Advances in algal lipid metabolism and their use to improve oil content.

Microalgae are eukaryotic photosynthetic micro-organisms that convert CO2 into carbohydrates, lipids, and other valuable metabolites. They are considered promising chassis for the production of various bioproducts, including fatty acid-derived biofuels. However, algae-based biofuels are not yet commercially available, mainly because of their low yields and high production cost. Optimizing strains to improve lipid productivity using the principles of synthetic biology should help move forward. This necessitates developments in the following areas: (1) identification of molecular bricks (enzymes, transcription factors, regulatory proteins etc.); (2) development of genetic tools; and (3) availability of high-throughput phenotyping methods. Here, we highlight the most recent developments in some of these areas and provide examples of the use of genome editing tools to improve oil content.

The Phytophthora parasitica effector AVH195 interacts with ATG8, attenuates host autophagy, and promotes biotrophic infection.

BACKGROUND: Plant pathogens secrete effector proteins into host cells to suppress immune responses and manipulate fundamental cellular processes. One of these processes is autophagy, an essential recycling mechanism in eukaryotic cells that coordinates the turnover of cellular components and contributes to the decision on cell death or survival. RESULTS: We report the characterization of AVH195, an effector from the broad-spectrum oomycete plant pathogen, Phytophthora parasitica. We show that P. parasitica expresses AVH195 during the biotrophic phase of plant infection, i.e., the initial phase in which host cells are maintained alive. In tobacco, the effector prevents the initiation of cell death, which is caused by two pathogen-derived effectors and the proapoptotic BAX protein. AVH195 associates with the plant vacuolar membrane system and interacts with Autophagy-related protein 8 (ATG8) isoforms/paralogs. When expressed in cells from the green alga, Chlamydomonas reinhardtii, the effector delays vacuolar fusion and cargo turnover upon stimulation of autophagy, but does not affect algal viability. In Arabidopsis thaliana, AVH195 delays the turnover of ATG8 from endomembranes and promotes plant susceptibility to P. parasitica and the obligate biotrophic oomycete pathogen Hyaloperonospora arabidopsidis. CONCLUSIONS: Taken together, our observations suggest that AVH195 targets ATG8 to attenuate autophagy and prevent associated host cell death, thereby favoring biotrophy during the early stages of the infection process.

Engineering Co-N-Cr Cross-Interfacial Electron Bridges to Break Activity-Stability Trade-Off for Superdurable Bifunctional Single Atom Oxygen Electrocatalysts.

Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts have exhibited encouraging oxygen reduction reaction (ORR) activity. Nevertheless, the insufficient long-term stability remains a widespread concern owing to the inevitable 2-electron byproducts, H2O2. Here, we construct Co-N-Cr cross-interfacial electron bridges (CIEBs) via the interfacial electronic coupling between Cr2O3 and Co-N-C, breaking the activity-stability trade-off. The partially occupied Cr 3d-orbitals of Co-N-Cr CIEBs induce the electron rearrangement of CoN4 sites, lowering the Co-OOH* antibonding orbital occupancy and accelerating the adsorption of intermediates. Consequently, the Co-N-Cr CIEBs suppress the two-electron ORR process and approach the apex of Sabatier volcano plot for four-electron pathway simultaneously. As a proof-of-concept, the Co-N-Cr CIEBs is synthesized by the molten salt template method, exhibiting dominant 4-electron selectively and extremely low H2O2 yield confirmed by Damjanovic kinetic analysis. The Co-N-Cr CIEBs demonstrates impressive bifunctional oxygen catalytic activity (▵E=0.70 V) and breakthrough durability including 100 % current retention after 10 h continuous operation and cycling performance over 1500 h for Zn-air battery. The hybrid interfacial configuration and the understanding of the electronic coupling mechanism reported here could shed new light on the design of superdurable M-N-C catalysts.

Correction: Mao et al. Gut Bacterial Community Determines the Therapeutic Effect of Ginsenoside on Canine Inflammatory Bowel Disease by Modulating the Colonic Mucosal Barrier. Microorganisms 2023, 11, 2616.

