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Heavy metal pollution in the cold region is serious, affecting human health and aquatic ecology. This study investigated the ability of microalgae to remove heavy metals (HMs) and produce lipid at low temperature. The removal efficiency of different HMs (Cd 2+ , Cu 2+ , Cr 3+ and Pb 2+ ), cell growth and lipid synthesis of microalgae were analyzed at 15 °C. Moreover, addition of glycine betaine (GB) further enhanced the productivity of microalgae in treating HMs and lipid production, and simultaneously increased the antioxidant capacity of microalgae against environmental stresses. The results showed that the highest lipid productivity of 100.98 mg L -1 d -1 and the removal efficiency of 85.8 % were obtained under GB coupled with Cr 3+ . The highest glutathione content of 670.34 nmol g -1 fresh alga was achieved under GB coupled with Pb 2+ . In addition, lipidomics showed that GB was able to up-regulate the triglyceride and diglyceride content, influenced fatty acid composition to regulate the microalgal metabolism, and mediated lipid accumulation under 15 °C mainly through the regulation of glycerol ester metabolism. This study provided a new perspective on microalgal lipid production and the removal of HMs in cold regions and provided evidence for the use of phytohormones to improve the algal environmental resistance., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The aim of this study was to investigate the effects of various concentrations of antioxidants, including butyl hydroxy anisd (BHA), butylated hydroxytoluene (BHT), fulvic acid (FA), melatonin (MT), glycine betaine (GB) and putrescine (Put), on growth and lipid synthesis of microalgae under low-temperature (15 ℃). Changes in biochemical indicators, reactive oxygen species (ROS) level, glutathione (GSH) content and antioxidant enzyme activities were also studied. The results indicated that the maximum biomass concentration (1.3 g/L) and lipid productivity (75.3 ± 5.8 mg/L d -1 ) were achieved under 100 μM MT and 1 μM GB, respectively. Moreover, antioxidants were able to increase the GSH and antioxidant enzymes activities in algal cells under low-temperature stress. This study was enlightening for the utilization of antioxidants to improve the resistance to low-temperature stress and lipid production in microalgae, and provided a theoretical basis for the application of microalgae for lipid accumulation in cold regions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Waste activated sludge (WAS) as one of the major pollutants with a significant annual production, has garnered significant attention regarding its treatment and utilization. If improperly discharged, it not only caused environmental pollution but also led to the wastage of valuable resources. In this study, the microalgae growth and lipid accumulation using waste activated sludge extracts (WASE) under different temperature conditions were investigated. The highest lipid content (59.13%) and lipid productivity (80.41 mg L -1 d -1 ) were obtained at cultivation temperatures of 10 and 25 °C, respectively. It was found that microalgae can effectively utilize TN/TP/NH 4 + -N were achieved at a cultivation temperature of 10 °C, reaching 84.97, 77.49 and 92.32%, respectively. The algal fatty acids had carbon chains predominantly ranging from C14 to C18, making them suitable for biodiesel production. Additionally, a comprehensive analysis of transcriptomics and metabolomics revealed up-regulation of genes associated with triglyceride assembly, the antioxidant system of algal cells, and cellular autophagy, as well as the accumulation of metabolites related to the tricarboxylic acid (TCA) cycle and lipids. This study offers novel insights into the microscopic mechanisms of microalgae culture using WASE and approaches for the resource utilization of sludge.4 + -N were achieved at a cultivation temperature of 10 °C, reaching 84.97, 77.49 and 92.32%, respectively. The algal fatty acids had carbon chains predominantly ranging from C14 to C18, making them suitable for biodiesel production. Additionally, a comprehensive analysis of transcriptomics and metabolomics revealed up-regulation of genes associated with triglyceride assembly, the antioxidant system of algal cells, and cellular autophagy, as well as the accumulation of metabolites related to the tricarboxylic acid (TCA) cycle and lipids. This study offers novel insights into the microscopic mechanisms of microalgae culture using WASE and approaches for the resource utilization of sludge., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

