Production of biomass and lipids by the oleaginous microalgae Monoraphidium sp. QLY-1 through heterotrophic cultivation and photo-chemical modulator induction

Exploring the nutritional potential of Monoraphidium littorale and enriched copepods as first feeds for rearing Nile tilapia (Oreochromis niloticus) larvae

One of the challenges in the aquaculture industry is providing nutritionally balanced and environmentally sustainable live food for fish larvae. Therefore, the rearing techniques of fish larvae with preferred starter food should be given importance for obtaining optimal hatchery production. Nile tilapia, Oreochromis niloticus larvae just after yolk absorption (body length 0.950 ± 0.004 mm; body weight 6.00 ± 0.02 mg) were reared in laboratory conditions for 16 days, feeding with 6 different diets to know their effect on survival and growth. The diets were live Monoraphidium littorale (T1), live enriched copepods with M. littorale (T2), powdered M. littorale (T3), powdered enriched copepods (T4), live M. littorale + live enriched copepods (T5), and powdered M. littorale + powdered enriched copepods (T6). The proximate composition, amino acid profile and fatty acid content of both M. littorale and copepods were analyzed. The biochemical analysis of the dried powder of enriched copepods and M. littorale revealed that both of them are excellent sources of protein, amino acids, and lipids, especially with monounsaturated and polyunsaturated fatty acids. The O. niloticus larvae fed the T2 diet exhibited the most favourable outcomes, with significantly higher larval gain in weight and percent weight gain, in comparison to the larvae fed other diets (p < 0.001 for all comparisons). The LG% and SGR of the larvae were also significantly higher in T2 in comparison to the T1, T3, T4, and T6 (p < 0.001 for all comparisons) except T5. In addition, the highest percent survival rate of the larvae was observed in T2 (95 %) followed by T4 (93 %), T6 (93 %), T3 (82 %), T5 (73 %) and then T1 (43 %). Based on the present findings, it is recommended that live copepods enriched with M. littorale can be utilized as a starter food for the rearing of Nile tilapia, O. niloticus larvae in hatcheries because of its enriched nutritional profile.

Optimization of stage conversion time and modification of cell metabolism to enhance lipid production of Auxenochlorella pyrenoidosa in two-stage cultivation

Traditionally, the time of maximum biomass concentration in stage I is the widely adopted stage conversion time in two-stage microalgae culture. This study challenges this conventional approach, demonstrating that the optimal stage conversion time in stage I is 72 h rather than 120 h for achieving maximum biomass concentration. A comparison of cell characteristics revealed that algal cells at 72 h exhibited better growth potential, leading to a higher biomass concentration after transfer to stage II and, consequently, increased lipid productivity. Moreover, the use of phosphorus repletion (5-fold) in stage II directed carbon flux toward biomass growth and lipid accumulation, thereby enhancing lipid productivity. By optimizing the stage conversion time and implementing phosphorus repletion, the mean lipid productivity of Auxenochlorella pyrenoidosa cultured under autotrophy-nitrogen starvation and autotrophy-high light conditions increased by 31 % and 60 %, respectively. This study underscores the importance of reevaluating the currently widely used stage conversion time.

Exogenous arginine promotes the coproduction of biomass and astaxanthin under high-light conditions in Haematococcus pluvialis

The economical way of Haematococcus pluvialis farming is to simultaneously achieve biomass, astaxanthin and lipid using less expensive chemicals. This paper explores the role of exogenous arginine in promoting growth and astaxanthin accumulation under stressful conditions. The application of arginine exerts a synergic effect on biomass, astaxanthin and lipid by improving carbon utilization, activating the arginine pathway and regulating carotenoid and lipid-related genes. Genes related to arginine catabolism, such as ADC, OCT, ASS1, NOS, and OAT, were up-regulated at both the cultivation and astaxanthin induction stages, signifying their importance in both growth and astaxanthin synthesis. Furthermore, transcriptome analysis revealed that arginine up-regulated transcription levels of genes involved carbon fixing, lipid biosynthesis, pyruvate metabolism, carotenoid, tricarboxylic acid cycle, and arginine and proline metabolism. The results provide a significant mechanism and applicability of using exogenous arginine and high light to stimulate bioproducts from Haematococcus pluvialis.

Salinity-Induced Physiochemical Alterations to Enhance Lipid Content in Oleaginous Microalgae Scenedesmus sp. BHU1 via Two-Stage Cultivation for Biodiesel Feedstock