The authors wish to make the following corrections to this paper [...].

Gut Bacterial Community Determines the Therapeutic Effect of Ginsenoside on Canine Inflammatory Bowel Disease by Modulating the Colonic Mucosal Barrier.

Inflammatory bowel disease (IBD) comprises systemic inflammatory conditions primarily affecting the gastrointestinal tract, including Crohn's disease and ulcerative colitis. This research aims to analyze the clinical symptoms and pathogenesis of a Dextran sodium sulfate (DSS)-induced canine IBD model and evaluate the restorative effect of ginsenoside from a pathogenesis perspective. We established the DSS-induced canine IBD model and studied the pathological mechanisms. Additionally, we examined the therapeutic effect of ginsenosides by assessing the Canine Inflammatory Bowel Disease Activity Index (CIBDAI), C-reactive protein (CRP) levels, colonic tissue morphology, protein expression, and mucosal bacterial community analysis. Our findings revealed a total ginsenoside content of 22.7% in the ginsenoside extract. Animal experiments demonstrated that dogs with IBD exhibited decreased mental state, significantly increased CIBDAI and CRP levels, disrupted colonic epithelial tissue structure, decreased expression of mucin, tight junctions, and adherens junctions, as well as reduced diversity of the colonic mucosal bacterial community. Furthermore, correlation analysis highlighted a total of 38 bacterial strains correlated with physiological indices. Significantly, ginsenoside treatment could improve these symptoms and reverse the relative abundance of some bacterial communities. In conclusion, alterations in the properties of the colonic mucus layer or the reduction in MUC2, its core component, in dogs with IBD can lead to bacterial penetration of the mucus layer and subsequent contact with intestinal epithelial cells, resulting in inflammation. Remarkably, ginsenoside intervention showcased the capacity to positively influence the relative abundance of bacteria and impact the colonic mucus layer properties, thereby offering promising prospects for IBD management and recovery.

Overexpression of a MYB1 Transcription Factor Enhances Triacylglycerol and Starch Accumulation and Biomass Production in the Green Microalga Chlamydomonas reinhardtii.

Microalgae are promising platforms for biofuel production. Transcription factors (TFs) are emerging as key regulators of lipid metabolism for biofuel production in microalgae. We previously identified a novel TF MYB1, which mediates lipid accumulation in the green microalga Chlamydomonas under nitrogen depletion. However, the function of MYB1 on lipid metabolism in microalgae under standard growth conditions remains poorly understood. Here, we examined the effects of MYB1 overexpression (MYB1-OE) on lipid metabolism and physiological changes in Chlamydomonas. Under standard growth conditions, MYB1-OE transformants accumulated 1.9 to 3.2-fold more triacylglycerols (TAGs) than that in the parental line (PL), and total fatty acids (FAs) also significantly increased. Moreover, saturated FA (C16:0) was enriched in TAGs and total FAs in MYB1-OE transformants. Notably, starch and protein content and biomass production also significantly increased in MYB1-OE transformants compared with that in PL. Furthermore, RT-qPCR results showed that the expressions of key genes involved in TAG, FA, and starch biosynthesis were upregulated. In addition, MYB1-OE transformants showed higher biomass production without a compromised cell growth rate and photosynthetic activity. Overall, our results indicate that MYB1 overexpression not only enhanced lipid content but also improved starch and protein content and biomass production under standard growth conditions. TF MYB1 engineering is a promising genetic engineering tool for biofuel production in microalgae.

Constructing FeS and ZnS Heterojunction on N,S-Codoped Carbon as Robust Electrocatalyst toward Oxygen Reduction Reaction.

