Chemicals to enhance microalgal growth and accumulation of high-value bioproducts

Synergistic effect of selenium and gibberellic acid for enhanced biomass, lipid and improved biodiesel quality from Tetradesmus obliquus through response surface methodology

Biodiesel production from microalgae presents an innovative solution for renewable energy. This study investigates biodiesel production using Tetradesmus obliquus ON506010.1 by optimizing substrates, selenium and gibberellic acid. Using 15 µg/L selenium, lipid content and biomass productivity reached 35.45 %±0.92 and 0.178 g/L/day ± 0.051. With 50 µM gibberellic acid, biomass productivity and lipid content peaked at 0.785 ± 0.101 g/L/day and 38.95 %±0.35, surpassing the control. Fatty acid composition, biodiesel properties, and mRNA expression of lipid synthesis enzymes (acetyl CoA carboxylase (ACC) and fatty acid desaturase (FAD)) correlated. Combining 10 µg/L selenium with 75 µM gibberellic acid with response surface methodology (RSM) increased lipid content (42.80 % ±0.11) and biomass productivity (0.964 g/L/day ± 0.128). ACC and FAD upregulation validated this enhancement, with a 4.4-fold increase in FAD expression. Fatty acid composition and most biodiesel properties met international standards demonstrating Tetradesmus obliquus ON506010.1's potential for sustainable biodiesel production with better cold flow property and oxidative stability.

Enhancing high-density microalgae cultivation via exogenous supplementation of biostimulant derived from onion peel waste for sustainable biodiesel production

Microalgae demonstrate significant potential as a source of liquid-based biofuels. However, increasing biomass productivity in existing cultivation systems is a critical prerequisite for their successful integration into large-scale operations. Thus, the current work aimed to accelerate the growth of C. vulgaris via exogenous supplementation of biostimulant derived from onion peel waste. Under the optimal growth conditions, which entailed a biostimulant dosage of 37.5% v/v, a pH of 3, an air flow rate of 0.4 L/min, and a 2% v/v inoculum harvested during the mid-log phase, yielded a maximum biomass concentration of 1.865 g/L. Under the arbitrarily optimized parameters, a comparable growth pattern was evident in the upscaled cultivation of C. vulgaris, underscoring the potential commercial viability of the biostimulant. The biostimulant, characterized through gas chromatography-mass spectrometry (GC-MS) analysis, revealed a composition rich in polyphenolic and organo-sulphur compounds, notably including allyl trisulfide (28.13%), methyl allyl trisulfide (23.04%), and allyl disulfide (20.78%), showcasing potent antioxidant properties. Additionally, microalgae treated with the biostimulant consistently retained their lipid content at 18.44% without any significant reduction. Furthermore, a significant rise in saturated fatty acid (SFA) content was observed, with C16:0 and C18:1 dominating both bench-scale (44.08% and 14.01%) and upscaled (51.12% and 13.07%) microalgae cultures, in contrast to the control group where C18:2 was prevalent. Consequently, SFA contents reached 54.35% and 65.43% in bench-scale and upscaled samples respectively, compared to 33.73% in the control culture. These compositional characteristics align well with the requirements for producing high-quality crude biodiesel.

Simultaneous production of high-value lipids in Schizochytrium sp. by synergism of chemical modulators

The study focuses on the simultaneous improvement of biomass, lipid, and docosahexaenoic acid (DHA) productivities in a single reactor using modulator control strategies. The efficacy of three different biochemical modulators, sesamol (Ses), 6-benzylaminopurine (6-BAP), and ethylenediaminetetraacetic acid (EDTA), as potential stimulants in augmenting the biomass, lipid, and DHA production of Schizochytrium sp. MTCC 5890 was elucidated. After 48 h of cultivation, among tested modulators, the individual supplementation of 6-BAP and Ses showed improvement in biomass, lipid, and DHA accumulation by 28.2%, 56.1%, and 87.2% and 21.7%, 47.9%, and 91%, respectively, over the non-supplemented group. In addition, the cooperative effect of selected concentrations, i.e., 10 mgL-1 6-BAP and 200 mgL-1 Ses, further increased the productivities of biomass of 13.5 gL-1d-1 ± 0.66, lipid of 7.4 gL-1d-1 ± 0.69, and DHA of 3.2 gL-1d-1 ± 1.09 representing 8%, 39%, and 69% increase over the individual addition of 6-BAP or Ses, respectively, in batch culture. Supplementation with 6-BAP + Ses at 12 h of time point eventually increased the lipid yield to 15.6 ± 0.42 gL-1 from 7.88 ± 0.31 gL-1 (control) and DHA yield to 6.4 ± 0.11 gL-1 from 2.23 ± 0.09 gL-1 (control), respectively. Furthermore, the process was optimized in continuous culture supplemented with 6-BAP + Ses for enhanced productivities. Continuous culture resulted in maximum biomass (2.04 ± 1.12 gL-1 day-1), lipid (1.0 ± 0.73 gL-1 day-1), and DHA (0.386 ± 0.22 gL-1 day-1) productivities, which were higher as compared with the batch and fed-batch processes by 26 ± 1.21%, 22 ± 1.01%, and 21 ± 0.98% and 24 ± 0.45%, 16 ± 0.38%, and 14 ± 0.12%, respectively. This work represents the potential application of the combined effect of modulators for the simultaneous enhancement of biomass production and lipid and DHA productivities. KEY POINTS: • The cumulative study of 6-BAP and sesamol proved to be more efficient in the simultaneous production of biomass, lipid, and DHA in a single reactor. • Addition of a combination of 6-BAP + Ses remarkably increased the biomass, lipid, and DHA productivities in tandem in continuous culture.

Propanol and 1, 3-propanediol enhance fatty acid accumulation synergistically in Schizochytrium ATCC 20888

The effects of propanol and 1, 3-propanediol on fatty acid and biomass accumulation in Schizochytrium ATCC 20888 were explored. Propanol increased the contents of saturated fatty acids and total fatty acids by 55.4 and15.3%, while 1, 3-propanediol elevated the polyunsaturated fatty acids, total fatty acids and biomass contents by 30.7, 17.0, and 6.89%. Although both of them quench ROS to increase fatty acids biosynthesis, the mechanisms are different. The effect of propanol did not reflect on metabolic level while 1, 3-propanediol elevated osmoregulators contents and activated triacylglycerol biosynthetic pathway. The triacylglycerol content and the ratio of polyunsaturated fatty acids to saturated fatty acids were significantly increased by 2.53-fold, which explained the higher PUFA accumulation in Schizochytrium after adding 1, 3- propanediol. At last, the combination of propanol and 1, 3-propanediol further elevated total fatty acids by approximately 1.2-fold without compromising cell growth. These findings are valuable for scale-up production of designed Schizochytrium oil for various application purposes.