In the recent past, various microalgae have been considered a renewable energy source for biofuel production, and their amount and extent can be enhanced by applying certain types of stress including salinity. Although microalgae growing under salinity stress result in a higher lipid content, they simultaneously reduce in growth and biomass output. To resolve this issue, the physiochemical changes in microalgae Scenedesmus sp. BHU1 have been assessed through two-stage cultivation. In stage-I, the maximum carbohydrate and lipid contents (39.55 and 34.10%) were found at a 0.4 M NaCl concentration, while in stage-II, the maximum carbohydrate and lipid contents (42.16 and 38.10%) were obtained in the 8-day-old culture. However, under increased salinity, Scenedesmus sp. BHU1 exhibited a decrease in photosynthetic attributes, including Chl-a, Chl-b, Fv/Fm, Y(II), Y(NPQ), NPQ, qP, qL, qN, and ETRmax but increased Y(NO) and carotenoids content. Apart from physiological attributes, osmoprotectants, stress biomarkers, and nonenzymatic antioxidants were also studied to elucidate the role of reactive oxygen species (ROS) facilitated lipid synthesis. Furthermore, elemental and mineral ion analysis of microalgal biomass was performed to evaluate the biomass quality for biofuel and cell homeostasis. Based on fluorometry analysis, we found the maximum neutral lipids in the 8-day-old grown culture at stage-II in Scenedesmus sp. BHU1. Furthermore, the use of Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy analyses confirmed the presence of higher levels of hydrocarbons and triacylglycerides (TAGs) composed of saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) in the 8-day-old culture. Therefore, Scenedesmus sp. BHU1 can be a promising microalga for potential biodiesel feedstock.

Glycine differentially improved the growth and biochemical composition of Synechocystis sp. PAK13 and Chlorella variabilis DT025

The potential of microalgae to produce valuable compounds has garnered considerable attention. However, there are various challenges that hinder their large-scale industrial utilization, such as high production costs and the complexities associated with achieving optimal growth conditions. Therefore, we investigated the effects of glycine at different concentrations on the growth and bioactive compounds production of Synechocystis sp. PAK13 and Chlorella variabilis cultivated under nitrogen availability. Glycine supplementation resulted in increased biomass and bioactive primary metabolites accumulation in both species. Sugar production, particularly glucose content, significantly improved in Synechocystis at 3.33 mM glycine (1.4 mg/g). This led to enhanced organic acid, particularly malic acid, and amino acids production. Glycine stress also influenced the concentration of indole-3-acetic acid, which was significantly higher in both species compared to the control. Furthermore, fatty acids content increased by 2.5-fold in Synechocystis and by 1.36-fold in Chlorella. Overall, the exogenous application of glycine is a cheap, safe, and effective approach to enhancing sustainable microalgal biomass and bioproducts production.

A strategy to promote carotenoids production in Dunaliella bardawil by melatonin combined with photoinduction

Microalgae are considered to be a very promising class of raw material for carotenoid production. In this study, melatonin (MLT), a widely used plant growth regulator, was added to the autotrophic medium of Dunaliella bardawil to explore its effects on the growth and pigment accumulation of Dunaliella bardawil. The results showed that the induction of exogenous MLT alone was not beneficial to the growth and pigment accumulation of Dunaliella bardawil, and the higher the concentration, the more obvious the inhibitory effect on the algal cells. Therefore, a strategy to promote carotenoid accumulation in Dunaliella bardawil by combining exogenous MLT and light induction was carried out. Under 4500 LUX light intensity, the content of zeaxanthin was significantly increased under exogenous MLT induction. In the 200 μg/mL, 300 μg/mL, and 400 μg/mL MLT-treated groups, the zeaxanthin single-cell content in the 300 μg/mL-treated group was as high as 0.38 ng/mL (0.17 ng/mL in the control group), which was 1.24-fold higher compared to the control. Under 9500 LUX light intensity, all carotenoids showed an increasing trend in all experimental groups, except for zeaxanthin, which showed a decreasing trend. The effect of 300 μg/mL showed the most obvious in the 200 μg/mL,300 μg/mL, and 400 μg/mL MLT treatment groups, where the lutein, α-carotene and β-carotene contents were 1.24, 1.14 and 1.31 times higher than those of the control group, respectively. Overall, exogenous MLT at high light intensities had a significant effect on pigment accumulation in Dunaliella bardawil.

Gamma-aminobutyric acid coupled with copper ion stress stimulates lipid production of green microalga Monoraphidium sp. QLY-1 through multiple mechanisms

Induction of copper ion (Cu²⁺) stress is a method used to increase lipid accumulation in microalgae, but it decreases cell growth. In this work, the impacts of gamma-aminobutyric acid (GABA) coupled with Cu²⁺ stress on the biomass and oil yield in Monoraphidium sp. QLY-1 were investigated. Results suggested that the combined treatment of GABA and Cu²⁺ resulted in a higher lipid content (55.13%) than Cu²⁺ treatment (48.43%). Furthermore, GABA addition upregulated the levels of lipid-relevant genes, cellular GABA, ethylene (ETH), and antioxidant enzyme activities and alleviated oxidative damage caused by Cu²⁺ stress. The autophagy-relevant gene atg8 was also upregulated by GABA treatment. Further exploration indicated that cell autophagy induced the lipid content up to 58.09% with GABA and Cu²⁺ stress treatment. This investigation demonstrates that the coupling strategy can stimulate lipid production and shed light on the underlying mechanisms in lipid biosynthesis, cell autophagy, and stress response of microalgae.