Highly active and cost-efficient electrocatalysts for oxygen reduction reaction (ORR) are significant for developing renewable energy conversion devices. Herein, a nanocomposite Fe/ZnS-SNC electrocatalyst with an FeS and ZnS heterojunction on N,S-codoped carbon has been fabricated via a facile one-step sulfonating of the pre-designed Zn- and Fe-organic frameworks. Benefitting from the electron transfer from FeS to adjacent ZnS at the heterointerfaces, the optimized Fe/ZnS-SNC900 catalyst exhibits excellent ORR performances, featuring the half-wave potentials of 0.94 V and 0.81 V in alkaline and acidic media, respectively, which is competitive with the commercial 20 wt.% Pt/C (0.87 and 0.76 V). The flexible Zn-air battery equipping Fe/ZnS-SNC900 affords a higher open-circuit voltage (1.45 V) and power density of 30.2 mW cm-2. Fuel cells assembled with Fe/ZnS-SNC900 as cathodic catalysts deliver a higher power output of 388.3 and 242.8 mW cm-2 in H2-O2 and -air conditions. This work proposes advanced heterostructured ORR electrocatalysts that effectively promote renewable energy conversions.

Enhancement of arsenic uptake and accumulation in green microalga Chlamydomonas reinhardtii through heterologous expression of the phosphate transporter DsPht1.

Arsenate (AsV) is a predominant arsenic contaminant in aerobic water. Microalgae have been recently used in the phytoremediation of arsenic-contaminated water. However, the amount of AsV uptake in microalgae is limited, which hinders the application of microalgae in arsenic-contaminated water treatment. Here, we found that the expression of a novel phosphate transporter DsPht1 in Dunaliella salina was highly upregulated after AsV exposure. Fluorescent protein-tagging analysis showed the plasma membrane location of DsPht1. Furthermore, DsPht1 was overexpressed in a model microalga Chlamydomonas reinhardtii. The DsPht1 transgenetic lines accumulated up to 6.4-fold higher total arsenic than the untransformed line, and the AsV amount in total arsenic increased by 8.3-fold. Moreover, the organoarsenic content was also higher in the transgenetic lines. Overall, the DsPht1 transformants generated in this study increased arsenate uptake and transformation, which are promising for the effective phytoremediation of arsenic-contaminated water.

Dual-Site W-O-CoP Catalysts for Active and Selective Nitrate Conversion to Ammonia in a Broad Concentration Window.

Environmentally friendly electrochemical reduction of contaminated nitrate to ammonia (NO3 - RR) is a promising solution for large quantity ammonia (NH3 ) production, which, however, is a complex multi-reaction process involving coordination between different reaction intermediates of nitrate reduction and water decomposition-provided active hydrogen (Hads ) species. Here, a dual-site catalyst of [W-O] group-doped CoP nanosheets (0.6W-O-CoP@NF) has been designed to synergistically catalyze the NO3 - RR and water decomposition, especially the reactions between the intermediates of NO3 - RR and water decomposition-provided Hads species. This catalytic NO3 - RR exhibits an extremely high NH3 yield of 80.92 mg h-1 cm-2 and a Faradaic efficiency (FE) of 95.2% in 1 m KOH containing 0.1 m NO3 - . Significantly, 0.6W-O-CoP@NF presents greatly enhanced NH3 yield and FE in a wide NO3 - concentration ranges of 0.001-0.1 m compared to the reported. The excellent NO3 - RR performance is attributed to a synergistic catalytic effect between [W-O] and CoP active sites, in which the doped [W-O] group promotes the water decomposition to supply abundant Hads , and meanwhile modulates the electronic structure of Co for strengthened adsorption of Hads and the hydrogen (H2 ) release prevention, resultantly facilitating the NO3 - RR. Finally, a Zn-NO3 - battery has been assembled to simultaneously achieve three functions: electricity output, ammonia production, and nitrate treatment in wastewater.

Active site recovery and N-N bond breakage during hydrazine oxidation boosting the electrochemical hydrogen production.