A coupling technology for lipid production and adsorption of rare earth elements (REEs) using microalgae was studied in this work. The microalgae cell growth, lipid production, biochemical parameters and lipid profiles were investigated under different REEs (Ce 3+ , Gd 3+ and La 3+ ). The results showed that the maximum lipid production was achieved at different concentrations of REEs, with lipid productivities of 300.44, 386.84 and 292.19 mg L -1 d -1 under treatment conditions of 100 μg L -1 Ce 3+ , 250 μg L -1 Gd 3+ and 1 mg L -1 La 3+ , respectively. Moreover, the adsorption efficiency of Ce 3+ , Gd 3+ and La 3+ exceeded 96.58 %, 93.06 % and 91.3 % at concentrations of 25-1000 μg L -1 , 100-500 μg L -1 and 0.25-1 mg L -1 , respectively. In addition, algal cells were able to adsorb 66.2 % of 100 μg L -1 Ce 3+ , 48.4 % of 250 μg L -1 Gd 3+ and 59.9 % of 1 mg L -1 La 3+ . The combination of extracellular polysaccharide and algal cell wall could adsorb 25.2 % of 100 μg L -1 Ce 3+ , 44.5 % of 250 μg L -1 Gd 3+ and 30.5 % of 1 mg L -1 La 3+ , respectively. These findings indicated that microalgae predominantly adsorbed REEs through the intracellular pathway. This study elucidates the mechanism of effective lipid accumulation and adsorption of REEs by microalgae under REEs stress conditions. It establishes a theoretical foundation for the efficient microalgae lipid production and REEs recovery from wastewater or waste residues containing REEs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Thallium (Tl + ) is a trace metal with extreme toxicity and is highly soluble in water, posing a great risk to ecological and human safety. This work aimed to investigate the role played by Tl + in regulating lipid accumulation in microalgae and the removal efficiency of Tl + . The effect of Tl + on the cell growth, lipid production and Tl + removal efficiency of Parachlorella kessleri R-3 was studied. Low concentrations of Tl + had no significant effect on the biomass of microalgae. When the Tl + concentration exceeded 5 μg L -1 , the biomass of microalgae showed significant decrease. The highest lipid content of 63.65% and lipid productivity of 334.55 mg L -1 d -1 were obtained in microalgae treated with 10 and 5 μg L -1 Tl + , respectively. Microalgae can efficiently remove Tl + and the Tl + removal efficiency can reach 100% at Tl + concentrations of 0-25 μg L -1 . The maximum nitric oxide (NO) level of 470.48 fluorescence intensity (1 × 10 6 cells) -1 and glutathione (GSH) content of 343.51 nmol g -1 (fresh alga) were obtained under 5 μg L -1 Tl + stress conditions. Furthermore, the exogenous donor sodium nitroprusside (SNP) supplemented with NO was induced in microalgae to obtain a high lipid content (59.99%), lipid productivity (397.99 mg L -1 d -1 ) and GSH content (430.22 nmol g -1 (fresh alga)). The corresponding analysis results indicated that NO could participate in the signal transduction pathway through modulation of reactive oxygen species (ROS) signaling to activate the antioxidant system by increasing the GSH content to eliminate oxidative damage induced by Tl + stress. In addition, NO regulation of ROS signaling may enhance transcription factors associated with lipid synthesis, which stimulates the expression of genes related to lipid synthesis, leading to increased lipid biosynthesis in microalgae. Moreover, it was found that the change in Tl + had little effect on the fatty acid components and biodiesel properties. This study showed that Tl + stress can promote lipid accumulation in microalgae for biodiesel production and simultaneously effectively remove Tl + , which provided evidence that NO was involved in signal transduction and antioxidant defense, and improved the understanding of the interrelation between NO and ROS to regulate lipid accumulation in microalgae., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In this study, a new microalgal strain, Asterarcys quadricellulare R-56, was isolated for biomass and lipid production. The effects of carbon and nitrogen sources and initial pH on the cell growth and lipid accumulation of strain R-56 were investigated. At 10 g L -1 glucose, 0.6 g L -1 sodium nitrate, and pH 7, the highest biomass of 4.18 g L -1 and lipid content of 43.66% were obtained. Microalgae had a broad pH tolerance in the