Coupling of myo-inositol with salinity regulates ethylene-induced microalgal lipid hyperproduction in molasses wastewater

With the goal of cost-effective and high-efficient microalgae-based biodiesel production, this study evaluated the feasibility of the joint strategy concerning myo-inositol (MI) and salinity stress on lipid productivity of Monoraphidium sp. QLY-1 in molasses wastewater (MW). The maximal lipid productivity (147.79 mg L^-1 d^-1) was obtained under combined 0.5 g L^-1 MI and 10 g L^-1 NaCl treatment, which was 1.40-fold higher than the control. Meanwhile, the nutrients removal from MW was markedly increased under MI-NaCl treatment. Moreover, exogenous MI upregulated key lipogenic genes' expressions, activated autophagic activity and ethylene (ET) signaling, and ultimately alleviated the salinity-induced damage via reactive oxygen species (ROS) signaling. Further pharmacologic experiment confirmed the indispensable role of ET in the lipogenesis progress under the combined treatment. These data demonstrated the combined salinity stress and MI treatment to be capable for lipid hyperproduction and wastewater nutrients removal, which contributes to practically integrating the microalgae cultivation with wastewater treatment.

A joint strategy comprising melatonin and 3-methyladenine to concurrently stimulate biomass and astaxanthin hyperaccumulation by Haematococcus pluvialis

Haematococcus pluvialis is a commercial microalgae used for natural astaxanthin production. This study aims to investigate the roles of melatonin (MT) and 3-methyladenine (3-MA) in regulating the cell growth and biosynthesis of astaxanthin and fatty acids under adverse conditions by H. pluvialis. Upon the dual treatments, the maximum astaxanthin concentration (46.78 mg L^-1) was 2.39- and 1.35-fold higher compared with the control and MT treatments, respectively. Concomitantly, the combined application of MT and 3-MA suppressed autophagy but promoted the production of biomass and lipids and upregulated carotenogenesis, lipogenesis and antioxidant enzyme-related genes at the transcriptional level, which were linked with astaxanthin and lipid biosynthesis and oxidative stress. Additionally, astaxanthin exhibited a noticeable increase under MT coupled with 3-MA in the other two strains of H. pluvialis. This study proposed a potential method for astaxanthin induction and provided insights into the function of autophagy in modulating cell growth and astaxanthin synthesis.

Fatty Acid Profile of Microalgal Oils as a Criterion for Selection of the Best Feedstock for Biodiesel Production

Microalgae are considered to be potentially attractive feedstocks for biodiesel production, mainly due to their fast growth rate and high oil content accumulated in their cells. In this study, the suitability for biofuel production was tested for Chlorella vulgaris, Chlorella fusca, Oocystis submarina, and Monoraphidium strain. The effect of nutrient limitation on microalgae biomass growth, lipid accumulation, ash content, fatty acid profile, and selected physico-chemical parameters of algal biodiesel were analysed. The study was carried out in vertical tubular photobioreactors of 100 L capacity. The highest biomass content at 100% medium dose was found for Monoraphidium 525 ± 29 mg·L−1. A 50% reduction of nutrients in the culture medium decreased the biomass content by 23% for O. submarina, 19% for Monoraphidium, 13% for C. vulgaris and 9% for C. fusca strain. Nutrient limitation increased lipid production and reduced ash content in microalgal cells. The highest values were observed for Oocystis submarina, with a 90% increase in lipids and a 45% decrease in ash content in the biomass under stress conditions. The fatty acid profile of particular microalgae strains was dominated by palmitic, oleic, linoleic, and linoleic acids. Nutrient stress increased the amount of saturated and unsaturated fatty acids affecting the quality of biodiesel, but this was determined by the type of strain.

Microalgae Cultivation Technologies as an Opportunity for Bioenergetic System Development—Advantages and Limitations

Microalgal biomass is currently considered as a sustainable and renewable feedstock for biofuel production (biohydrogen, biomethane, biodiesel) characterized by lower emissions of hazardous air pollutants than fossil fuels. Photobioreactors for microalgae growth can be exploited using many industrial and domestic wastes. It allows locating the commercial microalgal systems in areas that cannot be employed for agricultural purposes, i.e., near heating or wastewater treatment plants and other industrial facilities producing carbon dioxide and organic and nutrient compounds. Despite their high potential, the large-scale algal biomass production technologies are not popular because the systems for biomass production, separation, drainage, and conversion into energy carriers are difficult to explicitly assess and balance, considering the ecological and economical concerns. Most of the studies presented in the literature have been carried out on a small, laboratory scale. This significantly limits the possibility of obtaining reliable data for a comprehensive assessment of the efficiency of such solutions. Therefore, there is a need to verify the results in pilot-scale and the full technical-scale studies. This study summarizes the strengths and weaknesses of microalgal biomass production technologies for bioenergetic applications.