Substituting hydrazine oxidation reaction for oxygen evolution reaction can result in greatly reduced energy consumption for hydrogen production, however, the mechanism and the electrochemical utilization rate of hydrazine oxidation reaction remain ambiguous. Herein, a bimetallic and hetero-structured phosphide catalyst has been fabricated to catalyze both hydrazine oxidation and hydrogen evolution reactions, and a new reaction path of nitrogen-nitrogen single bond breakage has been proposed and confirmed in hydrazine oxidation reaction. The high electro-catalytic performance is attributed to the instantaneous recovery of metal phosphide active site by hydrazine and the lowered energy barrier, which enable the constructed electrolyzer using bimetallic phosphide catalyst at both sides to reach 500 mA cm-2 for hydrogen production at 0.498 V, and offer an enhanced hydrazine electrochemical utilization rate of 93%. Such an electrolyzer can be powered by a bimetallic phosphide anode-equipped direct hydrazine fuel cell, achieving self-powered hydrogen production at a rate of 19.6 mol h-1 m-2.

Enhanced triacyclglycerols and starch synthesis in Chlamydomonas stimulated by the engineered biodegradable nanoparticles.

Microalgae are promising feedstock for renewable fuels. The accumulation of oils in microalgae can be enhanced by nanoparticle exposure. However, the nanoparticles employed in previous studies are mostly non-biodegradable, which hinders nanoparticles developing as promising approach for biofuel production. We recently reported the engineered resin nanoparticles (iBCA-NPs), which were found to be biodegradable in this study. When the cells of green microalga Chlamydomonas reinhardtii were exposed to the iBCA-NPs for 1 h, the cellular triacyclglycerols (TAG) and starch contents increased by 520% and 60% than that in the control. The TAG production improved by 1.8-fold compared to the control without compromised starch production. Additionally, the content of total fatty acids increased by 1.3-fold than that in control. Furthermore, we found that the iBCA-NPs addition resulted in increased cellular reactive oxygen species (ROS) content and upregulated the activities of antioxidant enzymes. The relative expressions of the key genes involved in TAG and starch biosynthesis were also upregulated. Overall, our results showed that short exposure of the iBCA-NPs dramatically enhances TAG and starch accumulation in Chlamydomonas, which probably resulted from prompt upregulated expression of the key genes in lipid and starch metabolic pathways that were triggered by over-accumulated ROS. This study reported a useful approach to enhance energy-rich reserve accumulation in microalgae. KEY POINTS: 1. The first attempt to increase oil and starch in microalgae by biodegradable NPs. 2. The biodegradability of iBCA-NPs by the BOD test was more than 50% after 28 days. 3. The iBCA-NPs induce more energy reserves than that of previously reported NPs.

Co-Expression of Lipid Transporters Simultaneously Enhances Oil and Starch Accumulation in the Green Microalga Chlamydomonas reinhardtii under Nitrogen Starvation.

Lipid transporters synergistically contribute to oil accumulation under normal conditions in microalgae; however, their effects on lipid metabolism under stress conditions are unknown. Here, we examined the effect of the co-expression of lipid transporters, fatty acid transporters, (FAX1 and FAX2) and ABC transporter (ABCA2) on lipid metabolism and physiological changes in the green microalga Chlamydomonas under nitrogen (N) starvation. The results showed that the TAG content in FAX1-FAX2-ABCA2 over-expressor (OE) was 2.4-fold greater than in the parental line. Notably, in FAX1-FAX2-ABCA2-OE, the major membrane lipids and the starch and cellular biomass content also significantly increased compared with the control lines. Moreover, the expression levels of genes directly involved in TAG, fatty acid, and starch biosynthesis were upregulated. FAX1-FAX2-ABCA2-OE showed altered photosynthesis activity and increased ROS levels during nitrogen (N) deprivation. Our results indicated that FAX1-FAX2-ABCA2 overexpression not only enhanced cellular lipids but also improved starch and biomass contents under N starvation through modulation of lipid and starch metabolism and changes in photosynthesis activity. The strategy developed here could also be applied to other microalgae to produce FA-derived energy-rich and value-added compounds.

The long overlooked microalgal nitrous oxide emission: Characteristics, mechanisms, and influencing factors in microalgae-based wastewater treatment scenarios.

