Synthesis of proposed structure of ledebourin A.

Naturally occurring homoisoflavonoids have attracted significant attention in the field of medicinal chemistry due to their potential health benefits and diverse range of biological properties. Recently, C-prenylated homoisoflavonoids, namely ledebourin A, B, and C, were isolated from the bulbs of Ledebouria floribunda and have exhibited potent antioxidant activity. In this study, we successfully synthesized ledebourin A and its regioisomer, compounds 1 and 9. By comparing the NMR spectra of the synthesized compounds with those of reported ledebourin A, we observed discrepancies. Nonetheless, our synthesis and subsequent findings offer valuable insights into the structural revision and biological activities of these unique prenylated homoisoflavonoids. Both synthesized compounds 1 and 9 exhibited no toxicity towards Hep-G2 cells and displayed the ability to recover glyceraldehyde-induced cell death, suggesting their potential as protective agents against liver damage.

Biodiesel production potential of microalgae, cultivated in acid mine drainage and livestock wastewater.

The adaptability and biofuel production potential of two strains of microalgae isolated and cultivated in livestock wastewater effluent (LWE) with acid mine drainage (AMD) were investigated. The isolated strains of microalgae from samples obtained from LWE and AMD, two microalgal strains (Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17) were selected based on their growth rate and lipid productivity. The dry cell weight of Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17 after 20 days of cultivation in AMD increased from 0.05 to 0.59 g/L and from 0.05 to 0.55 g/L, respectively. These findings revealed a significant accumulation of fatty acids with increasing AMD content. Nephroselmis sp. KGE2 in LWE with 5% AMD demonstrated a higher growth rate (0.59 ± 0.03 g/L) and fatty acid production (401.5 ± 47.3 mg/L) than Autodesmus obliquus KGE17 with 5% AMD. Additionally, Nephroselmis sp. KGE2 had C16-C18 fatty acid content (92.4%) in LWE with AMD. Biodiesel produced from Nephroselmis sp. KGE2 had a higher cetane number (52.31) and iodine value (88.26 g I2/100 g oil). Consequently, Nephroselmis sp. KGE2 can be considered a potential candidate for biodiesel production using AMD as an iron source.

High-throughput integrated pretreatment strategies to convert high-solid loading microalgae into high-concentration biofuels.

The commercial feasibility of energy-efficient conversion of highly concentrated microalgal suspensions to produce high-titer biofuels is a major bottleneck due to high energy consumption. Herein, high-titer biofuels (bioethanol, higher-alcohols, and biodiesel) were generated from carbohydrate-rich Chlamydomonas mexicana and lipid-rich Chlamydomonas pitschmannii biomass through energy-saving microwave pretreatment, successive fermentation, and transesterification. Microwave pretreatment needed low specific energy (4.2 MJ/kg) for 100 g/L of microalgal suspension. Proposed sustainable integrated pretreatments method achieved unprecedented total conversion efficiency (67%) and highest biomass utilization (87%) of C. pitschmannii (100 g/L) with high yields of bioethanol (0.48 g-ethanol/g-carbohydrates), higher-alcohols (0.44 g-higher-alcohols/g-proteins), and biodiesel (0.90 g-biodiesel/g-lipids). Transmission electron microscopy showed the changes in the microalgal cellular integrity before and after sequential fermentations. Energy-efficient integrated pretreatments enhanced the extraction efficiency and whole utilization of high-concentration microalgae to generate high-titer biofuels with minimum waste production.

Metabolic pathways for microalgal biohydrogen production: Current progress and future prospectives.

Microalgal biohydrogen (bioH2) has attracted global interest owing to its potential carbon-free source of sustainable renewable energy. Most of previous reviews which focused on microalgal bioH2, have shown unclear differentiation among the metabolic pathways. In this review, investigation of all different metabolic pathways for microalgal bioH2 production along with discussion on the recent research work of last 5-years have been considered. The major factors (such as light, vital nutrients, microalgal cell density, and substrate bioavailability) are highlighted. Moreover, effect of various pretreatment approaches on the constituent's bioaccessibility is reported. Microbial electrolysis cells as a new strategy for bioH2 production is stated. Comparison between the operation conditions of various bioreactors and economic feasibility is also emphasized. Genetic, metabolic engineering, and synthetic biology as recent technologies improved the microalgal bioH2 production through inactivation of uptake hydrogenase (H2ase), inhibition of the competing pathways in polysaccharide synthesis, and improving the O2 tolerant H2ase.

Heavy metal speciation with prediction model for heavy metal mobility and risk assessment in mine-affected soils.

