Isolation of thermo-tolerant and high lipid content green microalgae: oil accumulation is predominantly controlled by photosystem efficiency during stress treatments in Desmodesmus

De novo transcriptome and lipidome analysis of Desmodesmus abundans under model flue gas reveals adaptive changes after ten years of acclimation to high CO2

Microalgae's ability to mitigate flue gas is an attractive technology that can valorize gas components through biomass conversion. However, tolerance and growth must be ideal; therefore, acclimation strategies are suggested. Here, we compared the transcriptome and lipidome of Desmodesmus abundans strains acclimated to high CO2 (HCA) and low CO2 (LCA) under continuous supply of model flue gas (MFG) and incomplete culture medium (BG11-N-S). Initial growth and nitrogen consumption from MFG were superior in strain HCA, reaching maximum productivity a day before strain LCA. However, similar productivities were attained at the end of the run, probably because maximum photobioreactor capacity was reached. RNA-seq analysis during exponential growth resulted in 16,435 up-regulated and 4,219 down-regulated contigs in strain HCA compared to LCA. Most differentially expressed genes (DEGs) were related to nucleotides, amino acids, C fixation, central carbon metabolism, and proton pumps. In all pathways, a higher number of up-regulated contigs with a greater magnitude of change were observed in strain HCA. Also, cellular component GO terms of chloroplast and photosystems, N transporters, and secondary metabolic pathways of interest, such as starch and triacylglycerols (TG), exhibited this pattern. RT-qPCR confirmed N transporters expression. Lipidome analysis showed increased glycerophospholipids in strain HCA, while LCA exhibited glycerolipids. Cell structure and biomass composition also revealed strains differences. HCA possessed a thicker cell wall and presented a higher content of pigments, while LCA accumulated starch and lipids, validating transcriptome and lipidome data. Overall, results showed significant differences between strains, where characteristic features of adaptation and tolerance to high CO2 might be related to the capacity to maintain a higher flux of internal C, regulate intracellular acidification, active N transporters, and synthesis of essential macromolecules for photosynthetic growth.

Chemical composition and species identification of microalgal biomass grown at pilot-scale with municipal wastewater and CO2 from flue gases

The production potential of a locally isolated Chlorella vulgaris strain and a local green-algae consortium, used in municipal wastewater treatment combined with CO₂ sequestration from flue gases, was evaluated for the first time by comparing the elemental and biochemical composition and heating value of the biomass produced. The microalgae were grown in outdoor pilot-scale ponds under subarctic summer conditions. The impact of cultivation in a greenhouse climate was also tested for the green-algae consortium; additionally, the variation in species composition over time in the three ponds was investigated. Our results showed that the biomass produced in the consortium/outdoor pond had the greatest potential for bioenergy production because both its carbohydrates and lipids contents were significantly higher than the biomasses from the consortium/greenhouse and C. vulgaris/outdoor ponds. Although greenhouse conditions significantly increased the consortium biomass's monounsaturated fatty acid content, which is ideal for biodiesel production, an undesirable increase in ash and chemical elements, as well as a reduction in heating value, were also observed. Thus, the placement of the pond inside a greenhouse did not improve the production potential of the green-algae consortium biomass in the current study infrastructure and climate conditions.

Mechanisms protect airborne green microalgae during long distance dispersal

Viable microalgae occur in the air. Whether they can survive the stresses such as UV, desiccation and freezing temperatures at high altitudes during long distance dispersal is rarely studied. If yes, what mechanisms confer the tolerance? Four freshwater airborne green microalgae were isolated from Dongsha Atoll in the South China Sea, classified as Scenedesmus sp. DSA1, Coelastrella sp. DSA2, Coelastrella sp. DSA3 and Desmodesmus sp. DSA6 based on their morphologies and ITS sequences. Their survival rates under UV stress were tightly correlated with their cell wall thickness. All the four airborne green microalgae survived the air-dry stress on benchtop followed by − 20 °C freeze–desiccation stress for 4 weeks, but not the two waterborne green microalgae Desmodesmus sp. F5 and Neodesmus sp. UTEX 2219-4 used as controls. Three of the four airborne microalgae survived the lyophilization treatment, excluding Desmodesmus sp. DSA6 and the two waterborne microalgae. The four airborne microalgae produced carotenoids under prolonged stress conditions, which might help detoxify the reactive oxygen species generated under environmental stresses and shield from the high-light stress in the air. Characterization of these airborne microalgae may help answer how the descendants of green algae survived on the land about 450 MYA.