Microalgae-based wastewater treatment is particularly advantageous in simultaneous CO2 sequestration and nutrients recovery, and has received increasing recognition and attention in the global context of synergistic pollutants and carbon reduction. However, the fact that microalgae themselves can generate the potent greenhouse gas nitrous oxide (N2O) has been long overlooked, most previous research mainly regarded microalgae as labile organic carbon source or oxygenic approach that interfere bacterial nitrification-denitrification and the concomitant N2O production. This study, therefore, summarized the amount and rate of N2O emission in microalgae-based systems, interpreted in-depth the multiple pathways that lead to NO formation as the key precursor of N2O, and the pathways that transform NO into N2O. Reduction of nitrite could take place in either the cytoplasm or the mitochondria to form NO by a series of enzymes, while the NO could be enzymatically reduced to N2O at the chloroplasts or the mitochondria respectively under light and dark conditions. The influences of abiotic factors on microalgal N2O emission were analyzed, including nitrogen types and concentrations that directly affect the nitrogen transformation routes, illumination and oxygen conditions that regulate the enzymatic activities related to N2O generation, and other factors that indirectly interfere N2O emission via NO regulation. The uncertainty of microalgae-based N2O emission in wastewater treatment scenarios were emphasized, which would be particularly impacted by the complex competition between microalgae and ammonia oxidizing bacteria or nitrite oxidizing bacteria over ammonium or inorganic carbon source. Future studies should put more efforts in improving the compatibility of N2O emission results expressions, and adopting consistent NO detection methods for N2O emission prediction. This review will provide much valuable information on the characteristics and mechanisms of microalgal N2O emission, and arouse more attention to the non-negligible N2O emission that may impair overall greenhouse gas reduction efficiency in microalgae-based wastewater treatment systems.

CoW Bimetallic Carbide Nanocatalysts: Computational Exploration, Confined Disassembly-Assembly Synthesis and Alkaline/Seawater Hydrogen Evolution.

Earth-abundant tungsten carbide exhibits potential hydrogen evolution reaction (HER) catalytic activity owing to its Pt-like d-band electronic structure, which, unfortunately, suffers from the relatively strong tungsten-hydrogen binding, deteriorating its HER performance. Herein, a catalyst design concept of incorporating late transition metal into early transition metal carbide is proposed for regulating the metal-H bonding strength and largely enhancing the HER performance, which is employed to synthesize CoW bi-metallic carbide Co6 W6 C by a "disassembly-assembly" approach in a confined environment. Such synthesized Co6 W6 C nanocatalyst features the optimal Gibbs free energy of *H intermediate and dissociation barrier energy of H2 O molecules as well by taking advantage of the electron complementary effect between Co and W species, which endows the electrocatalyst with excellent HER performance in both alkaline and seawater/alkaline electrolytes featuring especially low overpotentials, elevated current densities, and much-enhanced operation durability in comparison to commercial Pt/C catalyst. Moreover, a proof-of-concept Mg/seawater battery equipped with Co6 W6 C-2-600 as cathode offers a peak power density of 9.1 mW cm-2 and an open-circuit voltage of ≈1.71 V, concurrently realizing hydrogen production and electricity output.

A smart and precise mixing strategy for efficient and cost-effective microalgae production in open ponds.

Microalgae biotechnology is a great candidate for carbon neutralization, wastewater treatment and the sustainable production of biofuels and food. Efficient and cost-effective microalgae production depends on highly coordinating the resources used for algal growth. However, dynamic natural disturbances such as culture temperature and sunlight can lead to the poor coordination and waste of resources. Open ponds are the most commonly used commercial microalgal production systems, and enhanced mixing can significantly increase their productivity, but mixing energy can be seriously wasted due to dynamic disturbances, presenting a hindrance to further reducing production costs. Herein, a smart and precise mixing strategy was developed for open ponds in which a paddle wheel's stirring speed for an open pond was smartly and precisely controlled in real time based on dynamic variations in light intensity and culture temperature. The proposed technology achieved the same biomass productivity of Spirulina platensis (8.37 g m-2 day-1) as a control with a constant high mixing rate under dynamic disturbances while reducing mixing energy inputs by approximately 30 % compared to the control. This study provides a promising method to address serious resource waste and poor coordination due to dynamic natural disturbances, holding great potential for efficient and cost-effective microalgae production.

