Photosynthetic Microalgae Research Articles

Unlocking the adaptation mechanisms of the oleaginous microalga Scenedesmus sp. BHU1 under elevated salt stress: a physiochemical, lipidomics and transcriptomics approach.

Microalgae are vital for their photosynthetic abilities, contributing significantly to global oxygen production, serving as a key trophic level in aquatic ecosystems, aiding in biofuel production, assisting in wastewater treatment, and facilitating the synthesis of valuable biochemicals. Despite these advantages, photosynthetic microalgae are sensitive to salt stress, which alters their physiochemical and metabolic status, ultimately reducing microalgal growth. This sensitivity highlights the importance of understanding the impact of elevated salt content on the physiochemical, metabolic, and transcriptomic profiling of Scenedesmus sp., areas that are not yet fully understood. Our findings indicate that elevated salt stress decreases photosynthetic efficiency and increases non-regulated photochemical quenching of photosystem II (PSII). Moreover, PSII-driven linear electron flow (LEF) decreased, whereas photosystem I (PSI)-driven cyclic electron flow (CEF) increased in salt-stressed cells. To better understand the electron flow from PSII to PSI under elevated salt treatment, we analyzed the excitation energy flux per reaction center (RC), per cross-section (CS), energy flux ratios, and the potential index of PSII. Additionally, flow cytometry graphs depict the viability assay of Scenedesmus sp. BHU1. Our observations further revealed an increase in biochemical attributes, such as stress biomarkers, osmoprotectants, and enzymatic antioxidants, which help scavenge reactive oxygen species (ROS) under salt stress. Intracellular cations (Na + and Ca2+) were increased, while K+ levels decreased, indicating mechanisms of cellular homeostasis under salt stress. UHPLC-HRMS-based lipidome analysis confirmed that increasing salt stress induces the hyperaccumulation of several fatty acids involved in adaptation. Moreover, transcriptome analysis revealed the upregulation of genes associated with PSI, glycolysis, starch metabolism, sucrose metabolism, and lipid accumulation under salt stress. In contrast, genes related to PSII and C3 carbon fixation were downregulated to mitigate the adverse effects of salt stress.

Oxygenation by Intravascular Photosynthesis Reduces Kidney Damage During ex Vivo Preservation.

Several clinical issues are associated with reduced oxygen delivery to tissues due to impaired vascular perfusion; moreover, organs procured for transplantation are subjected to severe hypoxia during preservation. Consequently, alternative tissue oxygenation is an active field in biomedical research where several innovative approaches have been recently proposed. Among these, intravascular photosynthesis represents a promising approach as it relies on the intrinsic capacity of certain microorganisms to produce oxygen upon illumination. In this context, this work aims at the development of photosynthetic perfusable solutions that could be applied to preserve organs for transplantation purposes. Our findings demonstrate that a biocompatible physiological solution containing the photosynthetic microalgae Chlamydomonas reinhardtii can fulfill the metabolic oxygen demand of rat kidney slices in vitro. Furthermore, intravascular administration of this solution does not induce tissue damage in the rat kidneys. Moreover, kidney slices obtained from these algae-perfused organs exhibited significantly improved preservation after 24 h of incubation in hypoxia while exposed to light, resulting in reduced tissue damage and enhanced metabolic status. Overall, the results presented here contribute to the development of alternative strategies for tissue oxygenation, supporting the use of perfusable photosynthetic solutions for organ preservation in transplantation.

Developing an off-site bicarbonation absorber system to promote microalgal fixation of CO2 in exhaust gas from biogas upgrading