Cross-talk between gama-aminobutyric acid and calcium ion regulates lipid biosynthesis in Monoraphidium sp. QLY-1 in response to combined treatment of fulvic acid and salinity stress

In this study, the cross-talk between gama-aminobutyric acid (GABA) and calcium ion (Ca²⁺) signalling in the regulation of lipid production and cell growth in microalgae under fulvic acid and salinity stress (FA-salinity treatment) was investigated. GABA enhanced the lipid content and lipid productivity rate considerably, which were 1.27 and 1.29 times higher than those of the control, respectively. The levels of biosynthetic gene transcription, GSH, Ca²⁺ and cellular GABA were promoted by GABA addition, but decreased the ROS levels. Furthermore, the application of Ca²⁺ also increased lipid synthesis by regulating ROS and GABA signalling and lipogenesis-related genes. These results indicated that cytosolic GABA and Ca²⁺ levels exert crucial cross-talk in the modulation of cell growth and lipid accumulation induced by FA-salinity treatment. Collectively, this study demonstrated the beneficial effects caused by induction of the combination of chemical compounds on lipid production and provided new insights into lipid synthesis in microalgae.

Increased lipid synthesis in the culture of Chlorella homosphaera with magnetic fields application

This study aimed to investigate the influence of different intensities (15, 30 and 60 mT) and exposure times (1 h d^-1_, 24 h d^-1) of magnetic fields (MF) on the stimulation of lipid synthesis by the microalga Chlorella homosphaera. The growth and biochemical characterization of protein, carbohydrate and lipid content were determined. Biomass concentration increased by 20.6% (30 mT, 1 h d^-1) and 12.4% (60 mT, 1 h d^-1) in the presence of MF. However, biomass decreased by 33.0% (15 mT, 1 h d^-1) in relation to control cultivation (CC). The stress caused by the MF application stimulated lipid synthesis and biomass production. In all evaluated conditions, MF application showed a positive effect on lipid production; the application of 60 mT or 30 mT for 1 h d^-1 increased lipid productivity by 108.4% and 135.1%, respectively. MF application with ferrite magnets was thus efficient to stimulate lipid synthesis.

Comparative assessment of pretreatment strategies for production of microalgae-based biodiesel from locally isolated Chlorella homosphaera

The yield and quality of lipids extracted from microalgal biomass are critical factors in the production of microalgae-based biodiesel. The green microalga Chlorella homosphaera, isolated from Beira Lake, Colombo, Sri Lanka was employed in the present study to identify the effect of chlorophyll removal and cell disruption methods on lipid extraction yield, fatty acid methyl ester (FAME) profile and quality parameters of biodiesel; including cetane number (CN), iodine value (IV), degree of unsaturation (DU) and high heating value (HHV). In the first section of this study, chlorophyll was removed from dry microalgae biomass prior to lipid extraction. Through the analysis of FAME profiles, it was observed that chlorophyll removal yielded biodiesel of enhanced quality, albeit with a lipid loss of 44.2% relative to the control. In the second section of the study, mechanical cell disruption strategies including grinding, autoclaving, water bath heating and microwaving were employed to identify the most effective method to improve lipid recovery from chlorophyll-removed microalgae biomass. Autoclaving (121 °C, 20 min sterilization time, total time 2 h) was the most effective cell disruption technique of the methods tested, in terms of lipid extraction yield (39.80%) and also biodiesel quality. Moreover, it was observed that employing cell disruption subsequent to chlorophyll removal has a significant impact on the FAME profile of microalgae-based biodiesel, and consequently served to increase HHV and CN although IV and DU did not vary significantly.

Melatonin and calcium act synergistically to enhance the coproduction of astaxanthin and lipids in Haematococcus pluvialis under nitrogen deficiency and high light conditions

This study focused on the influence of integrating melatonin (MT) and calcium (Ca2+) on the simultaneous accumulation of astaxanthin and lipids in Haematococcus pluvialis under abiotic stress conditions. Compared with the control condition, MT induction enhanced astaxanthin and lipid contents by 65.89% and 27.38%, respectively. The highest contents of astaxanthin and lipids under combined exposure to MT and Ca2+ were 3.8% and 49.53%, respectively, which were 1.13- and 1.21-fold higher than those of cells treated with MT alone. The application of MT and Ca2+ also promoted the expression of carotenogenic and lipogenic genes and increased the levels of Ca2+ and γ-aminobutyric acid (GABA) but decreased reactive oxygen species (ROS) levels. Further evidence indicated that the increased cellular Ca2+ could promote astaxanthin biosynthesis under MT induction by regulating carotenogenic gene levels and GABA and ROS signalling. The integrated strategy efficiently improved the coproduction of astaxanthin and lipids in H. pluvialis.