Extremophile Microalgae: the potential for biotechnological application

Microalgae are photosynthetic microorganisms that use sunlight as an energy source, and convert water, carbon dioxide, and inorganic salts into algal biomass. The isolation and selection of microalgae, which allow one to obtain large amounts of biomass and valuable compounds, is a prerequisite for their successful industrial production. This work provides an overview of extremophile algae, where their ability to grow under harsh conditions and the corresponding accumulation of metabolites are addressed. Emphasis is placed on the high-value products of some prominent algae. Moreover, the most recent applications of these microorganisms and their potential exploitation in the context of astrobiology are taken into account.

Simultaneous wastewater treatment and lipid production by Scenedesmus sp. HXY2

Screening for highly efficient microalgae is an important technique for improving treatment efficiency. In this study, eight species of microalgae (five Scenedesmus and three Desmodesmus) were isolated from water and soil in the Hexi Corridor region, China, and identified by 18S rRNA gene sequence analysis. Scenedesmus sp. HXY2 grew well under high total organic carbon and ammonia conditions and had the highest nutrient removal efficiency (>95%). On day 12, the biomass of Scenedesmus sp. HXY2 was 7.2 × 10⁶ cells mL^-1. The lipid content and productivity of this species were 15.56% and 5.67 mg L^-1 day^-1, respectively. The proportion of unsaturated fatty acids (60.07%) indicated that the lipids of Scenedesmus sp. HXY2 were suitable for biodiesel production. Scenedesmus sp. HXY2 showed great potential for growth in wastewater with high ammonia and organic contents to simultaneously purify wastewater and produce lipids.

Effects of auxin derivatives on phenotypic plasticity and stress tolerance in five species of the green alga Desmodesmus (Chlorophyceae, Chlorophyta)

Green microalgae of the genus Desmodesmus are characterized by a high degree of phenotypic plasticity (i.e. colony morphology), allowing them to be truly cosmopolitan and withstand environmental fluctuations. This flexibility enables Desmodesmus to produce a phenotype–environment match across a range of environments broader compared to algae with more fixed phenotypes. Indoles and their derivatives are a well-known crucial class of heterocyclic compounds and are widespread in different species of plants, animals, and microorganisms. Indole-3-acetic acid (IAA) is the most common, naturally occurring plant hormone of the auxin class. IAA may behave as a signaling molecule in microorganisms, and the physiological cues of IAA may also trigger phenotypic plasticity responses in Desmodesmus. In this study, we demonstrated that the changes in colonial morphs (cells per coenobium) of five species of the green alga Desmodesmus were specific to IAA but not to the chemically more stable synthetic auxins, naphthalene-1-acetic acid and 2,4-dichlorophenoxyacetic acid. Moreover, inhibitors of auxin biosynthesis and polar auxin transport inhibited cell division. Notably, different algal species (even different intraspecific strains) exhibited phenotypic plasticity different to that correlated to IAA. Thus, the plasticity involving individual-level heterogeneity in morphological characteristics may be crucial for microalgae to adapt to changing or novel conditions, and IAA treatment potentially increases the tolerance of Desmodesmus algae to several stress conditions. In summary, our results provide circumstantial evidence for the hypothesized role of IAA as a diffusible signal in the communication between the microalga and microorganisms. This information is crucial for elucidation of the role of plant hormones in plankton ecology.

Draft Genome Sequence of the Biofuel-Relevant Microalga Desmodesmus armatus

A draft genome of 906 scaffolds of 115.8 Mb was assembled for Desmodesmus armatus, a diploid, lipid- and storage carbohydrate-accumulating microalga proven relevant for large-scale, outdoor cultivation, and serves as a model alga platform for improving photosynthetic efficiency and carbon assimilation for next-generation bioenergy production.

A draft genome of 906 scaffolds of 115.8 Mb was assembled for Desmodesmus armatus, a diploid, lipid- and storage carbohydrate-accumulating microalga proven relevant for large-scale, outdoor cultivation, and serves as a model alga platform for improving photosynthetic efficiency and carbon assimilation for next-generation bioenergy production.