In order to address the risk of explosion due to CH4 from exhaust gas produced during biogas upgrading in closed carbon fixation systems employing photosynthetic microalgae, an off-site bicarbonation absorber system was developed to promote microalgal CO2 fixation under atmospheric pressure. The abundant CO2 in the biogas upgrading exhaust gas (≥90 vol% CO2, ≤10 vol% CH4) reacted with a Na2CO3 solution in the off-site bicarbonation absorber to produce NaHCO3, which was used as carbon source for microalgal growth in enclosed column photobioreactors. After the reaction, CH4 was discharged outside the bicarbonation absorber because it did not react with the Na2CO3 solution and was extremely difficult to dissolve in water, thereby avoiding the explosion risk due to accumulated CH4 in the enclosed column photobioreactors. The experimental results showed that the Spirulina growth rate first increased 1.7 times, peaking at 0.6 g/L/d, and then decreased when the bicarbonation reaction time (optimal 50 min), absorber diameter (optimal 10 cm), initial Na2CO3 concentration (optimal 173 mM), and exhaust gas aeration rate (optimal 100 sccm) increased. The optimal molar ratio of NaHCO3 to total inorganic carbon in the bicarbonation absorber solution reached 79 %. The sufficient HCO3- supply and suitable pH of the microalgal solution improved the synthesis of photosynthetic pigments in the microalgal cells and enhanced their photochemical efficiency and carbon sequestration rates.

Diatoms in Focus: Chemically Doped Biosilica for Customized Nanomaterials.

Diatoms are photosynthetic microalgae widely diffused around the globe and well adapted to thrive in diverse environments. Their success is closely related to the nanostructured biosilica shell (frustule) that serves as exoskeleton. Said structures have attracted great attention, thanks to their hierarchically ordered network of micro- and nanopores. Frustules display high specific surface, mechanical resistance and photonic properties, useful for the design of functional and complex materials, with applications including sensing, biomedicine, optoelectronics and energy storage and conversion. Current technology allows to alter the chemical composition of extracted frustules with a diverse array of elements, via chemical and biochemical strategies, without compromising their valuable morphology. We started our research on diatoms from the viewpoint of material scientists, envisaging the possibilities of these nanostructured silica shells as a general platform to obtain functional materials for several applications via chemical functionalization. Our first paper in the field was published in ChemPlusChem ten years ago. Ten years later, in this Perspective, we gather the most recent and relevant functional materials derived from diatom biosilica to show the growth and diversification that this field is currently experiencing, and the key role it will play in the near future.

In Vivo Lifetime Imaging of the Internal O2 Dynamics in Corals with near-Infrared-Emitting Sensor Nanoparticles.

Mapping of O2 with luminescent sensors within intact animals is challenging due to attenuation of excitation and emission light caused by tissue absorption and scattering as well as interfering background fluorescence. Here we show the application of luminescent O2 sensor nanoparticles (∼50-70 nm) composed of the O2 indicator platinum(II) tetra(4-fluoro)phenyltetrabenzoporphyrin (PtTPTBPF) immobilized in poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA). We injected the sensor nanoparticles into the gastrovascular system of intact colony fractions of reef-building tropical corals that harbor photosynthetic microalgae in their tissues. The sensor nanoparticles are excited by red LED light (617 nm) and emit in the near-infrared (780 nm), which enhances the transmission of excitation and emission light through biological materials. This enabled us to map the internal O2 concentration via time-domain luminescence lifetime imaging through the outer tissue layers across several coral polyps in flowing seawater. After injection, nanoparticles dispersed within the coral tissue for several hours. While luminescence intensity imaging showed some local aggregation of sensor particles, lifetime imaging showed a more homogeneous O2 distribution across a larger area of the coral colony. Local stimulation of symbiont photosynthesis in corals induced oxygenation of illuminated tissue areas and formation of lateral O2 gradients toward surrounding respiring tissues, which were dissipated rapidly after the onset of darkness. Such measurements are key to improving our understanding of how corals regulate their internal chemical microenvironment and metabolic activity, and how they are affected by environmental stress such as ocean warming, acidification, and deoxygenation. Our experimental approach can also be adapted for in vivo O2 imaging in other natural systems such as biofilms, plant and animal tissues, as well as in organoids and other cell constructs, where imaging internal O2 conditions are relevant and challenging due to high optical density and background fluorescence.