Emerging Trends of Nanotechnology and Genetic Engineering in Cyanobacteria to Optimize Production for Future Applications

Nanotechnology has the potential to revolutionize various fields of research and development. Multiple nanoparticles employed in a nanotechnology process are the magic elixir that provides unique features that are not present in the component's natural form. In the framework of contemporary research, it is inappropriate to synthesize microparticles employing procedures that include noxious elements. For this reason, scientists are investigating safer ways to produce genetically improved Cyanobacteria, which has many novel features and acts as a potential candidate for nanoparticle synthesis. In recent decades, cyanobacteria have garnered significant interest due to their prospective nanotechnological uses. This review will outline the applications of genetically engineered cyanobacteria in the field of nanotechnology and discuss its challenges and future potential. The evolution of cyanobacterial strains by genetic engineering is subsequently outlined. Furthermore, the recombination approaches that may be used to increase the industrial potential of cyanobacteria are discussed. This review provides an overview of the research undertaken to increase the commercial avenues of cyanobacteria and attempts to explain prospective topics for future research.

Algal biorefinery culminating multiple value-added products: recent advances, emerging trends, opportunities, and challenges

Algal biorefinery is rising as a prominent solution to economically fulfill the escalating global requirement for nutrition, feed, fuel, and medicines. In recent years, scientific productiveness associated with microalgae-based studies has elaborated in multiplied aspects, while translation to the commercial level continues to be missing. The present microalgal biorefinery has a challenge in long-term viability due to escalated market price of algal-mediated biofuels and bioproducts. Advancements are required in a few aspects like improvement in algae processing, energy investment, and cost analysis of microalgae biorefinery. Therefore, it is essential to recognize the modern work by understanding the knowledge gaps and hotspots driving business scale up. The microalgae biorefinery integrated with energy-based products, bioactive and green compounds, focusing on a circular bioeconomy, is urgently needed. A detailed investigation of techno-economic analysis (TEA) and life cycle assessment (LCA) is important to increase the market value of algal products. This review discusses the valorization of algal biomass for the value-added application that holds a sustainable approach and cost-competitive algal biorefinery. The current industries, policies, technology transfer trends, challenges, and future economic outlook are discussed. This study is an overview through scientometric investigation attempt to describe the research development contributing to this rising field.

Isolation of Haematococcus lacustris as source of novel anti-multi-antibiotic resistant microbes agents; fractionation and identification of bioactive compounds

In this work, freshwater microalga, Haematococcus lacustris was isolated from the River Nile, identified and deposited in genebank under name of H. lacustris isolate REH10 with accession number OK336515. N-hexane extract was produced high inhibition effects against multi-antibiotic resistant pathogens. The n-Hexane extract was fractionated and 2 fractions (F3 & F4) exhibited high antibacterial activity (15 - 20 mm) compared with other fractions. Thus, they sub-fractionated and 2 sub-fractions produced from the F3 had high inhibition activity against all tested pathogens (18-20 mm). To identify the main compounds responsible for inhibition growth of multi-drug resistance bacteria, GC-MS chromatogram analyses was applied on the F3 and its sub-fractions 2 and 3. Five compounds detected in the 2 sub-fractions. Palmitic acid was identified as the first report antibacterial agent. The antioxidant activity of SF3-3 was reached to 86 and 80.5% for DPPH and ABTS.⁺ tests, respectively.

Influence of exogenous phytohormone supplementation on the pigment and fatty acid content of three marine diatoms

Diatoms are ubiquitous photosynthetic microorganisms with great potential for biotechnological applications. However, their commercialisation is hampered by production costs, requiring hence optimisation of cultivation methods. Phytohormones are plant growth regulators which may be used to influence physiological processes in microalgae, including diatoms. In this study, the model species Phaeodactylum tricornutum (Phaeodactylaceae) and two Irish isolates of Stauroneis sp. (Stauroneidaceae) and Nitzschia sp. (Bacillariaceae) were grown with varying amounts of the phytohormones indoleacetic acid (IAA), gibberellic acid (GA3), methyl jasmonate (MJ), abscisic acid (ABA) or salicylic acid (SA), and their influence on pigment and fatty acid profiles was monitored. The application of GA3 (200 mg/l) stimulated the growth of P. tricornutum which accumulated 52% more dry biomass compared to the control and concomitantly returned the highest eicosapentaenoic acid (EPA) yield (0.6 mg/l). The highest fucoxanthin yield (0.18 mg/l) was obtained for P. tricornutum cultivated with GA3 (2 mg/l) supplementation. In Stauroneis sp., SA (1 mg/l) had the most positive effect on EPA, the content of which was enhanced up to 45.7 μg/mg (4.6% of total dry weight). The SA (1 mg/l) treatment also boosted carotenogenesis in Nitzschia sp., leading to 1.7- and 14-fold increases in fucoxanthin and β-carotene compared to the control, respectively. Of note, MJ (0.5 mg/l) increased the EPA content of all diatom species compared to their controls. These results indicate that phytohormone-based treatments can be used to alter the pigment and lipid content of microalgae, which tend to respond in dose- and species-specific manners to individual compounds.Key points• Response to phytohormones was investigated in diatoms from distinct families.• MJ (0.5 mg/l) caused an increase in EPA cellular content in all three diatoms.• Phytohormones mostly caused dose-dependent and species-specific responses.

Strain Development in Microalgal Biotechnology-Random Mutagenesis Techniques

Microalgal biomass and metabolites can be used as a renewable source of nutrition, pharmaceuticals and energy to maintain or improve the quality of human life. Microalgae’s high volumetric productivity and low impact on the environment make them a promising raw material in terms of both ecology and economics. To optimize biotechnological processes with microalgae, improving the productivity and robustness of the cell factories is a major step towards economically viable bioprocesses. This review provides an overview of random mutagenesis techniques that are applied to microalgal cell factories, with a particular focus on physical and chemical mutagens, mutagenesis conditions and mutant characteristics.