Effects of nitrogen concentration on growth, biomass, and biochemical composition of Desmodesmus communis (E. Hegewald) E. Hegewald

Nitrogen, being one of the building blocks of biomacromolecules, is an important nutrient for microalgae growth. Nitrogen availability alters the growth and biochemical composition of microalgae. We investigated the effects of different nitrogen concentrations on specific growth rate (SGR), biomass productivity (BP), total protein and lipid content and amino acid and fatty acid composition of Desmodesmus communis. Nitrogen deficiency increased algal growth and changed the lipid amount and composition. The maximum growth and BP were detected in 75% N-medium. The highest total protein and lipid amount were detected in 50% N- and 75% N-media, respectively. Amino acid and fatty acid compositions of samples varied widely depending on the nutrient concentrations. The amount of unsaturated fatty acid (USFAs) was higher than saturated fatty acid (SFAs) and Linolenic acid percentage is higher than the limit of European standards in all media. The data reported here provide important contributions how nitrogen scarcity and abundance affect the growth and biochemical content of microalgae and this information can further be utilized in culture optimization in studies aimed at microalgae production for biofuels.

Disruption of thin- and thick-wall microalgae using high pressure gases: Effects of gas species, pressure and treatment duration on the extraction of proteins and carotenoids

Industrial scale microalgal cell disruption requires low cost, high efficiency and structural conservation of biomolecules for biorefinery. Many cultivated microalgae have thick walls and these walls are barriers for efficient cell disruption. Until recently, despite the high biodiversity of microalgae, little attention has been paid to thin-wall microalgal species in the natural environment for the production and recovery of valuable biomolecules. Instead of developing high power cell disruption devices, utilization of thin-wall species would be a better approach. The present paper describes a simple device that was assembled to evaluate the viability and effectiveness of biomolecule extraction from both thin- and thick-wall species as a proof of concept. This device was tested with high-pressure gases including N₂, CO₂ plus N₂, and air as the disruption force. The highest nitrogen pressure, 110 bar, was not able to disrupt the thick-wall microalgal cells. On the other hand, the thin-wall species was disrupted to different degrees using different pressures and treatment durations. In the same treatment duration, higher nitrogen pressure gave better cell disruption efficiency than the lower pressure. However, in the same pressure, longer treatment duration did not give better efficiency than the shorter duration. High pressure CO₂ treatments resulted in low soluble protein levels in the media. The best conditions to disrupt the thin-wall microalgal cells were 110 bar N₂ or air for 1 min among these tests. In these conditions, not only were the disruption efficiencies high, but also the biomolecules were well preserved.

Optimization of a simple, accurate and low cost method for starch quantification in green microalgae

BACKGROUND

Lipids and starch are important feedstocks for bioenergy production. Genetic studies on the biosyntheses of lipids and starch in green microalgae have drawn significant attention recently. In these studies, quantifications of lipids and starch are required to clarify the causal effects. While lipids are assayed with similar procedures worldwide, starch in green microalgae has been measured using various methods with deficiencies in accuracy or high cost.

RESULTS

A simple, accurate and low cost procedure for routine quantification of starch in green microalgae was developed. This procedure consists of quick-freezing of the cells, solvent extraction of the pigments, 134 °C autoclaving and glucoamylase double digestions of starch, followed by a glucose assay using the dinitrosalicylic acid reagent. This procedure was optimized to quantify starch in small volumes of green microalgal culture. The accuracy of starch quantification using this procedure was 102.3 ± 2.5% (mean ± SD, n = 6), as indicated by using cornstarch as internal controls. The working protocol is available at http://dx.doi.org/10.17504/protocols.io.2mhgc36 .

CONCLUSIONS

This quantification approach overcomes the current problems in the starch quantification of green microalgae such as inaccuracy and high cost. This approach would provide an opportunity to compare the effects of genetic, physiological or cultivation manipulations on the productivity of starch in green microalgae elucidated in different labs, which is essential in the enhancement of lipid productivity studies in microalgae.