range of 5-11, and the pH of the culture medium was close to neutral at the end of cultivation. The maximum contents of chlorophyll, carbohydrate, and protein under the recommended culture conditions were 19.47 mg mL -1 , 21.80%, and 29.94%, respectively. Palmitic and palmitoleic acid contents in strain R-56 accounted for as high as 83.73% of total fatty acids. This study suggested that strain R-56 was a promising lipid producer for high-quality biodiesel production., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Microalgae have become the hotspot of recent researches as heavy metals (HMs) adsorbent and biodiesel production feedstock. In this study, the cell growth, lipid production and Cr 6+ removal of Parachlorella kessleri R-3 at pH 3.5 and 15 °C were investigated. It was found that low concentration of Cr 6+ (0.5 to 2 mg/L) promoted the algal growth, whereas Cr 6+ higher than 5 mg/L inhibited the growth of P. kessleri R-3. Biomass concentration (2.40 g/L) and lipid productivity (131.79 mg/L d -1 ) reached the highest at 2 mg/L Cr 6+ , and lipid content (61.03 %) reached the highest at 5 mg/L Cr 6+ . The maximum Cr 6+ removal efficiency of 91 % was obtained at 0.5 mg/L Cr 6+ treatment. Furthermore, fatty acid composition analysis showed that strain R-3 had a high C16-18 content of 74.88-89.21 %. This study provides new insight into the treatment of HMs and lipid production in cold regions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In this study, a bioflocculation method assisted by fungal pellets was developed for highly efficient microalgae harvesting. Effects of critical parameters, including flocculation type, temperature, rotation speed and initial pH, on the bioflocculation of fungal Aspergillus niger for microalgae Scenedesmus sp. were investigated. Results showed that the maximum flocculation efficiency of 99.4% was obtained when the fungal pellets were inoculated in the algal solution at the initial pH of 8.0, temperature of 30 °C and rotation speed of 160 rpm for 48 h in BG-11 medium. Furthermore, microscopy examination, scanning electron microscopy, Fourier transform infrared spectroscopy, Zeta potential measurement and three-dimensional excitation emission matrix fluorescence spectroscopy were used to explore the mechanism of bioflocculation process. It was found that the interaction of fungi and microalgae was related to the surface functional groups of fungal pellets. This study provides a interpretation of conceivable mechanism for microalgal bioflocculation by fungal pellets., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, the growth and lipid accumulation of Scenedesmus sp. using different nanoparticles and light sources were investigated. Xenon lamp can produce a broad illumination spectrum, and exhibited better performance than light-emitting diode. SiC and g-C 3 N 4 nanoparticles improved the biomass and lipid accumulation, whereas TiO 2 and TiC nanoparticles had inhibitory influence on microalgae. Lipid production can be improved by oxidative stress produced by combination of nanoparticles and xenon lamp irradiation. At the optimal SiC nanoparticles concentration of 150 mg L -1 and photoperiod of 6:18 h, the maximum biomass concentration and total lipid content reached 3.18 g L -1 and 40.26%, respectively. The addition of SiC nanoparticles could promote the substrate utilization rate and induce stress condition, thereby enhancing the activity of acetyl-CoA carboxylase and lipid biosynthesis. This research shows that SiC nanoparticles addition combined with xenon lamp illumination is a promising strategy to promote microalgal growth and lipid accumulation., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this study, a novel integrated dark fermentative and microalgal bioreactor (IDFMB) was developed to simultaneously produce H 2 and lipid from food waste. Under the optimized working volume ratio of 1:4, starch concentration of 7 g L -1 and initial pH of 7.0, the highest H 2 production of 1643.5 mL L -1 and lipid yield of 515.6 mg L -1 were achieved. Microalgae can effectively utilize the main end products in dark fermentative effluent (acetic acid and butyric acid) for cell growth and lipid accumulation. Compared with single dark fermentation, the energy conversion efficiency from stimulated food waste was significantly enhanced by the IDFMB, which increased from 14.8% to 35%. Microbial community analysis revealed that Clostridium was the dominant bacteria for H 