Salt-alkalization may potentially promote Microcystis aeruginosa blooms and the production of microcystin-LR

The development of saline-alkali lands has contributed to the increasing discharge of alkaline salt-laden wastewater, which poses a threat to aquatic organisms. However, the comprehensive effect of alkaline salt on Microcystis aeruginosa, a harmful cyanobacterium, remains unclear. In this study, the growth, physiology, cell ultrastructure and production of microcystin-LR (MC-LR) in Microcystis aeruginosa exposed to four levels of alkaline salt stress were evaluated. The growth of Microcystis aeruginosa was stimulated at an electrical conductivity (EC) of 2.5 mS/cm compared to the control, as supported by the increased cell density, photosynthetic pigment and protein contents. Microcystis aeruginosa could tolerate a certain level of alkaline salt (i.e., EC of 5 mS/cm) via increasing photosynthetic pigment contents to protect cells from alkaline salt stress, but the antioxidant defence system and cell ultrastructure were not affected. When EC increased to 7.5 mS/cm, alkaline salt caused oxidative stress and toxicity in Microcystis aeruginosa, as evidenced by analysis of the integrated biomarker response (IBR). Furthermore, the photosynthetic pigment and protein contents decreased, and cell apoptosis associated with ultrastructural changes was observed. Therefore, we propose that EC of 7.5 mS/cm is a threshold for growth of Microcystis aeruginosa. Additionally, the intracellular MC-LR content was stimulated by alkaline salt, and the highest value was observed at EC of 2.5 mS/cm. The extracellular MC-LR content increased with the increasing alkaline salt concentration. When EC was 7.5 mS/cm, the extracellular MC-LR content was significantly higher than in the control and was associated with the upregulated mcyH gene. This study recommends that more attention should be paid to the risk of Microcystis aeruginosa bloom and microcystin-LR pollution in lakes located in salinization regions.

The Growth, Lipid Accumulation and Fatty Acid Profile Analysis by Abscisic Acid and Indol-3-Acetic Acid Induced in Chlorella sp. FACHB-8

Microalgae are considered a promising source for biodiesel. The addition of plant hormone can exert a significant impact on the production of microalgae biomass and lipid accumulation. Nevertheless, the response of microalgae cells to hormones is species- or strain-dependent. It remains controversial which genes involved in strong increase of fatty acids production in response to abscisic acid (ABA) in Chlorella sp. FACHB-8 strain. We investigated cell growth, lipid accumulation, and fatty acid composition when ABA and indol-3-acetic acid (IAA) were used in the growth medium of Chlorella sp. FACHB-8. The four treatments, including 5 mg/L IAA (E1), 10 mg/L IAA (E2), 10 mg/L ABA (E3), the combination of 5 mg/L IAA and 5 mg/L ABA (E4), were found to increase cell growth, but only 10 mg/L ABA treatment could enhance the lipid accumulation. The fatty acid profile was changed by the addition of ABA, making fatty acids afflux from polyunsaturated fatty acids to monounsaturated and saturated fatty acids, which were suitable for diesel application. Furthermore, a transcriptome analysis was conducted, unraveling the differentially expressed genes enriched in fatty acid biosynthesis, fatty acid metabolism, and biosynthesis of the unsaturated fatty acid pathway in response to ABA. Our results clarified the correlation of fatty acid synthesis-related genes and fatty acid profiles, helping understand the potential response mechanism of Chlorella sp. FACHB-8 strain respond to ABA treatment.

Enhancement of lipid accumulation and docosahexaenoic acid synthesis in Schizochytrium sp. H016 by exogenous supplementation of sesamol

Schizochytrium sp. is one of the most promising marine oleaginous microorganisms for industrial production of docosahexaenoic acid (DHA). In this study, the exogenous supplementation of 1 mM sesamol to the fermentation medium effectively prevented the peroxidation of polyunsaturated fatty acids in the fermentation process, which thereby significantly increasing the lipid and DHA yield by 53.52% and 78.30%, respectively. The addition of sesamol also increased the total antioxidant capacity of cells and induce the gene expression of polyketide synthase and antioxidant enzyme system. Moreover, the supply of nicotinamide adenine dinucleotide phosphate was regulated by sesamol by inhibiting the malic enzyme activity and promoting the glucose-6-phosphate dehydrogenase activity. Finally, fed-batch fermentation showed that the addition of sesamol significantly enhanced the DHA yield by 90.76%. This study provides an important reference for enhancing the DHA productivity of Schizochytrium sp. in industrial fermentation.

The Active Phytohormone in Microalgae: The Characteristics, Efficient Detection, and Their Adversity Resistance Applications

Phytohormones are a class of small organic molecules that are widely used in higher plants and microalgae as chemical messengers. Phytohormones play a regulatory role in the physiological metabolism of cells, including promoting cell division, increasing stress tolerance, and improving photosynthetic efficiency, and thereby increasing biomass, oil, chlorophyll, and protein content. However, traditional abiotic stress methods for inducing the accumulation of energy storage substances in microalgae, such as high light intensity, high salinity, and heavy metals, will affect the growth of microalgae and will ultimately limit the efficient accumulation of energy storage substances. Therefore, the addition of phytohormones not only helps to reduce production costs but also improves the efficiency of biofuel utilization. However, accurate and sensitive phytohormones determination and analytical methods are the basis for plant hormone research. In this study, the characteristics of phytohormones in microalgae and research progress for regulating the accumulation of energy storage substances in microalgae by exogenous phytohormones, combined with abiotic stress conditions at home and abroad, are summarized. The possible metabolic mechanism of phytohormones in microalgae is discussed, and possible future research directions are put forward, which provide a theoretical basis for the application of phytohormones in microalgae.

Iron and methyl jasmonate increase high-value PUFA production by elevating the expression of desaturase genes in marine microalga Isochrysis sp

AIM

This study investigated the effect of several metabolic enhancers on the expression of fatty acid biosynthetic genes and their influence on the production of high-value PUFA in the marine microalgae Isochrysis sp., CASA CC 101.