Wastewater-leachate treatment by microalgae: Biomass, carbohydrate and lipid production

Increases in wastewater discharges and the generation of municipal solid wastes have resulted in deleterious effects on the environment, causing eutrophication and pollution of water bodies. It is therefore necessary to investigate sustainable bioremediation alternatives. Wastewater treatment using consortia of microalgae-bacteria is an attractive alternative because it allows the removal and recycling of nutrients, with the additional advantage of biomass production and its subsequent conversion into valuable by-products. The present study aims to integrate wastewater and landfill leachate treatment with the production of microalgal biomass, considering not only its valorization in terms of lipid and carbohydrate content but also the effect of nutrient limitation on biomass formation. The effect of treating a mixture of raw wastewater with different leachate ratios (0%, 7%, 10% and 15%) was investigated using a microalgae-bacteria consortium. Two microalgae (Desmodesmus spp. and Scenedesmus obliquus) were used. Nutrient removal, biomass concentration, carbohydrate, lipid and Fatty Acid Methyl Ester (FAMEs) content and morphological changes were evaluated. Removals of 82% of NH₄⁺ and 43% of orthophosphate from a wastewater-leachate mixture (containing 167 mg/L NH₄⁺ and 23 mg/L PO₄^3-) were achieved. The highest final yield was obtained using Desmodesmus spp. (1.95 ± 0.3 g/L). The microalgae were observed to accumulate high lipid (20%) and carbohydrate (41%) contents under nutrient limiting conditions. The concentration of Polyunsaturated Fatty Acids (PUFAs) also increased. Morphological changes including the disintegration of coenobia were observed. By using a mixture of wastewater-leachate it is possible to remove nutrients, since microalgae tolerate high ammonia concentrations, and simultaneously increase the algal biomass concentration containing precursors to allow biofuel production.

Caracterización <i>in silico</i> y análisis de la expresión de la subunidad alfa de la acetil-coenzima a carboxilasa heteromérica de dos microalgas

Las microalgas son microorganismos fotosintéticos con gran potencial para abastecer las demandas energéticas mundiales. Sin embargo, los limitados conocimientos que se tienen de estos organismos, en particular a nivel molecular de los procesos metabólicos, han limitado su uso con estos propósitos. En esta investigación se ha realizado el análisis in silico de la subunidad alfa de la acetil-Coenzima A carboxilasa heteromérica (αACCasa), una enzima clave en la biosíntesis de lípidos de las microalgas Chlorella sp. y Scenedesmus sp. Asimismo, se ha medido la expresión de este gen en ambas especies cultivadas en medios deficientes de nitrógeno. Los resultados indican que la αACCasa muestra conservación estructural y funcional en ambas especies de microalgas y su mayor similitud genética con otras especies de microalgas. Asimismo, se ha mostrado que el nivel de expresión del gen se incrementa significativamente cuando las microalgas son cultivadas en ausencia de nitrógeno, lo cual se relaciona a su vez con una mayor acumulación de lípidos microalgales. En conclusión, el análisis in silico de la αACCasa de Chlorella sp. y Scenedesmus sp. presentan características estructurales, funcionales y evolutivas muy similares con otras especies de microalgas y plantas. Asimismo, el estudio revela que en ambas especies el gen se sobreexpresa cuando las microalgas son sometidas a estrés por deficiencia de nitrógeno, el cual se relaciona significativamente con la acumulación de lípidos totales en estas células.

A new application of Trichoderma asperellum as an anopheline larvicide for eco friendly management in medical science

Microfungal applications are increasing daily in the medical science. Several species of Trichoderma are widely used in agricultural fields as biological control and plant growth promoting agents. The application of Trichoderma asperellum as an entomopathogenic fungus against the Anopheles mosquito, a vector of malaria, is a novel control approach. Controlling malaria with eco-friendly management practices is an urgent need. We isolated three T. asperellum from different natural sources using serial dilution and mosquito baiting techniques. The fungi were identified on the basis of phenotypical and molecular characteristics. The fungi were grown in different natural media to examine spore production ability and the fungal spore suspensions were applied to the anopheline larvae to determine their larvicidal activity in vitro. We investigated the efficacy of crude ME (methanolic extract) and different methanolic fractions (MFs) of the fungal extracts against anopheline larvae. Methanolic Fraction 8 (MF8) exhibited the strongest larvicidal activity. A GC-MS analysis of MF8 and a Chemolibrary search were performed to identify the active agents in the fungal extracts. Among the three isolates of T. asperellum, the TaspSKGN2 isolate showed the lowest LD50 (2.68 × 107 conidia/mL) and LT50 values (12.33 h). The crude ME exhibited LD50 values of 0.073 mg/mL and LT50 values of 11.33 h. MF8 showed LD50 values of 0.059 mg/mL and LT50 values of 8.57 h. In GC-MS study of MF8, 49 compounds were found. Among these, seven compounds (2,3-di hydro thiopene, p-cymene, alpha-pinene, hexadecanoic acid, 8-methyl quinoline, (Z,Z)-9,12-octa decadienoic acid, methyl ester, 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-Pyran-4-one-) with high abundance were found to have insecticidal efficacy by a literature survey. We detected a reduction in the phenoloxidase content inside the cuticle and hemolymph of the anopheline larvae after a few hours of interaction with ME (0.073 mg/mL). Thus Trichoderma asperellum has new applications for the control of Anopheles spp. malaria vectors.