Fe2+ /Fe3+ Cycling for Coupling Self-Powered Hydrogen Evolution and Preparation of Electrode Catalysts.

A novel Zn-Fe flow battery featuring an Fe3+ reduction reaction (Fe3+ RR)-coupled zinc oxidation, and an Fe2+ oxidation reaction (Fe2+ OR)-coupled hydrogen evolution reaction (HER) system as well, was established. This battery is capable of driving two Fe2+ OR-coupled HER systems in series based on the above Fe2+ /Fe3+ cycling, for efficient self-powered hydrogen evolution. Meanwhile, this Fe2+ /Fe3+ cycling enables the preparation of a multifunctional catalyst, Pt-3@SXNS (siloxene nanosheet), by the Fe2+ OR-promoted dispersion of Pt nanoparticles on SXNS; alternatively, this support could be obtained by Fe3+ RR-assisted exfoliation using Fe3+ from the anolyte of Fe2+ OR-coupled HER. The Pt-3@SXNS catalyst exhibits excellent catalytic activities toward Fe3+ RR in the Zn-Fe flow battery, HER, and Fe2+ OR in the electrolyzer, which is attributed to the strong electronic interaction between Pt and Si. This work offers a new strategy for energy storage and low-cost hydrogen production from acidic wastewater.

Enhanced accumulation of oil through co-expression of fatty acid and ABC transporters in Chlamydomonas under standard growth conditions.

BACKGROUND: Chloroplast and endoplasmic reticulum (ER)-localized fatty acid (FA) transporters have been reported to play important roles in oil (mainly triacylglycerols, TAG) biosynthesis. However, whether these FA transporters synergistically contribute to lipid accumulation, and their effect on lipid metabolism in microalgae are unknown. RESULTS: Here, we co-overexpressed two chloroplast-localized FA exporters (FAX1 and FAX2) and one ER-localized FA transporter (ABCA2) in Chlamydomonas. Under standard growth conditions, FAX1/FAX2/ABCA2 over-expression lines (OE) accumulated up to twofold more TAG than the parental strain UVM4, and the total amounts of major polyunsaturated FAs (PUFA) in TAG increased by 4.7-fold. In parallel, the total FA contents and major membrane lipids in FAX1/FAX2/ABCA2-OE also significantly increased compared with those in the control lines. Additionally, the total accumulation contribution ratio of PUFA, to total FA and TAG synthesis in FAX1/FAX2/ABCA2-OE, was 54% and 40% higher than that in UVM4, respectively. Consistently, the expression levels of genes directly involved in TAG synthesis, such as type-II diacylglycerol acyltransferases (DGTT1, DGTT3 and DGTT5), and phospholipid:diacylglycerol acyltransferase 1 (PDAT1), significantly increased, and the expression of PGD1 (MGDG-specific lipase) was upregulated in FAX1/FAX2/ABCA2-OE compared to UVM4. CONCLUSION: These results indicate that the increased expression of FAX1/FAX2/ABCA2 has an additive effect on enhancing TAG, total FA and membrane lipid accumulation and accelerates the PUFA remobilization from membrane lipids to TAG by fine-tuning the key genes involved in lipid metabolism under standard growth conditions. Overall, FAX1/FAX2/ABCA2-OE shows better traits for lipid accumulation than the parental line and previously reported individual FA transporter-OE. Our study provides a potential useful strategy to increase the production of FA-derived energy-rich and value-added compounds in microalgae.

Differences in Glycerolipid Response of Chlamydomonas reinhardtii Starchless Mutant to High Light and Nitrogen Deprivation Stress Under Three Carbon Supply Regimes.