Heavy metals from mines affect the soil and groundwater, and cause and severely impact on the health of local residents. The soil samples were characterized for the distribution and by the chemical speciation method, and then estimated the human health risks of the two mineaffected soils after stabilization process.. Two extraction techniques (Tessier and Wenzel methods) were applied to fractionate metals, such as arsenic (As) and zinc (Zn), to quantify the chemical status of metals in the soils. The mobility of As and Zn was predicted using the ASTM test and sequential extraction (Tessier and Wenzel) method results. The correlation coefficients of As and Zn mobility prediction using Tessier and Wenzel Fraction 1 were 0.920 and 0.815, respectively. The sum of fractions F1 + F2 + F3 showed the highest correlation coefficients value and F value for mobility prediction of both As and Zn. The hazardous indices (HI) for non-carcinogenic risk and carcinogenic risk (CR) to humans were evaluated according to the pseudo-total concentrations of metal in soils. The CR values of carcinogenic for As were within the ranges from 1.38 × 10-4 to 1.25 × 10-3 and 3.71 × 10-4 to 3.35 × 10-3 for both Young Dong (YD) and Dea San (DS), respectively. The HI for non-carcinogenic risk was the highest for As in the YD (2.77) and DS (7.46) soils, which covered approximately 96 and 84% of HI, respectively. In summary, the contribution of As to risk from heavy metals was dominant.

Effect of flue gas CO2 on the growth, carbohydrate and fatty acid composition of a green microalga Scenedesmus obliquus for biofuel production.

Effect of various flue gas CO2 concentrations (5%, 10% and 14.1%) on growth rate and biochemical properties of a green microalga Scenedesmus obliquus was investigated. S. obliquus showed the highest biomass production and growth rate (0.36 g L-1 and µmax = 1.00 day-1), total inorganic carbon removal (35.8 mg L-1), lipid productivity (9.9 mg L-1 day) and carbohydrate productivity (10.3 mg L-1 day) with 14.1% CO2 after 8 days of cultivation. Fatty acid methyl ester analysis revealed that the palmitic and oleic acid contents were increased up to 5% and 7% with 14.1% CO2, respectively. Application of flue gas CO2 enhanced the growth along with lipid and carbohydrate productivity of S. obliquus, which can be exploited for reducing the CO2 concentration.

Microalga, Acutodesmus obliquus KGE 30 as a potential candidate for CO2 mitigation and biodiesel production.

In this study, the effect of flue gas CO2 on growth, lipid production, and fatty acid composition of a green microalga Acutodesmus obliquus KGE 30 was investigated. The highest growth rate (0.46 g L(-1) and µmax = 1.09 day(-1)), total inorganic carbon removal (95.9 mg L(-1)), and lipid productivity (20.1 mg L(-1) day L(-1)) was obtained at 14.1 % CO2 after 4 days of cultivation. In a semicontinuous batch reactor, the highest biomass production (1.19 g L(-1)) was achieved after 12 days with continuous injection of flue gas CO2. Compared with synthetic CO2, fatty acid methyl ester analysis showed that the amount of unsaturated fatty acid increased by 19.2 % with 14.1 % flue gas CO2. The application of flue gas CO2 improved biomass production and lipid productivity in A. obliquus. The current investigation demonstrated that the use of flue gas CO2 could reduce the cost of microalgae biomass production for better biofuel generation.

Biodegradation of carbamazepine using freshwater microalgae Chlamydomonas mexicana and Scenedesmus obliquus and the determination of its metabolic fate.

This study evaluated the toxicity and cellular stresses of carbamazepine (CBZ) on Chlamydomonas mexicana and Scenedesmus obliquus, and its biodegradation by both microalgal species. The growth of both microalgal species decreased with increase of CBZ concentration. The growth of S. obliquus was significantly inhibited (97%) at 200 mg CBZ L(-1), as compared to the control after 10days; whereas, C. mexicana showed 30% inhibition at the same experimental conditions. Biochemical characteristics including total chlorophyll, carotenoid contents and enzyme activities (SOD and CAT) for both species were affected by CBZ at relatively high concentration. C. mexicana and S. obliquus could achieve a maximum of 35% and 28% biodegradation of CBZ, respectively. Two metabolites (10,11-dihydro-10,11-expoxycarbamazepine and n-hydroxy-CBZ) were identified by UPLC-MS, as a result of CBZ biodegradation by C. mexicana. This study demonstrated that C. mexicana was more tolerant to CBZ and could be used for treatment of CBZ contaminated wastewater.