Achieving efficient nitrogen removal and nutrient recovery from wastewater in a combining simultaneous partial nitrification, anammox and denitrification (SNAD) process with a photobioreactor (PBR) for biomass production and generated dissolved oxygen (DO) recycling

This study presents a new way to achieve energy neutral wastewater treatment based on a combined nitrification, anammox, and denitrification (SNAD) process and photobioreactor (PBR) configuration with external recycling instead of aeration, and without an additional carbon source, using fixed-film-activated sludge technology (IFAS). The SNAD-PBR process achieved total nitrogen (TN) and phosphorus removal efficiencies of 90 and 100%, respectively. In addition, dissolved oxygen (DO) was controlled in the range 0.4-1.2 mg/L by the introduction of an external recycling system. The presence of microalgae to serve as a carbon source in the SNAD reactor enabled the denitrifiers to survive. When the reflux ratio was 1:3, the lower COD/N protected the activity of the anammox bacteria, not suppressed by the heterotrophic denitrifiers. Microbial community analysis by Illumina MiSeq sequencing revealed that the new environment was more suitable for Candidatus Brocadia when a reflux system was introduced.

Photosynthetic physiological performance and proteomic profiling of the oleaginous algae Scenedesmus acuminatus reveal the mechanism of lipid accumulation under low and high nitrogen supplies

In this study, we presented cellular morphological changes, time-resolved biochemical composition, photosynthetic performance and proteomic profiling to capture the photosynthetic physiological response of Scenedesmus acuminatus under low nitrogen (3.6 mM NaNO₃, N^-) and high nitrogen supplies (18.0 mM NaNO₃, N⁺). S. acuminatus cells showed extensive lipid accumulation (53.7% of dry weight) and were enriched in long-chain fatty acids (C16 & C18) under low nitrogen supply. The activity of PSII and photosynthetic rate decreases, whereas non-photochemical quenching and dark respiration rates were increased in the N^- group. In addition, the results indicated a redistribution of light excitation energy between PSII and PSI in S. acuminatus exists before lipid accumulation. The iTRAQ results showed that, under high nitrogen supply, protein abundance of the chlorophyll biosynthesis, the Calvin cycle and ribosomal proteins decreased in S. acuminatus. In contrast, proteins associated with the photosynthetic machinery, except for F-type ATPase, were increased in the N⁺ group (N⁺, 3 vs. 9 days and 3 days, N⁺ vs. N^-). Under low nitrogen supply, proteins involved in central carbon metabolism, fatty acid synthesis and branched-chain amino acid metabolism were increased, whereas the abundance of proteins of the photosynthetic machinery had decreased, with exception of PSI (N^-, 3 vs. 9 days and 9 days, N⁺ vs. N^-). Collectively, the current study has provided a basis for the metabolic engineering of S. acuminatus for biofuel production.