METHODS AND RESULTS

The effect of the presence of iron (Fe), nicotinic acid (NIC), methyl jasmonate (MJ) and thidiazuron (TDZ) on the expression of the fatty acid desaturase genes Δ6Des, Δ5Des and Δ4Des was studied in cultures of the marine microalga Isochrysis sp., CASA CC 101. The production of high-value PUFA like γ-linolenic acid (GLA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was correlated with these gene expressions. The results showed that MJ, Fe and TDZ significantly increased the lipid content than the control. MJ specifically up-regulated ∆6Des gene expression and thereby increased GLA production. Whereas Fe specifically increased ∆5Des gene expression and thereby increased EPA production. However, Fe and TDZ-treated cells effectively upregulated the expression of ∆4Des and increased the production of DHA when compared with control cells.

CONCLUSIONS

Our findings suggest that addition of Fe and MJ in the culture medium triggers the expression of PUFA biosynthetic genes, especially ∆6Des and ∆4Des, in marine microalga Isochrysis sp., CASA CC 101 their presence resulted in increased production of the PUFAs GLA, EPA and DHA.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that the addition of Fe and MJ to the culture media of Isochrysis sp., CASA CC 101 results in up-regulation of its genes Δ4Des, Δ6Des and Δ5Des, and improves the production of PUFA. Therefore, the addition of Fe and MJ to the culture medium is useful to increase the production of high-value PUFA in Isochrysis sp., CASA CC 101 and also to the other micro algal species.

Anti-Inflammatory and Anticancer Effects of Microalgal Carotenoids

Acute inflammation is a key component of the immune system's response to pathogens, toxic agents, or tissue injury, involving the stimulation of defense mechanisms aimed to removing pathogenic factors and restoring tissue homeostasis. However, uncontrolled acute inflammatory response may lead to chronic inflammation, which is involved in the development of many diseases, including cancer. Nowadays, the need to find new potential therapeutic compounds has raised the worldwide scientific interest to study the marine environment. Specifically, microalgae are considered rich sources of bioactive molecules, such as carotenoids, which are natural isoprenoid pigments with important beneficial effects for health due to their biological activities. Carotenoids are essential nutrients for mammals, but they are unable to synthesize them; instead, a dietary intake of these compounds is required. Carotenoids are classified as carotenes (hydrocarbon carotenoids), such as α- and β-carotene, and xanthophylls (oxygenate derivatives) including zeaxanthin, astaxanthin, fucoxanthin, lutein, α- and β-cryptoxanthin, and canthaxanthin. This review summarizes the present up-to-date knowledge of the anti-inflammatory and anticancer activities of microalgal carotenoids both in vitro and in vivo, as well as the latest status of human studies for their potential use in prevention and treatment of inflammatory diseases and cancer.

E/Z isomerization of astaxanthin and its monoesters in vitro under the exposure to light or heat and in overilluminated Haematococcus pluvialis cells

Thermo- and photoisomerization of astaxanthin was investigated in a model system (solutions in methanol and chloroform), and the dynamics of astaxanthin isomers and esters content was analyzed in Haematococcus pluvialis green algal cells exposed to factors inducing astaxanthin accumulation. In both systems, the astaxanthin isomerization process seems to be defined by a) the action of light (or heat), and b) the dielectric constant of the surrounding medium. Upon heating, the accumulation of Z-isomers occurred in a model system during the entire incubation period. For the first 5 h of illumination, both Z-isomers accumulated in the solutions up to 5%, and then their content decreased. The accumulated amount of the Z-isomers in the cells of H. pluvialis was found to reach 42% of the total content of astaxanthin initially, and then it decreased during the experiment. The results lead to a conclusion that both cultivation of H. pluvialis culture in specific conditions and heat treatment of the resulting extracts from it might be efficient for obtaining large amounts of economically useful astaxanthin Z-isomer.

Role of extracellular polymeric substances on nutrients storage and transfer in algal-bacteria symbiosis sludge system treating wastewater

This study reported the role and significance of extracellular polymeric substances (EPSs) on nutrients storage and transfer in an algal-bacteria symbiosis sludge (ABSS) system for wastewater treatment, and the novel algae-based sequencing batch suspended biofilm reactor (A-SBSBR, Ra) was selected as model of ABSS system. Results showed that compared to conventional SBSBR, the EPS of Ra performed better storage for NO₂^--N, NO₃^--N, total phosphorus and PO₄^3- -P, with increase ratios of 43.7%, 36.0%, 34.1% and 14.7% in sludge phase and 174.0%, 147.4%, 150.4% and 122.0% in biofilm phase, respectively. The analysis of mechanisms demonstrated that microalgae active transport and uptake for divalent cations could enhance their local concentrations around ABS flocs and partially neutralized negative charge of EPSs, and more anions related to nutrients were absorbed in EPSs. Moreover, O₂ produced by microalgae photosynthesis enhanced bacteria activity and improved the production of EPSs in both sludge and biofilm phases.

Antioxidant Production in Dunaliella

Microalgae have become an attractive natural source of a diverse range of biomolecules, including enzymatic and non-enzymatic antioxidants; nevertheless, economically sustainable production of such compounds from microalgae biomass is still challenging. The main hurdles are: (a) increasing microalgae yield; (b) achieving optimal cultivation conditions; (c) energy-efficient and cost-effective downstream processing (extraction and purification); (d) optimal storage of post-processed antioxidant molecules. This review provides a detailed overview of enzymatic and non-enzymatic antioxidants in the cellular metabolism of the commercially important microalgae Dunaliella, industrial applications of antioxidant enzymes, strategies to enhanced antioxidant accumulation in cells, and the opportunities and limitations of current technologies for antioxidant enzymes production from microalgae biomass as an alternative to common microbial sources.

Toward the Enhancement of Microalgal Metabolite Production through Microalgae-Bacteria Consortia

Engineered mutualistic consortia of microalgae and bacteria may be a means of assembling a novel combination of metabolic capabilities with potential biotechnological advantages. Microalgae are promising organisms for the sustainable production of metabolites of commercial interest, such as lipids, carbohydrates, pigments, and proteins. Several studies reveal that microalgae growth and cellular storage of these metabolites can be enhanced significantly by co-cultivation with growth-promoting bacteria. This review summarizes the state of the art of microalgae-bacteria consortia for the production of microalgal metabolites. We discuss the current knowledge on microalgae-bacteria mutualism and the mechanisms of bacteria to enhance microalgae metabolism. Furthermore, the potential routes for a microalgae-bacteria biorefinery are outlined in an attempt to overcome the economic failures and negative energy balances of the existing production processes.