Biosafety risks, control, and biocontainment of engineered microalgae

Microalgae, with the ability to harness solar energy to fix CO2 and convert it into organic compounds, have emerged as promising green cell factories. With the rapid development of cutting-edge biotechnologies, the research and application of photosynthetic microalgae have been expanding, leading to comprehensive and in-depth engineering of microalgae. The synthetic biology and genome editing technologies have enabled the applications of microalgae in medicine, agriculture, food, energy, and the environment. However, the survival and spreading of engineered microalgae in the natural environment pose potential safety risks to ecosystems and human health. To curb the risks caused by the spreading of engineered microalgae in the environment, biosafety policies should be formulated for engineered microalgae and the prevention and control technologies should be developed. Toward this goal, researchers have developed biocontainment systems, including positive strategies such as the design of toxic protein-based kill switches and passive strategies such as knocking out essential genes to construct the strains with nutritional deficiencies, thereby spatially containing engineered microalgae. This article summarizes the application of cutting-edge biotechnologies in the engineering of microalgae, the biosafety risks and management regulations associated with the escape of engineered microalgae, and the progress in novel biocontainment technologies established for engineered microalgae. Finally, this article gives insights into the future development direction of microalgae biocontainment.

Toxicological effects, absorption and biodegradation of bisphenols with different functional groups in Chromochloris zofingiensis

Bisphenols (BPs) are recognized as endocrine disrupting compounds and have garnered increasing attention due to their widespread utilization. However, the varying biological toxicities and underlying mechanisms of BPs with different functional groups remain unknown. In the present study, the toxic effects of four BPs (BPA, BPS, BPAF, and TBBPA) on a photosynthetic microalgae Chromochloris zofingiensis were compared. Results showed that halogen-containing BPs exhibited higher cellular uptake, leading to more severe oxidative stress, lower photosynthetic efficiency, and greater accumulation of starch and lipids. Specifically, TBBPA with bromine groups showed a greater toxicity than BPAF with fluorine groups, possibly due to the incomplete debromination in C. zofingiensis. Transcriptomic analysis revealed that halogen-containing BPs triggered greater number of differentially expressed genes (DEGs), and only 64 common DEGs were found among different BPs, indicating that the effects of BPs with different functional groups varied greatly. Genes involved in endocytosis, peroxisomes, and endoplasmic reticulum protein processing pathways were mostly upregulated across different BPs, while photosynthesis-related genes showed varied expression, possibly due to their distinct functional groups. Additionally, SIN3A, ZFP36L, CHMP, and ATF2 emerged as potential key regulatory genes. Overall, this study thoroughly explained how functional groups impact the toxicity and biodegradation of BPs in C. zofingiensis.

Generation of photosynthetic biomaterials by loading electrospun fibres with the green microalgae, Chlamydomonas reinhardtii

Hypoxic environments within tissues, characterised by low concentrations of oxygen, are a major limitation in certain biomedical applications such as wound healing and tissue engineering. Electrospun fibrous mats have demonstrated potential for use in these applications as they can absorb fluids and physically protect tissues, can be loaded with active compounds (i.e., antimicrobial or therapeutics) and have been shown to support cell migration, adhesive and proliferation. Here, we report electrospun fibrous mats which have been functionalised to overcome the limitations of hypoxia. Specifically, the successful incorporation of the photosynthetic green microalgae Chlamydomonas reinhardtii into electrospun fibrous mats based on polycaprolactone, polylactic acid, and cellulose acetate is demonstrated for the first time. The exploration of various culture conditions found that maximal C. reinhardtii growth occurred under constant light exposure over 24 h at 26 °C. Once laden with C. reinhardtii, the monitoring of material health found that the biomaterials developed were photosynthetically active over a period of 7 days, and capable of generating high concentrations of oxygen to the local environment. Overall, the findings reported here present C. reinhardtii-laden electrospun mats as strong candidates for oxygen-generating materials for potential use in biomedical applications.