Indole-3-acetic-acid-induced phenotypic plasticity in Desmodesmus algae

Phenotypic plasticity is the ability of a single genotype of an organism to exhibit variable phenotypes in response to fluctuating environments. It plays a crucial role in their evolutionary success. In natural environments, the importance of interactions between microalgae and other microorganisms is generally well appreciated, but the effects of these interactions on algal phenotypic plasticity has not been investigated. In this study, it revealed that indole-3-acetic acid (IAA), the most common naturally occurring plant hormone, can exert stimulatory at low concentrations and inhibitory effects at high concentrations on the growth of the green alga Desmodesmus. The morphological characteristics of Desmodesmus changed drastically under exposure to IAA compared with the algae in the control environment. The proportion of Desmodesmus unicells in monocultures increased with the IAA concentration, and these unicells exhibited less possibility of sedimentation than large cells. Furthermore, we discovered that lipid droplets accumulated in algal cells grown at a high IAA concentration. Results also demonstrated that the presence of algal competitor further stimulated inducible morphological changes in Desmodesmus populations. The relative abundance of competitors influenced the proportion of induced morphological changes. The results indicate that phenotypic plasticity in microalgae can be a response to fluctuating environments, in which algae optimize the cost–benefit ratio.

Extremophiles for microbial-electrochemistry applications: A critical review

Extremophiles, notably archaea and bacteria, offer a good platform for treating industrial waste streams that were previously perceived as hostile to the model organisms in microbial electrochemical systems (MESs). Here we present a critical overview of the fundamental and applied biology aspects of halophiles and thermophiles in MESs. The current study suggests that extremophiles enable the MES operations under a seemingly harsh conditions imposed by the physical (pressure, radiation, and temperature) and geochemical extremes (oxygen levels, pH, and salinity). We highlight a need to identify the underpinning mechanisms that define the exceptional electrocatalytic performance of extremophiles in MESs.

Fatty acids from high rate algal pond's microalgal biomass and osmotic stress effects

The extraction of oil from a wild microalgae biomass collected from a domestic wastewater treatment facility's high rate algal pond (HRAP) was investigated. An experiment plan was used to determine the most efficient extraction method, the optimal temperature, time and solvent system based on total lipids yield. Microwave-assisted extraction was the most efficient method whether in n-hexane or in a mixture of chloroform/methanol compared to Soxhlet, homogenization, and ultrasounds assisted extractions. This same wild biomass was cultivated in a photobioreactor (PBR) and the effect of osmotic stress was studied. The lipids extraction yield after 3days of stress increased by more than four folds without any significant loss of biomass, however, the quality of extracted total lipids in terms of saturated, monounsaturated and polyunsaturated fatty acids was not affected by salinity change in the culture medium.

The effect of growth phase on the surface properties of three oleaginous microalgae (Botryococcus sp. FACGB-762, Chlorella sp. XJ-445 and Desmodesmus bijugatus XJ-231)

The effects of growth phase on the lipid content and surface properties of oleaginous microalgae Botryococcus sp. FACGB-762, Chlorella sp. XJ-445 and Desmodesmus bijugatus XJ-231 were investigated in this study. The results showed that throughout the growth phases, the lipid content of microalgae increased. The surface properties like particle size, the degree of hydrophobicity, and the total concentration of functional groups increased while net surface zeta potential decreased. The results suggested that the growth stage had significant influence not only on the lipid content but also on the surface characteristics. Moreover, the lipid content was significantly positively related to the concentration of hydroxyl functional groups in spite of algal strains or growth phases. These results provided a basis for further studies on the refinery process using oleaginous microalgae for biofuel production.

Microalgal hydrogen production: prospects of an essential technology for a clean and sustainable energy economy

Modern energy production is required to undergo a dramatic transformation. It will have to replace fossil fuel use by a sustainable and clean energy economy while meeting the growing world energy needs. This review analyzes the current energy sector, available energy sources, and energy conversion technologies. Solar energy is the only energy source with the potential to fully replace fossil fuels, and hydrogen is a crucial energy carrier for ensuring energy availability across the globe. The importance of photosynthetic hydrogen production for a solar-powered hydrogen economy is highlighted and the development and potential of this technology are discussed. Much successful research for improved photosynthetic hydrogen production under laboratory conditions has been reported, and attempts are underway to develop upscale systems. We suggest that a process of integrating these achievements into one system to strive for efficient sustainable energy conversion is already justified. Pursuing this goal may lead to a mature technology for industrial deployment.