Biosorption of Cu(II) by immobilized microalgae using silica: kinetic, equilibrium, and thermodynamic study.

Immobilized microalgae using silica (IMS) from Micractinium reisseri KGE33 was synthesized through a sol-gel reaction. Green algal waste biomass, the residue of M. reisseri KGE33 after oil extraction, was used as the biomaterial. The adsorption of Cu(II) on IMS was tested in batch experiments with varying algal doses, pH, contact times, initial Cu(II) concentrations, and temperatures. Three types of IMSs (IMS 14, 70, and 100) were synthesized according to different algal doses. The removal efficiency of Cu(II) in the aqueous phase was in the following order: IMS 14 (77.0%) < IMS 70 (83.3%) < IMS 100 (87.1%) at pH 5. The point of zero charge (PZC) value of IMS100 was 4.5, and the optimum pH for Cu(II) adsorption was 5. Equilibrium data were described using a Langmuir isotherm model. The Langmuir model maximum Cu(II) adsorption capacity (q m) increased with the algal dose in the following order: IMS 100 (1.710 mg g(-1)) > IMS 70 (1.548 mg g(-1)) > IMS 14 (1.282 mg g(-1)). The pseudo-second-order equation fitted the kinetics data well, and the value of the second-order rate constant increased with increasing algal dose. Gibbs free energies (ΔG°) were negative within the temperature range studied, which indicates that the adsorption process was spontaneous. The negative value of enthalpy (ΔH°) again indicates the exothermic nature of the adsorption process. In addition, SEM-energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses of the IMS surface reveal that the algal biomass on IMS is the main site for Cu(II) binding. This study shows that immobilized microalgae using silica, a synthesized biosorbent, can be used as a cost-effective sorbent for Cu(II) removal from the aqueous phase.

Mixotrophic cultivation of a microalga Scenedesmus obliquus in municipal wastewater supplemented with food wastewater and flue gas CO2 for biomass production.

The biomass and lipid/carbohydrate production by a green microalga Scenedesmus obliquus under mixotrophic condition using food wastewater and flue gas CO2 with municipal wastewater was investigated. Different dilution ratios (0.5-2%) of municipal wastewater with food wastewater were evaluated in the presence of 5, 10 and 14.1% CO2. The food wastewater (0.5-1%) with 10-14.1% CO2 supported the highest growth (0.42-0.44 g L(-1)), nutrient removal (21-22 mg TN L(-1)), lipid productivity (10-11 mg L(-1)day(-1)) and carbohydrate productivity (13-16 mg L(-1)day(-1)) by S. obliquus after 6 days of cultivation. Food wastewater increased the palmitic and oleic acid contents up to 8 and 6%, respectively. Thus, application of food wastewater and flue gas CO2 can be employed for enhancement of growth, lipid/carbohydrate productivity and wastewater treatment efficiency of S. obliquus under mixotrophic condition, which can lead to development of a cost effective strategy for microalgal biomass production.

As(III) and As(V) removal from the aqueous phase via adsorption onto acid mine drainage sludge (AMDS) alginate beads and goethite alginate beads.

Acid mine drainage sludge (AMDS) is a solid waste generated following the neutralization of acid mine drainage (AMD). This material entrapped in calcium alginate was investigated for the sorption of As(III) and As(V). Three different adsorbent materials were prepared: AMDS alginate beads (AABs), goethite alginate beads (GABs), and pure alginate beads. The effects of pH and the adsorption kinetics were investigated, and the adsorption isotherms were also evaluated. The optimum pH range using the AABs was determined to be within 2-10 for As(III) and 2-9 for As(V). Adsorption equilibrium data were evaluated using the Langmuir isotherm model, and the maximum adsorption capacity qmax was 18.25 and 4.97 mg g(-1) for As(III) on AAB and GAB, respectively, and 21.79 and 10.92 mg g(-1) for As(V) on AAB and GAB, respectively. The adsorption of As(III) and As(V) was observed to follow pseudo-second order kinetics. The As K-edge X-ray absorption near-edge structure (XANES) revealed that the adsorbed As(III) on the AABs was oxidized to As(V) via manganese oxide in the AMDS.

Application of acid mine drainage for coagulation/flocculation of microalgal biomass.