Strigolactone mediates jasmonic acid-induced lipid production in microalga Monoraphidium sp. QLY-1 under nitrogen deficiency conditions

The roles of jasmonic acid (JA) in the regulation of cell growth and lipid biosynthesis under the combination of strigolactone (SL) treatment and nitrogen deficiency (ND) were investigated. In this work, the optimised ND condition (46.18%) and ND combined with SL treatment (53.71%) showed 1.11- and 1.29-fold increases in lipid content in Monoraphidium sp. QLY-1 compared with the control condition (41.57%). The levels of JA, glutathione (GSH), and γ-aminobutyric acid (GABA) and lipogenic genes expression were upregulated by the combination of SL and ND, but the ROS level was decreased. Furthermore, exogenous JA supplementation induced the highest lipid content (57.12%) and productivity (312.35 mg L-1 d-1) under ND combined with SL treatment. This study provided a combined strategy for enhancing lipid production and supplied novel insights into the role of JA signalling in regulating lipid synthesis and oxidative stress in microalgae by combining SL treatment with ND.

γ-Aminobutyric acid (GABA) regulates lipid production and cadmium uptake by Monoraphidium sp. QLY-1 under cadmium stress

This study explored the effects of γ-aminobutyric acid (GABA) on the production of biomass and lipids and on the uptake of Cd²⁺ by microalgae under cadmium (Cd) stress. Compared with the control and Cd stress alone, 2.5 mM GABA increased the maximum lipid content (55.37%) by 49.37% and 9.42%, respectively. GABA application resulted in increased contents of protein and glutathione (GSH) and in upregulated activity of α-amylase but decreased contents of starch, reactive oxygen species (ROS) and Cd²⁺, with no effect on subsequent biodiesel quality. Additional analysis of GABA further indicated that increased cellular GABA contents could promote lipid synthesis and reduce Cd accumulation by regulating the expression levels of lipogenesis genes, ROS signalling and mineral nutrient uptake under Cd stress. Collectively, these findings show that GABA not only increases lipid production in microalgae but also is involved in the mechanisms by which microalgae respond to Cd stress.

Characteristics of tropical freshwater microalgae Micractinium conductrix, Monoraphidium sp. and Choricystis parasitica, and their potency as biodiesel feedstock

The depletion of fossil fuel reserves requires advance anticipation through the search for alternative energy from renewable natural resources. Microalgae have been known as potential organisms for biodiesel feedstock. However, in order to be developed on a large scale, microalgae must have superior traits so that further development becomes more comfortable and cheaper. Tropical lakes are a source of superior microalgae adapted to moderate conditions which can later save operational costs in large-scale production. Situ Gintung and Situ Pamulang are the two largest lakes in South Tangerang, Indonesia and are potential sources of microalgae. Four microalgae isolates from both lakes have been identified, and their potential has been examined. Within an observation period of 18 days, they showed similar growth patterns reaching more than 10⁸ cells mL⁻¹ on day 14 and were able to resist increasing pH. The microalgae were identified through morphological observations and the sequencing of 23S rRNA genes with phylogenetic analysis. Each strain has a positive quality. Isolate G4-3, which was identified as Micractinium conductrix, and P5-4, which was identified as Monoraphidium sp., yielded biomass that exceeded 1.2 g L⁻¹ with lipid content exceeding 60%. Likewise, G4-9, which was also identified as Micractinium conductrix, and P2-15, which was identified as Choricystis parasitica, have lipid content which accounted for 89.10% and 57.48%, respectively; although their biomass was lower. The percentage of fatty acid methyl esters of the four microalgae achieved >60–80%; thus, meeting the standard of biodiesel properties. Therefore, the microalgae isolates have great potential for being developed as biodiesel feedstock.

Improvement in lipid production in Monoraphidium sp. QLY-1 by combining fulvic acid treatment and salinity stress

The effects of the combined treatment of fulvic acid (FA) and salinity stress on lipid production in Monoraphidium sp. QLY-1 at multiple levels was investigated in this study. The results indicated that the highest lipid content (59.53%) in QLY-1 was achieved by combining FA treatment and salinity stress. Compared with the control group and FA addition alone, the group treated with both FA and salinity stress had increased contents of reactive oxygen species (ROS), antioxidases, and nitric oxide (NO). Additionally, the addition of FA enhanced the expression levels of mitogen-activated protein kinases (MAPKs) and key genes related to lipid biosynthesis in QLY-1 under salinity stress. Collectively, biochemical analyses indicated that ROS, NO, MAPK, expression of lipid biosynthesis-related genes and antioxidant systems were involved in the lipid biosynthesis pathways of QLY-1 under the combined treatment of FA and salinity stress.

Enhancing biomass, lipid production, and nutrient utilization of the microalga Monoraphidium sp. QLZ-3 in walnut shell extracts supplemented with carbon dioxide

Microalgae are a promising biofuel resource, but their high cost and low productivity hinder their commercial applications. In the present study, Monoraphidium sp. QLZ-3 was cultivated in walnut shell extracts (WSE) supplemented with carbon dioxide (CO₂). Biomass was enhanced from 0.40 g L^-1 to 1.18 g L^-1, and lipid content reached 49.54% in WSE-12% CO₂ media. Biomass and lipid productivity reached 196.88 and 97.52 mg L^-1 d^-1, which were 1.33- and 1.57-fold higher than those of the control, respectively. The amount of carbohydrates increased, but the protein contents decreased. Furthermore, the application of CO₂ promoted nutrient and polyphenol absorption and upregulated the expression levels of lipid biosynthetic genes of this WSE-cultivated alga. These results indicated that coupling WSE and CO₂ could be an efficient strategy to enhance biofuel production by microalgae.