Kombucha–Chlorella–Proteinoid Biosynthetic Classifiers of Audio Signals

ABSTRACTThis paper describes the development of a bioinspired composite material capable of audio classification applications. Hydrogel matrices produced by microorganisms combined with synthetic biology elements, allow for the development of adaptable bioelectronics that connect biology and technology in a customized way. In this study, a composite population of kombucha, chlorella, and proteinoids (thermal proteins) is utilized to respond to acoustic signals converted to electrical waveforms. The kombucha zoogleal mats, which are made and populated by over 60 species of yeasts and bacteria, offer a matrix at the micro level that is connected to the photosynthetic microalgae chlorella. Proteinoids formed through thermal condensation exhibit unique patterns of signaling kinetics. This living material has the ability to be electrically stimulated and can process signals in a way feasible for sensory applications. Using English alphabet audio inputs, a systematic analysis demonstrates the capability to differentiate audio waveforms based solely on biological composite responses. The use of spectral analysis allows for the identification of specific spike timing patterns that encode unique characteristics of individual letters. Moreover, network disturbances result in specific changes in output, so validating the ability to adjust waveform classification. The study demonstrates that kombucha–chlorella–proteinoid composites provide a durable and versatile bioelectronic platform for immediate auditory processing. The work represents progress toward the development of bioelectronic systems that can be customized based on the principles of biological sensory processing, cognition, and adaptation.

Quantitative proteomics insights into Chlamydomonas reinhardtii thermal tolerance enhancement by a mutualistic interaction with Sinorhizobium meliloti.

Photosynthetic microalgae are key primary producers in aquatic ecosystems, playing an important role in the global carbon cycle. Nearly every alga lives in association with a diverse community of microorganisms that influence each other and their metabolic activities or survival. One chemical produced by bacteria that influence algae is vitamin B12, an enzyme cofactor used for a variety of metabolic functions. The alga Chlamydomonas reinhardtii benefits from vitamin B12 produced by Sinorhizobium meliloti by producing the amino acid methionine under high temperatures which are required for Chlamydomonas thermotolerance. Yet, our understanding of this interaction under normal and stressful temperatures is poor. Here, we used quantitative proteomics to identify differentially expressed proteins to reveal metabolic adjustments made by Chlamydomonas and Sinorhizobium that could facilitate this mutualism. These findings will enhance our understanding of how photosynthetic algae and their associated microbiomes will respond as global temperatures increase.

Extending the use of normal hemispherical transmittance ([formula omitted]) measurements by modeling 3D multiple scattering radiative transfer

Spectrophotometers or optical benches using integrating spheres to measure normal-hemispherical transmittance TNH are widespread laboratory equipments. Although it is known that they cannot be used for ”highly turbid” samples, because multiple scattering may lead transmitted radiation to miss the entrance of the integrating sphere, very little is generally known about their exact validity range. Here we present a method to characterize the validity range of any such spectrophotometer and observe that most of them fail to measure TNH for scattering optical thickness above 0.25 (i.e. for TNH<0.9 in the case of non absorbing media with g=0). We also show how it is possible to continue using spectrophotometers even outside their TNH measurement validity range, without any calibration, thanks to a proper simulation of radiative transfer and geometrical optics. We make available the corresponding radiative transfer simulation tools as open access codes, that have been developed for a straightforward implementation on a wide range of experimental setups. The method is validated on three different spectrophotometers or optical benches using standardized latex microspheres, then its practical implementation is illustrated in the case of semi-conductor particles and photosynthetic microalgae. Errors in analysis arising from the misuse of such optical devices are discussed throughout the article.

Application of Cyanobacteria as Chassis Cells in Synthetic Biology.

Synthetic biology is an exciting new area of research that combines science and engineering to design and build new biological functions and systems. Predictably, with the development of synthetic biology, more efficient and economical photosynthetic microalgae chassis will be successfully constructed, making it possible to break through laboratory research into large-scale industrial applications. The synthesis of a range of biochemicals has been demonstrated in cyanobacteria; however, low product titers are the biggest barrier to the commercialization of cyanobacterial biotechnology. This review summarizes the applied improvement strategies from the perspectives of cyanobacteria chassis cells and synthetic biology. The harvest advantages of cyanobacterial products and the latest progress in improving production strategies are discussed according to the product status. As cyanobacteria synthetic biology is still in its infancy, apart from the achievements made, the difficulties and challenges in the application and development of cyanobacteria genetic tool kits in biochemical synthesis, environmental monitoring, and remediation were assessed.