Haematococcus pluvialis Accumulated Lipid and Astaxanthin in a Moderate and Sustainable Way by the Self-Protection Mechanism of Salicylic Acid Under Sodium Acetate Stress

To elucidate the mechanism underlying increased fatty acid and astaxanthin accumulation in Haematococcus pluvialis, transcriptome analysis was performed to gain insights into the multiple defensive systems elicited by salicylic acid combined with sodium acetate (SAHS) stresses with a time course. Totally, 112,886 unigenes and 61,323 non-repeat genes were identified, and genes involved in carbon metabolism, primary and secondary metabolism, and immune system responses were identified. The results revealed that SA and NaAC provide both energy and precursors to improve cell growth of H. pluvialis and enhance carbon assimilation, astaxanthin, and fatty acids production in this microalga with an effective mechanism. Interestingly, SA was considered to play an important role in lowering transcriptional activity of the fatty acid and astaxanthin biosynthesis genes through self-protection metabolism in H. pluvialis, leading to its adaption to HS stress and finally avoiding massive cell death. Moreover, positive correlations between 15 key genes involved in astaxanthin and fatty acid biosynthesis pathways were found, revealing cooperative relation between these pathways at the transcription level. These results not only enriched our knowledge of the astaxanthin accumulation mechanism in H. pluvialis but also provided a new view on increasing astaxanthin production in H. pluvialis by a moderate and sustainable way in the future.

Recent advancements in mixotrophic bioprocessing for production of high value microalgal products

Recently, microalgal biomass has become an attractive and sustainable feedstock for renewable production of various biochemicals and biofuels. However, attaining required productivity remains a key challenge to develop industrial applications. Fortunately, mixotrophic cultivation strategy (MCS) is leading to higher productivity due to the metabolic ability of some microalgal strain to utilise both photosynthesis and organic carbon compared to phototrophic or heterotrophic processes. The potential of MCS is being explored by researchers for maximized biochemicals and biofuels production however it requires further development yet to reach commercialization stage. In this review, recent developments in the MCS bioprocess for selective value-added (carotenoids) products have been reviewed; synergistic mechanism of carbon and energy was conferred. Moreover, the metabolic regulation of microalgae under MCS for utilized carbon forms and carbon recycling was demonstrated; Additionally, the opportunities and challenges of large-scale MCS have been discussed.

Biodegradation of Doxylamine From Wastewater by a Green Microalga, Scenedesmus obliquus

Pharmaceutical contaminants (PCs) have been recognized as emerging contaminants causing unexpected consequences to environment and humans. There is an urgent need for development of efficient technologies to treat these PCs from water. The current study has investigated the removal capacity of a green microalgal species, Scenedesmus obliquus, for doxylamine, chemical oxygen demand (COD), and nutrients from real wastewater. Results have indicated that S. obliquus can grow well in the doxylamine-polluted wastewater with the achievement of 56, 78.5, 100, and 89% removal of doxylamine, COD, total nitrogen (TN), and total phosphorus (TP). Addition of 2 g L^-1 bicarbonate enhanced the removal of doxylamine up to 63% and slightly inhibited the removal of COD. Decreased carbohydrate (28-26%) and increased protein content (30-33%) of the harvested biomass have been observed after cultivation in the wastewater. The current study has shown the feasibility of using microalgae-based biotechnologies for PC-contaminated wastewater.

Biotechnological production of astaxanthin from the microalga Haematococcus pluvialis

Although biotechnologies for astaxanthin production from Haematococcus pluvialis have been developed for decades and many production facilities have been established throughout the world, the production cost is still high. This paper is to evaluate the current production processes and production facilities, to analyze the R&D strategies for process improvement, and to review the recent research advances shedding light on production cost reduction. With these efforts being made, we intent to conclude that the production cost of astaxanthin from Haematococcus might be substantially reduced to the levels comparable to that of chemical astaxanthin through further R&D and the future research might need to focus on strain selection and improvement, cultivation process optimization, innovation of cultivation methodologies, and revolution of extraction technologies.

Enhancement of astaxanthin production by Haematococcus pluvialis using magnesium aminoclay nanoparticles

Improving the content and production of high-value ketocarotenoid pigments is critical for the commercialization of microalgal biorefineries. This study reported the use of magnesium aminoclay (MgAC) nanoparticles for enhancement of astaxanthin production by Haematococcus pluvialis in photoautotrophic cultures. Addition of 1.0 g/L MgAC significantly promoted cellular astaxanthin biosynthesis (302 ± 69 pg/cell), presumably by inducing tolerable oxidative stress, corresponding to a 13.7-fold higher production compared to that in the MgAC-untreated control (22 ± 2 pg/cell). The lipid content and cell size of H. pluvialis improved by 13.6- and 2.1-fold, respectively, compared to that of the control. Despite reduced cell numbers, the overall astaxanthin production (10.3 ± 0.4 mg/L) improved by 40% compared to the control (7.3 ± 0.6 mg/L), owing to improved biomass production. However, an MgAC dosage above 1.0 g/L inhibited biomass production by inducing electrostatic cell wall destabilization and aggregation. Therefore, MgAC-induced stimulation of algae varies widely based on their morphological and physiological characteristics.

Plant hormone induced enrichment of Chlorella sp. omega-3 fatty acids

BACKGROUND

Omega-3 fatty acids have various health benefits in combating against neurological problems, cancers, cardiac problems and hypertriglyceridemia. The main dietary omega-3 fatty acids are obtained from marine fish. Due to the pollution of marine environment, recently microalgae are considered as the promising source for the omega-3 fatty acid production. However, the demand and high production cost associated with microalgal biomass make it necessary to implement novel strategies in improving the biomass and omega-3 fatty acids from microalgae.

