure

Copper is an important metal for industry, and its toxic threshold in natural ecosystems has increased since the industrial revolution. As an essential nutrient, it is required in minute amounts, being toxic in slightly increased concentrations, causing great biochemical transformation in microalgae. This study aimed at investigating the physiology of Scenedesmus quadricauda, a cosmopolitan species, exposed to copper concentrations including those that trigger intracellular biochemical modifications. The Cu exposure concentrations tested ranged from 0.1 to 25 µM, thus including environmentally important levels. Microalgae cultures were kept under controlled environmental conditions and monitored daily for cell density, in vivo chlorophyll a, and photosynthetic quantum yield (Φ_M). After 24 h growth, free Cu²⁺ ions were determined, and after 96 h, cellular Cu concentration, total carbohydrates, proteins, lipids, and cell volume were determined. The results showed that both free Cu²⁺ ions and cellular Cu increased with Cu increase in culture medium. Microalgae cell abundance and in vivo chlorophyll a were mostly affected at 2.5 µM Cu exposure (3.8 pg Cu cell^-1) and above. Approximately 31% decrease of photosynthetic quantum yield was obtained at the highest Cu exposure concentration (25 µM; 25 pg Cu cell^-1) in comparison with the control. However, at environmentally relevant copper concentrations (0.5 µM Cu; 0.4 pg Cu cell^-1) cell volume increased in comparison with the control. Considering biomolecules accumulation per unit cell volume, the highest carbohydrates and proteins yield was obtained at 1.0 µM Cu (1.1 pg Cu cell^-1), while for lipids higher Cu was necessary (2.5 µM Cu; 3.8 pg Cu cell^-1). This study is a contribution to the understanding of the effects of environmentally significant copper concentrations in the physiology of S. quadricauda, as well as to biotechnological approach to increase biomolecule yield in microalgae production.

The growth and lipid accumulation of Scenedesmus quadricauda during batch mixotrophic/heterotrophic cultivation using xylose as a carbon source

To overcome the bottlenecks of high cost and low production yields that restrict the commercial production of microalgae biodiesel, the use of xylose was evaluate by Scenedesmus quadricauda FACHB-1297, which was shown to be capable of mixotrophic and heterotrophic growth and lipid production on xylose, rich in the waste streams from pulp and paper industry, with increases in lipid productivities of 35.8-fold (mixotrophic) and 9.2-fold (heterotrophic) in comparison to photoautotrophic lipid yields. Five doses of xylose were tested to determine the effects and mechanisms of the carbon source on microalgae in mixotrophic mode. At the optimal xylose dosage of 4 g/L, the highest lipid content (38.61%) and productivity (139.55 mg/L/d) were achieved besides maximum biomass productivity (361.4 mg/L/d), nutrient removal efficiency of 68.4% (nitrogen), 97.2% (phosphorus) and 35.2% (xylose). Those indicated that S. quadricauda FACHB-1297 was suitable for further development of using xylose from certain waste streams for biofuel production.

Causes and mechanisms on the toxicity of layered double hydroxide (LDH) to green algae Scenedesmus quadricauda

Layered double hydroxides (LDHs) are widely used nanomaterials in industrial catalysis, pharmaceuticals, and environmental remediation, and may pose potential negative effects in the aquatic environment. However, little information is available on their toxicity to aquatic organisms. In this study, toxicity of LDH to a typical freshwater green algae Scenedesmus quadricauda was systematically investigated and the underlying mechanisms were elucidated. The growth of S. quadricauda was significantly inhibited by LDH at 72 h with a half maximal effective concentration (EC₅₀) and lowest observed effect concentration (LOEC) of 10.0 and 1.5 mg L^-1, respectively. Shading effect was observed, and the photosynthetic activity and cellular chlorophyll production were also severely suppressed by LDH. LDH also enhanced the reactive oxygen species production from S. quadricauda and lipid peroxidation in algal cells. Such algal toxicity of LDH might be mainly induced by the shading effect, agglomeration and physical interactions, and oxidative stress. The agglomeration and physical interactions contributed more to the algal toxicity at 72 h-EC₅₀ LDH concentrations. The results from the present study provided new insights and a better understanding of the environmental behavior and adverse effects of LDHs in the surface waters.

The growth of Scenedesmus quadricauda in RO concentrate and the impacts on refractory organic matter, Escherichia coli, and trace organic compounds

This study achieves a better operational simplicity for the phycoremediation of reverse osmosis (RO) concentrate using Scenedesmus quadricauda microalgae. Under continuous illumination with CO₂ supplementation, algal growth in the RO concentrate resulted in a conversion of polymeric organic matter (a mixture of humic substances and polysaccharides) to biodegradable fractions and their prompt removal along with inorganic nutrients (NO₃^- and PO₄^3-). The algal-induced degradation of humic-like substances which are typically refractory to microbial decomposition was demonstrated in an indirect manner. In this study, we also investigated the effects of algal treatment on the growth of Escherichia coli and removal of trace organic compounds (TOrCs) from the RO concentrate. Our results indicate that algal treatment of the RO concentrate using aeration with 10% (v/v) CO₂ under continuous illumination is highly feasible as a safe and inexpensive technology to remove non- or slowly-biodegradable organic matter, reduce enteric bacteria, and attenuate TOrCs in wastewater. However, the results should not be generalized, but critically discussed, due to limitations of using the synthetic RO concentrate in evaluating the performance of wastewater remediation with microalgae.