Response of lipid biosynthesis in Chlorella pyrenoidosa to intracellular reactive oxygen species level under stress conditions

An increase in the total lipid content in algal cells under stress conditions is often accompanied by an increase in reactive oxygen species (ROS). However, the link between these two events is unclear. In this study, the regulatory mechanism of ROS formation on lipid accumulation in C. pyrenoidosa was investigated using a Fenton-like reaction. A high Spearman correlation coefficient of 0.901 was obtained between the Hydroxyl radical (OH) level and lipid content. Importantly, the increase in the total lipid content was clearly coupled with a significant increase in the intracellular OH concentration rather than increases in the H₂O₂ and O₂^- concentrations. Transcriptome data confirms that most of the differential expression genes (DEGs) involved in fatty acid and glycerolipid biosynthesis were up-regulated by the increased OH under stress conditions. These results reveal that lipid accumulation in algal cells was promoted by OH.

Enhancement of lipid accumulation in Monoraphidium sp. QLY-1 by induction of strigolactone

In this study, the effects of strigolactone (SL) on the biomass, lipid content, biochemical properties, and gene transcription of Monoraphidium sp. QLY-1 were examined. The lipid content and lipid productivity increased by 61% and 55% in QLY-1 under 1 μM SL induction compared to the control group, respectively. SL also upregulated the levels of endogenous NO and Ca²⁺ and lipid biosynthesis gene transcription. Subsequently, the relationship between Ca²⁺ and nitric oxide (NO) in the regulation of cell growth and lipid accumulation of QLY-1 under SL induction conditions was analysed. An increase in endogenous Ca²⁺ regulated cell growth and lipid biosynthesis by modulating the levels of NO and lipid biosynthesis-related gene expression. Collectively, this study provided a valuable approach for biofuel production from microalgae under SL induction and demonstrated that there is crucial crosstalk between the Ca²⁺ and NO signalling in the manipulation of lipid biosynthesis in microalgae under SL treatment.

Monoraphidium sp. HDMA-20 is a new potential source of α-linolenic acid and eicosatetraenoic acid

BACKGROUND

ω-3 polyunsaturated fatty acids (PUFAs) are synthesized from α-Linolenic acid (ALA, C18:3ω3) and play important roles in anti-inflammatory and antioxidant responses in mammal cells. ALA is an essential fatty acid which cannot be produced within the human body and must be acquired through diet. The purpose of this study was to evaluate the potential of a novel microalgal strain (HDMA-20) as a source of ω-3 PUFAs including ALA and eicosatetraenoic acid (ETA, C20:4ω3).

METHOD

Phylogenetic Neighbor-Joining analysis based on 18S ribosomal DNA sequence was used to identify the microalga strain HDMA-20. Autotrophic condition was chosen to cultivate HDMA-20 to reduce the cultivation cost. GC-MS was used to determine the fatty acid composition of HDMA-20 lipid.

RESULTS

A microalgal strain (HDMA-20) from Lake Chengfeng (Daqing, Heilongjiang province, China) was found to accumulate high content of ω-3 PUFAs (63.4% of total lipid), with ALA and eicosatetraenoic acid (ETA, C20:4ω3) accounting for 35.4 and 9.6% of total lipid, respectively. Phylogenetic analysis based on 18S ribosomal DNA sequences suggested that the HDMA-20 belonged to genus Monoraphidium (Selenastraceae, Sphaeropleales) and its 18S rDNA sequence information turned out to be new molecular record of Monoraphidium species. The biomass productivity and lipid content of HDMA-20 were also investigated under autotrophic condition. The biomass productivity of HDMA-20 reached 36.3 mg L^- 1 day^- 1, and the lipid contents was 22.6% of dry weight.

CONCLUSION

HDMA-20 not only represent an additional source of ALA, but also a totally new source of ETA. The high content of ω-3 PUFAs, especially ALA, of HDMA-20, makes it suitable as a source of nutrition supplements for human health. In addition, HDMA-20 exhibited good properties in growth and lipid accumulation, implying its potential for cost-effective ω-3 PUFAs production in future.

Coupling of abiotic stresses and phytohormones for the production of lipids and high-value by-products by microalgae: A review

Microalgae can produce lipids and high-value by-products under abiotic stress conditions, including nutrient starvation, high light intensity, extreme temperature, high salinity and the presence of heavy metals. However, the growth and development of microalgae and the accumulation of metabolites may be inhibited by adverse stresses. In recent years, phytohormones have emerged as a topic of intense focus in microalgae research. Phytohormones could sustain the growth of microalgae under abiotic stress conditions. In addition, the combination of plant hormones and abiotic stresses could further promote the biosynthesis of metabolites and improve the ability of microalgae to tolerate abiotic stresses. This review primarily focuses on the regulatory effects of exogenous phytohormones on the biosynthesis of metabolites by microalgae under adverse environmental conditions and discusses the mechanisms of phytohormone-mediated cell growth, stress tolerance and lipid biosynthesis in microalgae under abiotic stress conditions.