In situ activation of peroxymonosulfate with bioelectricity for sulfamethoxazole sustainable removal

Conventional electrochemical activation of peroxymonosulfate (PMS) is not very cost-effective and practical by the excessive input of energy. The electricity generated by photosynthetic microalgae fuel cells (MFCs) is utilized to activate PMS, which would achieve the combination of green bioelectricity and advanced oxidation processes for sustainable pollutants degradation. In this study, a novel dual-chamber of MFCs was constructed by using microalgae as anode electron donor and PMS as cathode electron acceptor, which was operating under both close-circuit and open-circuit conditions. Under close-circuit condition, 1–12 mM PMS in cathode was successfully in situ activated, where 32.00%–99.83% of SMX was removed within 24 h, which was about 1.21–1.78 times of that in the open-circuit of MFCs. Meanwhile, a significant increase in bioelectricity generation in MFCs was observed after the accumulation of microalgae biomass (4.65–5.37 mg/L), which was attributed to the efficient electron separation and transfer. Furthermore, the electrochemical analysis demonstrated that SMX or its products were functioned as electronic shuttles, facilitating the electrochemical reaction and altering the electrical capacitance. The quenching experiments and voltage output results reflected that complex active radical (SO4⋅-, ⋅OH, and 1O2) were involved in SMX removal. Seven degradation products of SMX were detected and S–N bond cleavage was the main degradation pathway. Predicted toxicity values calculated by ECOSAR program showed that all the products were less toxic or nontoxic. Finally, the density functional theory (DFT) calculations revealed that the O and N atoms on SMX were more susceptible to electrophilic reactions, which were more vulnerable to be attacked by reactive species. This study provided new insights into the activation of PMS by bioelectricity for SMX degradation, proposing the mechanisms for PMS activation and degradation sites of SMX.

CRISPR/Cas9-Mediated Knockout of the Lycopene ε-Cyclase for Efficient Astaxanthin Production in the Green Microalga Chlamydomonas reinhardtii.

Carotenoids are valuable pigments naturally occurring in all photosynthetic plants and microalgae as well as in selected fungi, bacteria, and archaea. Green microalgae developed a complex carotenoid profile suitable for efficient light harvesting and light protection and harbor great capacity for carotenoid production through the substantial power of the endogenous 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. Previous works established successful genome editing and induced significant changes in the cellular carotenoid content in Chlamydomonas reinhardtii. This study employs a tailored carotenoid pathway for engineered bioproduction of the valuable ketocarotenoid astaxanthin. Functional knockout of lycopene ε-cyclase (LCYE) and non-homologous end joining (NHEJ)-based integration of donor DNA at the target site inhibit the accumulation of α-carotene and consequently lutein and loroxanthin, abundant carotenoids in C. reinhardtii without changes in cellular fitness. PCR-based screening indicated that 4 of 96 regenerated candidate lines carried (partial) integrations of donor DNA and increased ß-carotene as well as derived carotenoid contents. Iterative overexpression of CrBKT, PacrtB, and CrCHYB resulted in a 2.3-fold increase in astaxanthin accumulation in mutant ΔLCYE#3 (1.8 mg/L) compared to the parental strain UVM4, which demonstrates the potential of genome editing for the design of a green cell factory for astaxanthin bioproduction.

Modelling dynamics of photosynthetic units and microalgae growth based on high throughput pulsed light screens

Light-dark cycles on the s timescale are typical of cell cycling through photobioreactors and high-rate ponds and can significantly impact microalgae cultivation efficiency. Here, a novel formulation of the Camacho-Rubio microalgae growth model was developed to simulate dynamic growth under pulsed light (s timescale). It simultaneously captures the dynamics of the photosynthetic units (PSUs: open, closed and photoinhibited) and their impact on biomass productivity over time. Theoretical knowledge of PSU mediated processes operating on characteristic timescales was used to identify intra- and inter-light cycle variable dynamics and guide the model formulation. For model calibration, dynamic profiles of microalgae growth under pulsed light in a High-Throughput Screening platform were employed, after Principal Component Analysis (PCA), to remove biological noise. Model parameters were estimated for Chlorella sp., and the model validated against additional data under both pulsed and continuous light. The average prediction error for OD750 (measure of biomass) was 8% under pulsed light and 15% under continuous light. For OD680/OD750 (measure of Chlorophyll cell−1) it was 8% under pulsed and continuous light, demonstrating the model’s ability to represent highly variable conditions with good accuracy.