A novel application of acid mine drainage (AMD) for biomass recovery of two morphologically different microalgae species with respect to AMD dosage, microalgal cell density and pH of medium was investigated. Optimal flocculation of Scenedesmus obliquus and Chlorella vulgaris occurred with 10% dosage of AMD at an initial pH 9 for both 0.5 and 1.0 g/L cell density. The flocculation efficiency was 89% for S. obliquus and 93% for C. vulgaris. Zeta potential (ZP) was increased from -10.66 to 1.77 and -13.19 to 1.33 for S. obliquus and C. vulgaris, respectively. Scanning electron microscope with energy-dispersive X-ray of the microalgae floc confirmed the sweeping floc formation mechanism upon the addition of AMD. Application of AMD for the recovery of microalgae biomass is a cost-effective method, which might further allow reuse of flocculated medium for algal cultivation, thereby contributing to the economic production of biofuel from microalgal biomass.

Effect of food wastewater on biomass production by a green microalga Scenedesmus obliquus for bioenergy generation.

Effect of food wastewater (FW) on the biomass, lipid and carbohydrate production by a green microalga Scenedesmus obliquus cultivated in Bold's Basal Medium (BBM) was investigated. Different dilution ratios (0.5-10%) of BBM either with FW or salt solution (NaCl) or sea water (SW) were evaluated. S. obliquus showed the highest growth (0.41 g L(-1)), lipid productivity (13.3 mg L(-1) day L(-1)), carbohydrate productivity (14.7 mg L(-1) day L(-1)) and nutrient removal (38.9 mg TN L(-1) and 12.1 mg TP L(-1)) with 1% FW after 6 days of cultivation. The FW promoted algal autoflocculation due to formation of inorganic precipitates at an alkali pH. Fatty acid methyl ester analysis revealed that the palmitic and oleic acid contents were increased up to 8% with FW. Application of FW improved the growth, lipid/carbohydrate productivity and biomass recovery efficiency of S. obliquus, which can be exploited for cost effective production of microalgae biomass.

Enhancement of microalgae growth and fatty acid content under the influence of phytohormones.

The growth of Scenedesmus obliquus improved with increase in phytohormones concentrations (10(-8)-10(-)(5)M). Indole-3-acetic acid (IAA) supported the maximum growth at 10(-5)M with 17.7×10(6)cells/mL and total fatty acid of 97.9mg/g-DCW, enhancing the growth by 1.9-fold compared to control (9.5×10(6)cells/mL). While 10(-5)M of a newly discovered phytohormone Diethyl aminoethyl hexanoate (DAH) demonstrated a 2.5-fold higher growth with 23.5×10(6)cells/mL and a total fatty acid content of 100mg/g-DCW. Poly-unsaturated fatty acid content increased up to 56% and 59% at 10(-)(5)M of IAA and DAH, respectively. The highest carbohydrate content (33% and 34%) achieved at 10(-8)M and 10(-5)M of IAA and DAH, respectively. While, the highest protein content (34% and 35%) obtained at 10(-8)M of IAA and DAH, respectively. The current investigation demonstrates that phytohormones accelerate microalgal growth and induce the quality and quantity of fatty acid content for biodiesel production.

Toxicity of atrazine and its bioaccumulation and biodegradation in a green microalga, Chlamydomonas mexicana.

This study evaluated the toxicity of herbicide atrazine, along with its bioaccumulation and biodegradation in the green microalga Chlamydomonas mexicana. At low concentration (10 µg L(-1)), atrazine had no profound effect on the microalga, while higher concentrations (25, 50, and 100 µg L(-1)) imposed toxicity, leading to inhibition of cell growth and chlorophyll a accumulation by 22 %, 33 %, and 36 %, and 13 %, 24 %, and 27 %, respectively. Atrazine 96-h EC50 for C. mexicana was estimated to be 33 µg L(-1). Microalga showed a capability to accumulate atrazine in the cell and to biodegrade the cell-accumulated atrazine resulting in 14-36 % atrazine degradation at 10-100 µg L(-1). Increasing atrazine concentration decreased the total fatty acids (from 102 to 75 mg g(-1)) and increased the unsaturated fatty acid content in the microalga. Carbohydrate content increased gradually with the increase in atrazine concentration up to 15 %. This study shows that C. mexicana has the capability to degrade atrazine and can be employed for the remediation of atrazine-contaminated streams.

Isolation of novel microalgae from acid mine drainage and its potential application for biodiesel production.

Microalgae were selected and isolated from acid mine drainage in order to find microalgae species which could be cultivated in low pH condition. In the present investigation, 30 microalgae were isolated from ten locations of acid mine drainage in South Korea. Four microalgae were selected based on their growth rate, morphology, and identified as strains of KGE1, KGE3, KGE4, and KGE7. The dry biomass of microalgae species ranged between 1 and 2 g L(-1) after 21 days of cultivation. The growth kinetics of microalgae was well described by logistic growth model. Among these, KGE7 has the highest biomass production (2.05 ± 0.35 g L(-1)), lipid productivity (0.82 ± 0.14 g L(-1)), and C16-C18 fatty acid contents (97.6 %). These results suggest that Scenedesmus sp. KGE 7 can be utilized for biodiesel production based on its high biomass and lipid productivity.