Isolation of a novel strain of Monoraphidium sp. and characterization of its potential for α-linolenic acid and biodiesel production

α-Linolenic acid (ALA) is an essential fatty acid which cannot be synthesized de novo in mammals and must be ingested regularly in the diet. In this study, a microalgal strain named HDMA-11 was isolated from Lake Ming, China, and was found to accumulate a high ALA content (39.2% of total lipids). Phylogenetic neighbor-joining analysis indicated that HDMA-11 belongs to the genus Monoraphidium (Selenastraceae, Sphaeropleales) and its 18S ribosomal DNA sequence seemed to be a new molecular record of a Monoraphidium species. The fatty acid profiles, biomass productivity and lipid content of HDMA-11 were also investigated in autotrophic conditions. The high levels of polyunsaturated fatty acids in HDMA-11, especially ALA, make it suitable as a source of nutritional supplementation for human health. Furthermore, HDMA-11 exhibited good properties for biodiesel production, characterized by high lipid content (28.5% of dry weight), moderate biomass productivity (31.5 mg L^-1 day^-1) and a promising lipid profile.

Butylated hydroxytoluene induces astaxanthin and lipid production in Haematococcus pluvialis under high-light and nitrogen-deficiency conditions

The aim of this study was to investigate the effects of butylated hydroxytoluene (BHT) on the production of astaxanthin and lipids in Haematococcus pluvialis LUGU under high-light and nitrogen-deficiency conditions. Astaxanthin and lipid contents were increased by 71.13% and 10.71%, respectively, in algal cells treated with 2 mg L^-1 BHT. The maximal contents of astaxanthin and lipids were 3.17% and 46%, respectively. The levels of reactive oxygen species (ROS) in the presence of BHT were lower than in the control, and this effect involved strong activation of several antioxidases. Additionally, BHT application upregulated endogenous nitric oxide (NO) production. These results showed that this approach is useful for stimulating production of astaxanthin and lipids in H. pluvialis and that exogenous BHT induces astaxanthin and lipid production, which is responsible for the signalling molecule responses against abiotic stress conditions in H. pluvialis.

Use of fatty acids in the chemotaxonomy of the family Selenastraceae (Sphaeropleales, Chlorophyceae)

The family Selenastraceae includes many species of freshwater green microalgae with morphological characteristics that are so subtly different that it is difficult to discriminate species within it. Therefore, the use of the diacritical characteristics of traditional morphological taxonomy may be ineffective at differentiating among many species of the family. Chemotaxonomy based on fatty acid methyl ester (FAME) can help resolve uncertainties not completely addressed by other approaches, such as molecular studies of some species within the Selenastraceae. Here, we first tested three techniques for the analysis of microalgal FAME to choose the one that would provide the best profiles for chemotaxonomy: 1) direct transesterification (DT) of the biomass followed by gas chromatography coupled to mass spectrometry analysis (GC-MS); 2) extraction using chloroform and methanol, followed by transesterification (T) and then analysis by gas chromatography/flame ionization detector (GC-FID); and 3) extraction with chloroform and methanol and then separation into lipid classes using thin-layer chromatography (TLC) using the Iatroscan-Chromarod system. The tests were conducted on 12 strains (11 species) of Selenastraceae and one outgroup strain. The fatty acid profiles produced by the DT-GC-MS technique yielded the best results for the chemotaxonomy of the Selenastraceae species using 12 FAME. The proportion of the variance in the fatty acid profiles obtained with DT-GC-MS analysis explained by species was 85%, whereas the differences explained by strains was 92%. Therefore, DT-GC-MS was used to analyze other microalgae strains, totaling 15 species of 8 genera of green coccoid microalgae, including the recently described Curvastrum. The results with all strains showed that fatty acid profiles obtained by DT-GC-MS were significantly different (p < 0.001) among strains and among species. The variance in fatty acids profiles explained by separation into strains was 97%, whereas the separation into species explained 93% of the variance. Statistical analyses showed that, for our dataset, the C₁₈ fatty acids 18:3ω3 and 18:4ω6 were indicative of the Selenastraceae. Therefore, fatty acid profiles are a useful auxiliary chemotaxonomic tool for species identification in Selenastraceae.