Photosynthetic microalgae microbial fuel cells for bioelectricity generation and microalgae lipid recovery using Gd-Co@N-CSs/NF as cathode

Photosynthetic microalgae microbial fuel cells (PMMFCs) have an enormous potential for wastewater treatment and bioenergy recovery. However, to overcome low power generation problem, it is crucial to understand how the operational parameters influence the pathways and mechanisms of PMMFCs performance. In this study, microalgae (Chlorella vulgaris, Chlorella sp., Tetradesmus obliquus and Microcystis aeruginosa), light intensity (1400, 2100 and 3200 lx) and light/dark cycle (12/12, 18/6 and 24/0) were screened to promote the bioenergy recovery of PMMFCs. The highest power generation and electrochemical activity were obtained for Chlorella vulgaris under 3200 lx and cycle 18/6, with the maximum power density of 2.0 W m−3, and the lowest charge transfer resistance of 26.60 Ω and Tafel slope of 44.74 mV dec−1. Correlation analysis showed a significant negative correlation between NH4+-N concentration in the cathode chamber and output voltage. Structural equation model further elucidated that NH4+-N indirectly regulated the output voltage via the negative association with dissolved oxygen. In addition, the by-product lipid reached 145 mg g−1 dry mass. Furthermore, the specific gravity, iodine value, and cetane number of the fatty acids met the production standards for biodiesel. The electroactive bacteria Propionibacteriaceae (24.45%) were the dominant genera. This study provided suitable microalgae species and crucial operating conditions for bioenergy recovery from electrochemical systems with high catalytic activity.

Culture of photosynthetic microalgae consortium in artificial produced water supplemented with liquid digestate in closed column photobioreactors and open-pond raceway

Large amounts of produced water are extracted by the Oil and Gas energy sector since the industrial revolution. This available water, often salty, can be used to dilute liquid digestate from the anaerobic digestion process, a promising source of nutrients for microalgae cultivation. The study investigates the growth of halotolerant microalgae and their associated bacteria in column photobioreactors (PBRs) and open raceway pond (RWP), to treat industrial wastewaters while producing biomass for energy valorisation. Microalgae were cultured in mixtures of saline artificial produced water (7–44 %v/v), liquid digestate (5 %v/v using PBRs, 29–63 %v/v using RWP) and seawater. Nannochloropsis oceanica and Tetraselmis suecica strains were firstly cultivated in 70 L PBRs in indoor conditions for 3 months and later in 1.1 m3 RWP operated in outdoor conditions for 5 months in spring-summer period. In PBRs, average productivity was 9.0 ± 4.2 gVSS·m−2·d−1 (102–153 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 61.8, 31.6 and 97.2 %, respectively. In RWP, strong changes in the microalgae populations were observed. Productivity was 6.7 ± 5.2 gVSS·m−2·d−1 (30 ± 23 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 48.4, 44.4 and 88.1 %, respectively. In parallel with the production of microalgae, a nitrifying microbial population grew in the RWP despite the high salinity (70 g L−1). Over these periods of several months, microalgae production was maintained using a culture medium containing high salt concentration, metals and harmful aromatic compounds.

Space-Efficient 3D Microalgae Farming with Optimized Resource Utilization for Regenerative Food.