Overexpression of the 16-kDa α-amylase/trypsin inhibitor RAG2 improves grain yield and quality of rice

Increasing grain yield and improving grain quality are two important goals for rice breeding. A better understanding of the factors that contribute to the overall grain quantity and nutritional quality of rice will lay the foundation for developing new breeding strategies. RAG2 is a member of 14-to-16-kDa α-amylase/trypsin inhibitors in rice, which belong to the albumin of seed storage proteins. We found that RAG2 was specifically expressed in ripening seed and its transcription peak was between 14 and 21 days after flowering. Grain size and 1000-grain weight were obviously increased in RAG2-overexpressed lines compared with wild type, and grain size was reduced in RAG2-suppressed lines. In addition, the major storage substances of the seeds differed significantly in RAG2-overexpressed and RAG2-suppressed lines compared to wild type. The protein content and amount of total lipids were increased and decreased, respectively, in the seeds of RAG2-overexpressed and RAG2-suppressed lines. Overexpression of RAG2 significantly increased grain size and improved grain quality and yield simultaneously. These results imply that RAG2 might play an important role in regulating grain weight and seed quality of rice. The functional characterization of rice RAG2 facilitates a further understanding of the mechanisms involved in grain size and seed quality and may be helpful in improving grain yield and quantity in cereal crops.

Enhanced lipid production in thermo-tolerant mutants of Chlorella pyrenoidosa NCIM 2738

The present study aimed to develop thermo-tolerant mutants of Chlorella pyrenoidosa NCIM 2738 for high lipids production. For this, ethyl methane sulfonate was used, which generated two effective thermo-tolerant mutants, M18 and M24 of Chlorella pyrenoidosa NCIM 2738, capable of surviving at temperature up to 47°C and showing improved lipid and biomass yields. They showed 59.62% and 50.75% increase, respectively in lipid content compared to wild type at 30°C, which could not grow at temperature above 35°C. The novelty of this study lied in incorporation of PAM Flurometry with mutagenesis to generate thermo-tolerant mutants of C. pyrenoidosa and investigating the reasons for increased yields of mutants at cellular and photosynthetic levels with the aim to use them for commercial biodiesel production.

Cultivation of two thermotolerant microalgae under tropical conditions: Influences of carbon sources and light duration on biomass and lutein productivity in four seasons

Biomass and lutein productivities of two thermotolerant microalgae were assessed in tropical outdoor conditions in all four seasons. Generally, addition of bicarbonate at 0.2g/L every two days or 2% CO2 did not enhance the productivities compared to the controls, and the productivities in the spring were higher than in the fall. Durations of effective irradiance positively correlated to the productivity of Coelastrella sp. F50 well, but not for Desmodesmus sp. F2. The ineffective light intensity was below 5000 lux (about 106μmol/m(2)s). The productivities produced in the 17cm diameter bottles were 1.5- to 1.9-fold higher than that in the 27cm ones. Lutein content, about 0.5% in biomass on average, did not change significantly grown in different carbon sources or seasons. The annual productivities of the microalgal biomass and lutein in one hectare were estimated to be 33tons and 180kg, respectively, using the non-optimized photobioreactor cultivation.

Effective cultivation of microalgae for biofuel production: a pilot-scale evaluation of a novel oleaginous microalga Graesiella sp. WBG-1

BACKGROUND

Commercial production of microalgal biodiesel is not yet economically viable, largely because of low storage lipid yield in microalgae mass cultivation. Selection of lipid-rich microalgae, thus, becomes one of the key research topics for microalgal biodiesel production. However, the laboratory screening protocols alone cannot predict the ability of the strains to dominate and perform in outdoor ponds. Comprehensive assessment of microalgae species should be performed not only under the laboratory conditions, but also in the fields.

RESULTS

Laboratory investigations using a bubbled column photobioreactor indicated the microalga Graesiella sp. WBG-1 to be the most productive species among the 63 Chlorophyta strains. In a 10 L reactor, mimicking the industrial circular pond, Graesiella sp. WBG-1 produced 12.03 g biomass m(-2) day(-1) and 5.44 g lipids (45.23 % DW) m(-2) day(-1) under 15 mol m(-2) day(-1) artificial light irradiations. The lipid content decreased to ~34 % DW when the microalga was cultured in 30 L tank PBR under natural solar irradiations, but the decline of lipid content with scaling up was the minimum among the tested strains. Based on these results, the microalga was further tested for its lipid production and culture competitiveness using a pilot-scale raceway pond (200 m(2) illuminated area, culture volume 40,000 L). Consequently, Graesiella sp. WBG-1 maintained a high lipid content (33.4 % DW), of which ~90 % was storage TAGs. Results from the outdoor experiments indicated the nice adaptability of the Graesiella sp. WBG-1 to strong and fluctuating natural solar irradiance and temperature, and also demonstrated several other features, such as large cell size (easy for harvest and resistant to swallow by protozoa) and tolerance to high culture pH (helpful to CO2 fixation).