2 generation, and the IDFMB can improve the survival environment of microorganisms. This study provides a novel strategy for efficient energy recovery from food waste., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Ultrasonic treatment was applied to enhance the biomass and lipid accumulation of mixotrophic microalgae. The optimal microalgal ultrasonic power, ultrasonic frequency, ultrasonic interval and growth phase were 20 W, 20 Hz, 2 s and logarithmic phase, respectively. The maximum biomass concentration and lipid content reached 2.78 g L -1 and 28.5%, which were 26.9% and 37% higher than those of the control group. Microscope analysis shows that ultrasonic exposure caused tiny cracks or holes on the surface of cell walls, but did not damage the integrity of algal cell structure. After ultrasonic stimulation, the permeability of membrane and the transport of nutrients were improved, and the utilization rate of substrate and pigment concentration increased 22.7% and 18.4%, respectively. However, excessive ultrasonic irradiation significantly inhibited the cell growth and lipid accumulation of microalgae. This study indicates the feasibility and efficiency of using low-strength ultrasound in promoting biomass and lipid production of microalgae., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Anaerobic sludge (AS) and microalgae were co-cultured to enhance the energy conversion and nutrients removal from starch wastewater. Mixed ratio, starch concentration and initial pH played critical roles on the hydrogen and lipid production of the co-culture system. The maximum hydrogen production of 1508.3 mL L(-1) and total lipid concentration of 0.36 g L(-1) were obtained under the optimized mixed ratio (algae:AS) of 30:1, starch concentration of 6 g L(-1) and initial pH of 8. The main soluble metabolites in dark fermentation were acetate and butyrate, most of which can be consumed in co-cultivation. When sweet potato starch wastewater was used as the substrate, the highest COD, TN and TP removal and energy conversion efficiencies reached 80.5%, 88.7%, 80.1% and 34.2%, which were 176%, 178%, 200% and 119% higher than that of the control group (dark fermentation), respectively. This research provided a novel approach and achieved efficient simultaneous energy recovery and nutrients removal from starch wastewater by the co-culture system., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Effects of Fe(3+) (0-0.12 g/L), Mg(2+) (0-0.73 g/L) and Ca(2+) (0-0.98 g/L) on the biomass and lipid accumulation of heterotrophic microalgae were investigated in dark environment. The biomass and lipid production exhibited an increasing trend with increasing the concentrations of metal ions. In cultures with 1.2 × 10(-3) g/L Fe(3+), 7.3 × 10(-3) g/L Mg(2+) and 9.8 × 10(-4) g/L Ca(2+), the maximum biomass, total lipid content and lipid productivity reached 3.49 g/L, 47.4% and 275.7 mg/L/d, respectively. More importantly, EDTA addition (1.0 × 10(-3) g/L) could enhance the solubility of metal ions (iron and calcium) and increase their availability by microalgae, which evidently promote the lipid accumulation. Compared with the control, the total lipid content and lipid productivity increased 28.2% and 29.7%, respectively. These show that appropriate concentrations of metal ions and EDTA in the culture medium were beneficial to lipid accumulation of heterotrophic Scenedesmus sp. cells., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Growth and lipid production performance of Scenedesmus sp. under different culture modes were investigated. Under heterotrophic aerobic mode, algal biomass concentration and total lipid content reached 3.42 g L(-1) and 43.0 wt.%, which were much higher than those in autotrophic aerobic mode (0.55 g L(-1)/20.2 wt.%). The applied light exposure of 7.0 Wm(-2) was beneficial to biomass and lipid accumulation. Mixotrophic aerobic mode produced the highest biomass concentration of 3.84 g L(-1). The biomass was rich in lipids (51.3 wt.%) and low in proteins (17.9 wt.%) and carbohydrates (10.3 wt.%). However, lower algal biomass concentration (2.93 g L(-1)) and total lipid content (36.1 wt.%) were obtained in mixotrophic anaerobic mode. Mixotrophic aerobic mode gave the maximum heat value conversion efficiency of 45.7%. These results indicate that mixotrophic aerobic cultivation was a promising culture mode for lipid production by Scenedesmus sp., (Copyright © 2014 Elsevier Ltd. All rights reserved.)