Cultivating Chlorella vulgaris and Scenedesmus quadricauda microalgae to degrade inorganic compounds and pesticides in water

This work evaluates the possibility of cultivating Scenedesmus quadricauda and Chlorella vulgaris microalgae in wastewater from the hydroponic cultivation of tomatoes with the aim of purifying the water. S. quadricauda and C. vulgaris were also used in purification tests carried out on water contaminated by the following active ingredients: metalaxyl, pyrimethanil, fenhexamid, iprodione, and triclopyr. Fifty-six days after the inoculum was placed, a reduction was found in the concentration of nitric nitrogen, ammonia nitrogen, and soluble and total phosphorus. The decrease was 99, 83, 94, and 94 %, respectively, for C. vulgaris and 99, 5, 88, and 89 %, respectively, for S. quadricauda. When the microalgae were present, all the agrochemicals tested were removed more quickly from the water than from the sterile control (BG11). The increase in the rate of degradation was in the order metalaxyl > fenhexamid > iprodione > triclopyr > pyrimethanil. It was demonstrated that there was a real degradation of fenhexamid, metalaxyl, triclopyr, and iprodione, while in the case of pyrimethanil, the active ingredient removed from the substrate was absorbed onto the cells of the microalgae. It was also found that the agrochemicals used in the tests had no significant effect on the growth of the two microalgae. The experiment highlighted the possibility of using cultivations of C. vulgaris and S. quadricauda as purification systems for agricultural wastewater which contains eutrophic inorganic compounds such as nitrates and phosphates and also different types of pesticides.

Influence of abscisic acid on growth, biomass and lipid yield of Scenedesmus quadricauda under nitrogen starved condition

Scenedesmus quadricauda, accumulated more lipid but with a drastic reduction in biomass yield during nitrogen starvation. Abscisic acid (ABA) being a stress responsible hormone, its effect on growth and biomass with sustainable lipid yield during nitrogen depletion was studied. The result revealed that the ABA level shoots up at 24h (27.21pmol/L) during the onset of nitrogen starvation followed by a sharp decline. The external supplemented ABA showed a positive effect on growth pattern (38×10(6)cells/ml) at a lower concentration. The dry biomass yield is also increasing up to 2.1 fold compared to nitrogen deficient S. quadricauda. The lipid content sustains in 1 and 2μM concentration of ABA under nitrogen-deficient condition. The fatty acid composition of ABA treated S. quadricauda cultures with respect to nitrogen-starved cells showed 11.17% increment in saturated fatty acid content, the desired lipid composition for biofuel application.

Enhanced lipid accumulation and biomass yield of Scenedesmus quadricauda under nitrogen starved condition

The experimental results revealed that the 2.27-fold lipid yield was enhanced in nitrogen-depleted condition (226 mg/L) when compared to nitrogen rich condition (99.33 mg/L). Since specific growth rate (SGR) is the single most criteria to decide the biomass yield of microalgae, SGR was analyzed. SGR of 0.33 day(-1) was observed with 0.47 doubling per day under nitrogen rich condition. However, low growth rate of 0.14 day(-1) with a doubling of 0.20 per day was recorded under nitrogen depleted condition. In accordance with SGR, the dry biomass yield was ranged from 0.055 ± 0.005 to 1.394 ± 0.010 g/L in the presence of nitrogen, indicating the essentiality of major nutrient in the growth medium. The enhanced lipid accumulation under nitrogen starved condition by Scenedesmus quadricauda was perhaps achieved by adopting adverse environmental condition and possible increment in cell size in terms of length/breadth ratio (1.11).

Biosorption and toxicity responses to arsenite (As[III]) in Scenedesmus quadricauda

Toxicity and biosorption responses to arsenite (As[III]) were examined in a 96-h exposure study using Scenedesmus quadricauda, one of the most popular green algae distributed in freshwaters in China. Results indicated that the pH-dependent distribution of two arsenite species (H2AsO3(-) and H3AsO3) played an important role in biosorption and toxicity. The undissociated H3AsO3 was more toxic than its monoanionic H2AsO3(-) through comparison of algal cell numbers, chlorophyll-a contents, and algal ultrastructural changes observed with transmission electron microscopy. An effective biosorption of 89.0mgg(-1) at 100mgL(-1) As[III] was found in the treatments with an initial pH of 9.3 and 25.2μgg(-1) at 0.03mgL(-1) As[III] at an initial pH of 8.2 as a result of the predominant species of H2AsO3(-) under the ambient pH and Eh conditions. Our results imply that S. quadricauda may provide a new means for the removal of toxic arsenite species present in contaminated surface water.