Effect of mine wastewater on nutrient removal and lipid production by a green microalga Micratinium reisseri from concentrated municipal wastewater.

Effect of mine wastewater on the nutrient removal efficiency of a green microalga Micratinium reisseri from concentrated municipal wastewater (CMW) with simultaneous lipid production was investigated. Different dilution ratios (1-10%) of CMW either with mine wastewater (MWF) or mine wastewater without Fe (MWOF) were used. M. reisseri showed the highest growth (0.8gL(-1)) and nutrient uptake (35.9mgTNL(-1) and 5.4mgTPL(-1)) at 3% MWF ([Fe]tot=6.7mgL(-1)), and the highest lipid productivity (10.4mgL(-1)day(-1)) at 5% MWF ([Fe]tot=11.2mgL(-1)) after 15days. CMW supported the algal autoflocculation due to formation of phosphate, calcium and magnesium precipitates at a high suspension pH. Fatty acid methyl ester analysis revealed that the microalgal lipids possessed 79-82% of C16/C18 fatty acids. Application of mine wastewater improved the nutrient removal efficiency, growth and lipid productivity of M. reisseri cultivated in CMW.

Photoautotrophic hydrogen production by eukaryotic microalgae under aerobic conditions.

Eukaryotic algae and cyanobacteria produce hydrogen under anaerobic and limited aerobic conditions. Here we show that novel microalgal strains (Chlorella vulgaris YSL01 and YSL16) upregulate the expression of the hydrogenase gene (HYDA) and simultaneously produce hydrogen through photosynthesis, using CO2 as the sole source of carbon under aerobic conditions with continuous illumination. We employ dissolved oxygen regimes that represent natural aquatic conditions for microalgae. The experimental expression of HYDA and the specific activity of hydrogenase demonstrate that C. vulgaris YSL01 and YSL16 enzymatically produce hydrogen, even under atmospheric conditions, which was previously considered infeasible. Photoautotrophic H2 production has important implications for assessing ecological and algae-based photolysis.

Biomass, lipid content, and fatty acid composition of freshwater Chlamydomonas mexicana and Scenedesmus obliquus grown under salt stress.

Two freshwater microalgae including Chlamydomonas mexicana and Scenedesmus obliquus were grown on Bold Basal Medium (BBM) with different levels of salinity up to 100 mM NaCl. The dry biomass and lipid content of microalgae were improved as the concentration of NaCl increased from 0 to 25 mM. Highest dry weight (0.8 and 0.65 g/L) and lipid content (37 and 34 %) of C. mexicana and S. obliquus, respectively, were obtained in BBM amended with 25 mM NaCl. The fatty acid composition of the investigated species was also improved by the increased NaCl concentration. At 50 mM, NaCl palmitic acid (35 %) and linoleic acid (41 %) were the dominant fatty acids in C. mexicana, while oleic acid (41 %) and α-linolenic acid (20 %) were the major fractions found in S. obliquus.

Simultaneous nutrient removal and lipid production from pretreated piggery wastewater by Chlorella vulgaris YSW-04.

The feasibility of using a microalga Chlorella vulgaris YSW-04 was investigated for removal of nutrients from piggery wastewater effluent. The consequent lipid production by the microalga was also identified and quantitatively determined. The wastewater effluent was diluted to different concentrations ranging from 20 to 80 % of the original using either synthetic media or distilled water. The dilution effect on both lipid production and nutrient removal was evaluated, and growth rate of C. vulgaris was also monitored. Dilution of the wastewater effluent improved microalgal growth, lipid productivity, and nutrient removal. The growth rate of C. vulgaris was increased with decreased concentration of piggery wastewater in the culture media regardless of the diluent type. Lipid production was relatively higher when using synthetic media than using distilled water for dilution of wastewater. The composition of fatty acids accumulated in microalgal biomass was dependent upon both dilution ratio and diluent type. The microalga grown on a 20 % concentration of wastewater effluent diluted with distilled water was more promising for generating high-efficient biodiesel compared to the other culture conditions. The highest removal of inorganic nutrients was also achieved at the same dilution condition. Our results revealed the optimal pretreatment condition for the biodegradation of piggery wastewater with microalgae for subsequent production of high-efficient biodiesel.