Photosynthetic microalgae produce valuable metabolites and are a source of sustainable food that supports life without compromising arable land. However, the light self-shading, excessive water supply, and insufficient space utilization in microalgae farming have limited its potential in the inland areas most in need of regenerative food solutions. Herein, this work develops a 3D polysaccharide-based hydrogel scaffold for vertically farming microalgae without needing liquid media. This liquid-free strategy is compatible with diverse microalgal species and enables the design of living microalgal frameworks with customizable architectures that enhance light and water utilization. This approach significantly increases microalgae yield per unit water consumption, with an 8.8-fold increase compared to traditional methods. Furthermore, the dehydrated hydrogels demonstrate a reduced size and weight (≈70% reduction), but readily recover their vitality upon rehydration. Importantly, valuable natural products can be produced in this system including proteins, carbohydrates, lipids, and carotenoids. This study streamlines microalgae regenerative farming for low-carbon biomanufacturing by minimizing light self-shading, relieving water supply, and reducing physical footprints, and democratizing access to efficient aquatic food production.

MYB Transcriptional Factors Affects Upstream and Downstream MEP Pathway and Triterpenoid Biosynthesis in Chlamydomonas reinhardtii

Terpenoids are enormous and different types of naturally occurring metabolites playing an important role in industrial applications. Cost-effective and sustainable production of terpenoids at commercial scale is the big challenge because of its low abundance from their natural sources. Metabolic and genetic engineering in microorganisms provide the ideal platform for heterologous overexpression protein systems. The photosynthetic green alga Chlamydomonas reinhardtii is considered as a model host for the production of economic and sustainable terpenoids, but the regulation mechanism of their metabolisms is still unclear. In this study, we have investigated the genetic and metabolic synthetic engineering strategy of MYB transcriptional factors (MYB TFs) in terpenoids’ synthesis from C. reinhardtii for the first time. We heterologous overexpressed MYB TFs, specifically SmMYB36 from Salvia miltiorrhiza in C. reinhardtii. MYB upregulated the key genes involved in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. Expression of the SQS gene, which is involved in the downstream triterpenoid synthesis pathway, highly accumulated in MYB-overexpression lines of C. reinhardtii. The contents of squalene increased about 90.20 μg/g in MYB-overexpressed lines. Our results propose the rerouting of the carbon flux toward the biosynthesis of triterpenoids upon overexpression of MYB TFs in C. reinhardtii. Our study suggests imperative novel understandings into the regulation mechanisms of C. reinhardtii triterpenoid metabolism through MYB TFs in photosynthetic green microalgae C. reinhardtii. The role of MYB TFs is investigated for the first time in C. reinhardtii, and provides a prodigious potential for recognizing important transcriptional regulators of the MEP pathway as goals for prospective metabolic and genetic manipulation investigation for increased production of triterpenoids.

Food waste upcycling via microalgal adaptive evolution for lipids and fatty acids enhancement towards circular bioeconomy

Disposal of food waste (FW) has become a significant problem that exacerbates the economy, environment and climate due to its rich nutrient content, thereby implying the necessity to upcycle FW by biotechnology means in a sustainable manner. Employing photosynthetic microalgae to FW upcycling hold great potential to simultaneously remediate the FW and to biosynthesize novel commodity metabolites. However, effective nutrient utilization of FW and metabolite overproduction by native algae is inadequate, and thus further development of strain and strategy is warranted to achieve a circular bioeconomy. Here, the marine Nannochloropsis oceanica was improved by adaptive laboratory evolution (ALE) under low salt conditions for enhanced lipid and uncompromised growth features. Then, FW hydrolysate (FWH) was used as the carbon source to facilitate the mixotrophic cultivation of N. oceanica. Results showed that the biomass of scrutinized evolved cells (ALE70) resulted in enhanced biomass production of 830 mg/l using FWH. Interestingly, ALE70 strains accumulate lipids up to 49 % of total cell dry weight, which was 1.5-fold higher than the WT cells cultivated in FWH. Importantly, FAME analysis by GC–MS showed that FWH provision to the ALE70 strains resulted in notable fatty acid alteration, enriched explicitly with unsaturated fatty acid and EPA content was hiked by 32 % of FAME. Altogether, these findings demonstrated a potential duplex strategy by employing the evolved strains to upcycle the food waste for valuable metabolite biosynthesis effectively and also offer promising insights into algal-associated food waste valorization towards circular bioeconomy.