RESULTS

Four plant hormones zeatin, indole acetic acid (IAA), gibberellic acid (GBA) and abscisic acid (ABA) were investigated for their effect on the production of biomass and lipid in isolated Chlorella sp. The cells showed an increase of the biomass and lipid content after treatments with the plant hormones where the highest stimulatory effect was observed in ABA-treated cells. On the other hand, IAA showed the highest stimulatory effect on the omega-3 fatty acids content, eicosapentaenoic acid (EPA) (23.25%) and docosahexaenoic acid (DHA) (26.06%). On the other hand, cells treated with ABA had highest lipid content suitable for the biodiesel applications. The determination of ROS markers, antioxidant enzymes, and fatty acid biosynthesis genes after plant hormones treatment helped elucidate the mechanism underlying the improvement in biomass, lipid content and omega-3 fatty acids. All four plant hormones upregulated the fatty acid biosynthesis genes, whereas IAA particularly increased omega-3-fatty acids as a result of the upregulation of omega-3 fatty acid desaturase.

CONCLUSIONS

The contents of omega-3 fatty acids, the clinically important compounds, were considerably improved in IAA-treated cells. The highest lipid content obtained from ABA-treated biomass can be used for biodiesel application according to its biodiesel properties. The EPA and DHA enriched ethyl esters are an approved form of omega-3 fatty acids by US Food and Drug Administration (FDA) which can be utilized as the therapeutic treatment for the severe hypertriglyceridemia.

Application of chemicals for enhancing lipid production in microalgae-a short review

Microalgae have attracted great attention as a promising sustainable resource for biofuel production. In studies aiming to improve lipid accumulation, many key enzymes involved in lipid biosynthesis were identified and confirmed, but genetic engineering remains a challenge in most species of microalgae. In an alternative approach, various chemical modulators can be used to directly regulate the lipid biosynthesis pathway, with similar effects to gene overexpression and interference approaches, including improving the precursor supply and blocking competing pathways. The produced lipid can be protected from being converted into other metabolites by the chemicals such as lipase inhibitors. In addition, a few chemicals were also demonstrated to greatly influence cell growth and lipid accumulation by indirect regulation of the lipid biosynthesis pathway, such as increasing cell permeability or regulating oxidative stress. Thus, adding chemical modulators can be a useful alternative strategy for improving lipid accumulation in large-scale cultivation of microalgae.

Rapid induction of edible lipids in Chlorella by mild electric stimulation

In this work, a new stress-based method for rapid induction of triacylglycerol (TAG) and total and polyunsaturated fatty acid accumulations in Chlorella sp. by mild electric stimulation is presented. When a cathodic current of 31 mA (voltage: 4 V) was applied to the algal cells for 4 h, the TAG content of the electro-treated cells was sharply increased to a level 2.1 times that of the untreated control. The contents of the polyunsaturated linoleic (C18:2n6) and linolenic (C18:3n3) acids in the electro-treated cells were also 36 and 57% higher than those in the untreated cells, respectively. Cyclic voltammetry and various biochemical analyses indicate that TAG and fatty acid formations are electro-stimulated via de novo fatty acid biosynthesis and metabolic transformation in the Chlorella cells.

Identification of Antimicrobial Peptides from the Microalgae Tetraselmis suecica (Kylin) Butcher and Bactericidal Activity Improvement

The outburst of microbial resistance to antibiotics creates the need for new sources of active compounds for the treatment of pathogenic microorganisms. Marine microalgae are of particular interest in this context because they have developed tolerance and defense strategies to resist the exposure to pathogenic bacteria, viruses, and fungi in the aquatic environment. Although antimicrobial activities have been reported for some microalgae, natural algal bioactive peptides have not been described yet. In this work, acid extracts from the microalga Tetraselmis suecica with antibacterial activity were analyzed, and de novo sequences of peptides were determined. Synthetic peptides and their alanine and lysine analogs allowed identifying key residues and increasing their antibacterial activity. Additionally, it was determined that the localization of positive charges within the peptide sequence influences the secondary structure with tendency to form an alpha helical structure.

Algae colonisation of brick pavement at the University of Venda: A potential slippery hazard

A brick pavement, tramped by humans, is exposed to atmospheric elements, thus allowing cyanobacteria and algae to colonise. In this article, we report on the factors that contribute to the slipperiness of a brick pavement at the University of Venda in the Limpopo province of the South Africa. Samples were collected from brick surfaces either colonised by green algae (treated) or not (control). The samples were acid-digested and analysed for metals by Inductively Coupled Plasma Mass Spectrometry (ICP MS) in parts per billion (ppb). The treated bricks, with green algae, had average high metal contents (ppb): Al 9456.02, Ti 731.23, V 46.44, Cr 78.85, Mn 862.93, Fe 16295.18, Co 23.57, Ni 59.36, Cu 66.31, Zn 160.57, As 7.92, Se 10.45, Mo 6.74, Cd 5.19, Sn 4.65, Sb 2.31 and Pb 19.51. In contrast, control bricks had a low average of metal content (ppb) as follows: Al 2.99, Ti 0.28, V 4.04, Cr 1.42, Mn 4.29, Fe 20.89, Co 0.36, Ni 2.74, Cu 5.64, Zn 4.21, As 0.56, Se <3.00, Mo 0.88, Cd 0.01, Sn 1.05, Sb 0.04 and Pb 0.04. Other factors that promote algae colonisation include high solar radiation, neutral pH, nutrients, low electrical conductivity and total dissolved solids. The algae colonisation of brick pavement results in an unaesthetic sighting and a slippery surface that is hazardous to humans.

Sodium azide intervention, salinity stress and two-step cultivation of Dunaliella tertiolecta for lipid accumulation

A two-step strategy was employed to culture Dunaliella tertiolecta, an oleaginous unicellular green alga, combined by the salt stress and sodium azide intervention, to observe their effects on its lipid accumulation. When the algae cultured at different salt concentrations reached the logarithmic growth phase, sodium azide was added. The results showed that the addition of sodium azide significantly increased the lipid content and had no significant effect on cell biomass. The lipid yield and single cell lipid content under 50 μM sodium azide increased by 10.4% and 21.7%. Under the two-step culture condition, combining of the treatment of 50 μM sodium azide and 2.5 M salt stress, the total lipid productivity and single-cell lipid content were 10% and 70.5% higher than that of the control. It seemed that sodium azide and salinity might have a synergistic effect on the lipid accumulation of D. tertiolecta. It can be concluded that sodium azide is an effective inducer of lipid accumulation in D. tertiolecta, and two-stage cultivation is a feasible way to improve lipid accumulation in microalgae.