Melatonin enhances lipid production in Monoraphidium sp. QLY-1 under nitrogen deficiency conditions via a multi-level mechanism

In this study, melatonin (MT) promoted lipid accumulation in Monoraphidium sp. QLY-1 under nitrogen deficiency conditions. The lipid accumulation increased 1.22- and 1.36-fold compared with a nitrogen-starved medium and a normal BG-11 medium, respectively. The maximum lipid content was 51.38%. The reactive oxygen species (ROS) level in the presence of melatonin was lower than that in the control group, likely because of the high antioxidant activities. The application of melatonin upregulated the gibberellin acid (GA) production and rbcL and accD expression levels but downregulated the abscisic acid (ABA) content and pepc expression levels. These findings demonstrated that exogenous melatonin could further improve the lipid production in Monoraphidium sp. QLY-1 by regulating antioxidant systems, signalling molecules, and lipid biosynthesis-related gene expression under nitrogen deficiency conditions.

A strategy for promoting lipid production in green microalgae Monoraphidium sp. QLY-1 by combined melatonin and photoinduction

Microalgae lipids are potential candidates for the production of renewable biodiesel. The combination of plant hormones and two-step cultivation regulates lipid production in microalgae. A strategy for promoting lipid accumulation in Monoraphidium sp. QLY-1 by combining exogenous melatonin (MT) and photoinduction was developed. The effects of melatonin on the lipid content, reactive oxygen species (ROS), and activities of three key fatty acid biosynthetic enzyme in Monoraphidium sp. QLY-1 were investigated. The lipid content increased by 1.32-fold under 1μM melatonin treatment. The maximum lipid content achieved was 49.6%. However, the protein and carbohydrate contents decreased rapidly from 57.21% to 47.96% and from 53.4% to 37.71%, respectively. Biochemical and physiological analyses suggested that the ROS and lipid biosynthesis-related enzyme activities correlated with increased lipid accumulation under photo-melatonin induction conditions.

Endophytic Bacteria Isolated from Panax ginseng Improves Ginsenoside Accumulation in Adventitious Ginseng Root Culture

Ginsenoside is the most important secondary metabolite of ginseng. Natural sources of wild ginseng have been overexploited. Although root culture could reduce the length of the growth cycle of ginseng, the number of ginsenosides is fewer and their contents are lower in adventitious roots of ginseng than that in ginseng cultivated in the field. In this study, we investigated the effects of endophytic bacterial elicitors on biomass and ginsenoside production in adventitious roots cultures of Panax ginseng. Endophyte LB 5-3 as an elicitor could increase biomass and ginsenoside accumulation in ginseng adventitious root culture. After 6 days elicitation with a 10.0 mL of strain LB 5-3, the content of total ginsenoside was 2.026 mg g⁻¹ which was four times more than that in unchallenged roots. The combination of methyl jasmonate and strain LB 5-3 had a negative effect on ginseng adventitious root growth and ginsenoside production. The genomic DNA of strain LB 5-3 was sequenced, and was found to be most closely related to Bacillus altitudinis (KX230132.1). The challenged ginseng adventitious root extracts exerted inhibitory effect against the HepG2 cells, which IC₅₀ value was 0.94 mg mL⁻¹.

Effect of fulvic acid induction on the physiology, metabolism, and lipid biosynthesis-related gene transcription of Monoraphidium sp. FXY-10

Fulvic acid (FA) triggers lipid accumulation in Monoraphidium sp. FXY-10, which can produce biofuels. Therefore, the metabolism shift and gene expression changes influenced by fulvic acid should be investigated. In this study, lipid and protein contents increased rapidly from 44.6% to 54.3% and from 31.4% to 39.7% under FA treatment, respectively. By contrast, carbohydrate content sharply declined from 49.5% to 32.5%. The correlation between lipid content and gene expression was also analyzed. Results revealed that accD, ME, and GPAT genes were significantly correlated with lipid accumulation. These genes could likely influence lipid accumulation and could be selected as modification candidates. These results demonstrated that FA significantly increased microalgal lipid accumulation by changing the intracellular reactive oxygen species, gene expression, and enzyme activities of acetyl-CoA carboxylase, malic enzyme, and phosphoenolpyruvate carboxylase.

Strategies for Lipid Production Improvement in Microalgae as a Biodiesel Feedstock

In response to the energy crisis, global warming, and climate changes, microalgae have received a great deal of attention as a biofuel feedstock. Due to a high lipid content in microalgal cells, microalgae present as a promising alternative source for the production of biodiesel. Environmental and culturing condition variations can alter lipid production as well as chemical compositions of microalgae. Therefore, application of the strategies to activate lipid accumulation opens the door for lipid overproduction in microalgae. Until now, many original studies regarding the approaches for enhanced microalgal lipid production have been reported in an effort to push forward the production of microalgal biodiesel. However, the current literature demonstrates fragmented information available regarding the strategies for lipid production improvement. From the systematic point of view, the review highlights the main approaches for microalgal lipid accumulation induction to expedite the application of microalgal biodiesel as an alternative to fossil diesel for sustainable environment. Of the several strategies discussed, the one that is most commonly applied is the design of nutrient (e.g., nitrogen, phosphorus, and sulfur) starvation or limitation. Other viable approaches such as light intensity, temperature, carbon dioxide, salinity stress, and metal influence can also achieve enhanced microalgal lipid production.