Carbon source serves as a crucial factor for microalgal lipid biosynthesis. The supplied exogenous inorganic or organic carbon affects lipid accumulation in microalgae under stress conditions. However, the impacts of different carbon availability on glycerolipid metabolism, triacylglycerol (TAG) metabolism in particular, still remain elusive in microalgae. Chlamydomonas starchless mutant BAFJ5 has emerged as a model system to study TAG metabolism, due to its property of hyper-accumulating TAG. In this study, the glycerolipidomic response of the starchless BAFJ5 to high light and nitrogen-deprived (HL-N) stress was deciphered in detail to distinguish glycerolipid metabolism under three carbon supply regimes. The results revealed that the autotrophically and mixotrophically grown BAFJ5 cells aerated with air containing 2% CO2 presented similar changes in growth, photosynthetic activity, biochemical components, and glycerolipid metabolism under HL-N conditions. But the mixotrophically grown BAFJ5 aerated with air containing 0.04% CO2 exhibited more superior accumulation in TAG, which was esterified with a significantly higher proportion of C18:1n9 and prominently the lower proportions of polyunsaturated fatty acids. In addition, these cells increased the relative levels of C18:2n6 in the membrane lipids, i.e., monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), in priority, and decreased that of C18:3n3 and C18:4n3 in the betaine lipid, N,N,N-trimethylhomoserine diacylglycerol (DGTS), subsequently, to adapt to the HL-N stress conditions, compared to the cells under the other two conditions. Thus, it was suggested that C. reinhardtii starchless mutant appeared to present distinct metabolism for TAG biosynthesis involving membrane lipid remodeling under distinct carbon supply regimes. This study provides insights into how the different carbon supply regimes affect lipid metabolism in Chlamydomonas starchless cells, which will benefit the optimized production of storage lipids in microalgae.

The Chlamydomonas transcription factor MYB1 mediates lipid accumulation under nitrogen depletion.

Microalgae accumulate high levels of oil under stress, but the underlying biosynthetic pathways are not fully understood. We sought to identify key regulators of lipid metabolism under stress conditions. We found that the Chlamydomonas reinhardtii gene encoding the MYB-type transcription factor MYB1 is highly induced under stress conditions. Two myb1 mutants accumulated less total fatty acids and storage lipids than their parental strain upon nitrogen (N) depletion. Transcriptome analysis revealed that genes involved in lipid metabolism are highly enriched in the wild-type but not in the myb1-1 mutant after 4 h of N depletion. Among these genes were several involved in the transport of fatty acids from the chloroplast to the endoplasmic reticulum (ER): acyl-ACP thioesterase (FAT1), Fatty Acid EXporters (FAX1, FAX2), and long-chain acyl-CoA synthetase1 (LACS1). Furthermore, overexpression of FAT1 in the chloroplast increased lipid production. These results suggest that, upon N depletion, MYB1 promotes lipid accumulation by facilitating fatty acid transport from the chloroplast to the ER. This study identifies MYB1 as an important positive regulator of lipid accumulation in C. reinhardtii upon N depletion, adding another player to the established regulators of this process, including NITROGEN RESPONSE REGULATOR 1 (NRR1) and TRIACYLGLYCEROL ACCUMULATION REGULATOR 1 (TAR1).

[Tactic movement of microalgae and its application in targeted transport: a review].

Microalgae are a group of photosynthetic microorganisms, which have the general characteristics of plants such as photosynthesis, and some species have the ability of movement which resembles animals. Recently, it was reported that microalgae cells can be engineered to precisely deliver medicine-particles and other goods in microfluidic chips. These studies showed great application potential in biomedical treatment and pharmacodynamic analysis, which have become one of the current research hotspots. However, these developments have been rarely reviewed. Here, we summarized the advances in manageable movement exemplified by a model microalgae Chlamydomonas reinhardtii based on its characteristics of chemotaxis, phototaxis, and magnetotaxis. The bottlenecks and prospects in the application of microalgae-based tactic movement were also discussed. This review might be useful for rational design and modification of microalgal manageable movement to achieve targeted transport in medical and other fields.