The influence of four pharmaceuticals on Chlorellapyrenoidosa culture

There has been a developing technology in algae with pharmaceuticals wastewater. However, the effect and the underlying mechanism of pharmaceuticals on algae are not well understood. To investigate the effect and mechanism of pharmaceuticalson microalgae, four pharmaceuticals of clofibric acid (CLF), ciprofloxacin (CIP), diclofenac (DCF) and carbamazepine (CBZ) on C. pyrenoidosa culture were analyzed. At low concentrations (<10 mg/L), the pharmaceuticals, especially the DCF, exhibited positive effects on both the structure and function of algal cultures; algal growth (i.e., chlorophyll a accumulation, lipid accumulation) and activities of antioxidant enzymes were stimulated. The algal metabolite differences of various DCF concentrations were investigated and a total of 91 substances were identified, whose samples were clustered and clearly separated. The key metabolomics pathway analysis found that the DCF promoted the carbohydrate and fatty acid metabolic pathway in C. pyrenoidosa under relatively low concentrations (<10 mg/L). However, the algae metabolomics pathway was disturbed significantly under the action of a high concentration of DCF (>100 mg/L). The study detected the effects of four pharmaceuticals on C. pyrenoidosa and demonstrated that the usage of metabolomics analysis complemented with DCF could be an effective approach to understand the mechanism of molecular evolution in C. pyrenoidosa for microalgal biomass and bioenergy from wastewater in researches of biological resources.

Ameliorating the Metabolic Burden of the Co-expression of Secreted Fungal Cellulases in a High Lipid-Accumulating Yarrowia lipolytica Strain by Medium C/N Ratio and a Chemical Chaperone

Yarrowia lipolytica, known to accumulate lipids intracellularly, lacks the cellulolytic enzymes needed to break down solid biomass directly. This study aimed to evaluate the potential metabolic burden of expressing core cellulolytic enzymes in an engineered high lipid-accumulating strain of Y. lipolytica. Three fungal cellulases, Talaromyces emersonii-Trichoderma reesei chimeric cellobiohydrolase I (chimeric-CBH I), T. reesei cellobiohydrolase II (CBH II), and T. reesei endoglucanase II (EG II) were expressed using three constitutive strong promoters as a single integrative expression block in a recently engineered lipid hyper-accumulating strain of Y. lipolytica (HA1). In yeast extract-peptone-dextrose (YPD) medium, the resulting cellulase co-expressing transformant YL165-1 had the chimeric-CBH I, CBH II, and EG II secretion titers being 26, 17, and 132 mg L^-1, respectively. Cellulase co-expression in YL165-1 in culture media with a moderate C/N ratio of ∼4.5 unexpectedly resulted in a nearly two-fold reduction in cellular lipid accumulation compared to the parental control strain, a sign of cellular metabolic drain. Such metabolic drain was ameliorated when grown in media with a high C/N ratio of 59 having a higher glucose utilization rate that led to approximately twofold more cell mass and threefold more lipid production per liter culture compared to parental control strain, suggesting cross-talk between cellulase and lipid production, both of which involve the endoplasmic reticulum (ER). Most importantly, we found that the chemical chaperone, trimethylamine N-oxide dihydride increased glucose utilization, cell mass and total lipid titer in the transformants, suggesting further amelioration of the metabolic drain. This is the first study examining lipid production in cellulase-expressing Y. lipolytica strains under various C/N ratio media and with a chemical chaperone highlighting the metabolic complexity for developing robust, cellulolytic and lipogenic yeast strains.

Screening chemical modulators of benzoic acid derivatives to improve lipid accumulation in Schizochytrium limacinum SR21 with metabolomics analysis

BACKGROUND

Schizochytrium sp. is a marine fungus with great potential as an alternative commercial source of lipids rich in polyunsaturated fatty acids (PUFAs). To further increase lipid accumulation in Schizochytrium sp., the effect of exogenous additives has become one of the hotspots of current research. Although benzoic acid derivatives showed positive effects on lipid accumulation in Schizochytrium, the biochemical mechanism needs further investigation.

RESULTS

Four benzoic acid derivatives (sodium benzoate, p-aminobenzoic acid, p-methyl benzoic acid and folic acid) were screened and evaluated for their effect on lipid accumulation in Schizochytrium limacinum SR21. The lipid yield was increased by 56.84% with p-aminobenzoic acid (p-ABA) at a concentration of 200 mg/L among the four tested chemical modulators. The metabolomics analysis showed that 200 mg/L p-ABA was optimal for promoting glucose catabolism in glycolysis with an increase in the mevalonate pathway and a weakening of the tricarboxylic acid (TCA) cycle. Moreover, p-ABA increased NADPH generation by enhancing the pentose phosphate pathway (PPP), ultimately redirecting the metabolic flux to lipid synthesis. Fed-batch fermentation further proved that p-ABA could significantly increase the yield of lipid by 30.01%, reaching 99.67 g/L, and the lipid content was increased by 35.03%, reaching 71.12%. More importantly, the yields of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were increased by 33.28% and 42.0%, respectively.

CONCLUSION

The addition of p-ABA could promote the synthesis of tetrahydrofolate, enhancing NADPH, which ultimately promoted the flow of carbon flux to lipid synthesis. These findings provide a valuable strategy for improving the lipid accumulation in Schizochytrium by additives.

Evaluation of oleaginous eustigmatophycean microalgae as potential biorefinery feedstock for the production of palmitoleic acid and biodiesel

This study aimed to evaluate the potential of six oleaginous eustigmatophytes for use as biorefinery feedstock for the co-production of palmitoleic acid (PA) and biodiesel under different initial nitrogen concentrations (INCs). Six eustigmatophytes were studied, the nitrogen deficiency strategy significantly stimulated the simultaneous hyper-accumulation of PA and lipids, and led to a desirable fatty acid profile (FAP), except in Vacuoliviride sp. and Nannochloropsis oculata. Particularly, Eustigmatos cf. polyphem exhibited great potential when supplied with 1 mM INC and yielded the highest PA (29.71% of dry weight (DW)) and lipid (72.01% of DW) contents, as their productivities increased to 96.26 and 232.79 mg/L/d, respectively. Furthermore, neutral lipids accounted for 91.82% of the total lipids and were rich in PA, and the favourable FAPs of C16-C18 (87.95%) and monounsaturated FAs (70.10%) ensured good biodiesel properties including the cetane number (55.69) and iodine value (92.81 gI₂/100 g), and all met the standard requirements.

Chemically-Induced Production of Anti-Inflammatory Molecules in Microalgae

Microalgae have been widely recognized as a valuable source of natural, bioactive molecules that can benefit human health. Some molecules of commercial value synthesized by the microalgal metabolism have been proven to display anti-inflammatory activity, including the carotenoids lutein and astaxanthin, the fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), and sulphated polysaccharides. These molecules can accumulate to a certain extent in a diversity of microalgae species. A production process could become commercially feasible if the productivity is high and the overall production process costs are minimized. The productivity of anti-inflammatory molecules depends on each algal species and the cultivation conditions, the latter being mostly related to nutrient starvation and/or extremes of temperature and/or light intensity. Furthermore, novel bioprocess tools have been reported which might improve the biosynthesis yields and productivity of those target molecules and reduce production costs simultaneously. Such novel tools include the use of chemical triggers or enhancers to improve algal growth and/or accumulation of bioactive molecules, the algal growth in foam and the surfactant-mediated extraction of valuable compounds. Taken together, the recent findings suggest that the combined use of novel bioprocess strategies could improve the technical efficiency and commercial feasibility of valuable microalgal bioproducts production, particularly anti-inflammatory compounds, in large scale processes.

Rapid selection of astaxanthin-hyperproducing Haematococcus mutant via azide-based colorimetric assay combined with oil-based astaxanthin extraction

The aim of this work was to develop a new approach for simple and high-throughput selection of astaxanthin-hyperproducing Haematococcus mutants through a sequential combination method of azide-based colorimetric assessment and oil-based astaxanthin quantification. Randomly mutagenized cells were spotted on solid culture medium containing 50 µM of sodium azide to accelerate the biosynthesis of astaxanthin. After 3 days, highly-induced mutants were preliminarily isolated by visual inspection and their astaxanthin accumulations were rapidly quantified by soybean oil-based extraction method. On the whole, the selected mutants showed reduced vegetative growth rates but eventually exhibited higher astaxanthin productions than the parental strain owing to their improved inductive growths. Among them, M13 showed 174.7 ± 5.69 mg L^-1 of the highest astaxanthin production, which is 1.59-times higher than that of wild-type. This wide-scope screening method expedites both upstream and downstream astaxanthin quantification, making it a useful tool for isolating microalgae with high astaxanthin production.

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.

Optimization of nutrient stress using C. pyrenoidosa for lipid and biodiesel production in integration with remediation in dairy industry wastewater using response surface methodology

The present study illustrates optimization and synergetic potential of alga Chlorella pyrenoidosa for lipid production and remediation of Dairy industry wastewater (DIWW) through response surface methodology (RSM). Maximum lipid productivity of 34.41% was obtained under 50% DIWW supplemented with 0 mg L^-1 nitrate (NO₃^-), and 50 mg L^-1 phosphate (PO₄^-3). While maximum biomass productivity (1.54 g L^-1) was obtained with 50% DIWW supplemented with 100 mg L^-1 NO₃^-, and 50 mg L^-1, PO₄^-3. Maximum removal of COD (43.47%), NO₃^- (99.80%) and PO₄^-3 (98.24%) was achieved with 8th run (75% DIWW, 150 mg L^-1 NO₃^-, 75 mg L^-1 PO₄^-3), 15th run (50% DIWW, 0 mg L^-1 NO₃^-, 50 mg L^-1, PO₄^- 3) followed by 1st run (25% DIWW, 50 mg L^-1 NO₃^-, and 25 mg L^-1, PO₄^-3), respectively. Lipid (bio-oil) obtained from 15th run of experiment was converted in biodiesel through base catalyze transesterification process. Fatty acid methyl ester (FAME) analysis of biodiesel confirmed the presence of major fatty acids in C. pyrenoidosa grown in DIWW were C11:0, C14:0, C16:0, C16:1, C18:1 and C18:2. Results of study clearly demonstrate enhanced growth and lipid accumulation by C. pyrenoidosa in surplus PO₄^-3 and limitation of NO₃^- sources with DIWW and its suitability as potential alternative for commercial utilization.

Identification and Functional Analysis of the psaD Promoter of Chlorella vulgaris Using Heterologous Model Strains

Chlorella has great potential as a bio-factory for production of value-added compounds. To produce the desired chemicals more efficiently in Chlorella, genetic tools for modification of Chlorella need to be developed, especially an endogenous promoter. In this study, the promoter of photosystem I protein D (psaD) from Chlorella vulgaris UTEX395 was identified. Computational analysis revealed the presence of several putative cis-acting elements, including a potential core element, and light-responsive or stress-responsive elements. Gene expression analysis in heterologous expression system in Chlamydomonasreinhardtii and Nicotianabenthamiana showed that CvpsaD promoter can be used to drive the expression of genes. Functional analysis of this promoter suggested that the initiator element (Inr) is important for its function (i.e., TATA-less promoter) and that an additional factor (e.g., downstream of the transcriptional start site) might be needed for light response. We have shown that the CvpsaD promoter is functional, but not sufficiently strong, both in microalgae and higher plant.

Screening of chemical modulators for lipid accumulation in Schizochytrium sp. S31

Schizochytrium sp. is a promising candidate for docosahexaenoic acid (DHA) production due to its high content of lipid and DHA proportions. To further enhance the lipid accumulation, seven chemical modulators were screened to evaluate their roles on lipid accumulation. Notably, among the seven tested chemical modulators, the addition of naphthoxyacetic acid (BNOA) or jasmonic acid (JA) was able to increase the lipid accumulation of Schizochytrium sp. S31. In addition, the effects of BNOA and JA were demonstrated dose-dependent and time-dependent, achieving a highest increase in lipid content by 11.16% and 12.71% when 2.0 mg/L of BNOA or 20 mg/L of JA was added into culture at 48 h after inoculation, respectively. In addition, the combination of 2 mg/L BNOA and 20 mg/L JA further increased lipid accumulation up to 16.79%. These results provided valuable strategy on promoting the lipid accumulation and DHA production by chemical modulators in Schizochytrium sp. S31.