CONCLUSIONS

Graesiella sp. WBG-1 was a promising strain capable of accumulating large amount of storage lipid under nature solar irradiance and temperature. The high lipid content of 33.4 % DW was achieved for the first time in pilot-scale raceway pond. The results also provide evidence for the feasibility of using low-cost raceway pond for autotrophic cultivation of microalgae for biodiesel production.

Mixed Wastewater Coupled with CO2 for Microalgae Culturing and Nutrient Removal

Biomass, nutrient removal capacity, lipid productivity and morphological changes of Chlorella sorokiniana and Desmodesmus communis were investigated in mixed wastewaters with different CO₂ concentrations. Under optimal condition, which was 1:3 ratio of swine wastewater to second treated municipal wastewater with 5% CO₂, the maximum biomass concentrations were 1.22 g L^-1 and 0.84 g L^-1 for C. sorokiniana and D. communis, respectively. Almost all of the ammonia and phosphorus were removed, the removal rates of total nitrogen were 88.05% for C. sorokiniana and 83.18% for D. communis. Lipid content reached 17.04% for C. sorokiniana and 20.37% for D. communis after 10 days culture. CO₂ aeration increased intracellular particle numbers of both microalgae and made D. communis tend to be solitary. The research suggested the aeration of CO₂ improve the tolerance of microalgae to high concentration of NH₄-N, and nutrient excess stress could induce lipid accumulation of microalgae.

Production of long chain omega-3 fatty acids and carotenoids in tropical areas by a new heat-tolerant microalga Tetraselmis sp. DS3

Demand for long chain ω-3 fatty acids from non-fish source for vegetarians has increased recently. Marine microalgae are the primary producers of EPA/DHA and promising alternatives for fish oil. Tropical areas have abundant sunlight throughout the year for microalgal cultivation but this practice can be hindered by high temperature. Discovery of heat-tolerant marine microalgae that can synthesize EPA/DHA will solve these problems. A new species of microalga was isolated from a high temperature lagoon and identified as Tetraselmis sp. DS3. These cells could grow at 40 °C, the highest temperature for marine microalgal growth ever reported. Its ω-3 fatty acids and EPA accounted for 33 and 10% of total lipids, respectively, grown in nitrogen-depleted conditions. These cells also accumulated more than 5% β-carotene and 0.48% lutein in biomass. This new microalga can be cultivated for long chain ω-3 fatty acids and lutein production in the tropical areas.

Similarity and diversity of the Desmodesmus spp. microalgae isolated from associations with White Sea invertebrates

Similarity and diversity of the phenotype and nucleotide sequences of certain genome loci among the single-celled microalgae isolated from White Sea benthic invertebrates were studied to extend the knowledge of oxygenic photoautotrophs forming microbial communities associated with animals. We compared four Desmodesmus isolates (1Hp86E-2, 1Pm66B, 3Dp86E-1, 2Cl66E) from the sponge Halichondria panicea, trochophore larvae of the polychaete Phyllodoce maculata, and the hydroids Dynamena pumila and Coryne lovenii, respectively. The microalgae appeared to be very similar featuring the phenotypic and genetic traits characteristics of unicellular representatives of the genus Desmodesmus. At the same time, isolates from different animal species displayed certain differences in (i) the epistructure morphology; (ii) type and number of the inclusions such as interthylakoid starch grains and cytoplasmic oil bodies and (iii) fatty acid composition; in Desmodesmus sp. 1Hp86E-2, these differences were most pronounced. Phylogenetic analysis based on ITS1-5.8S rRNA-ITS2 and rbcL sequences showed that all isolates studied differ from known classified representatives of Desmodesmus combining a deletion in the conservative 5.8S rRNA gene and long AC-microsatellite repeats in the ITS1 whereas 1Hp86E-2 represented a distinct branch within this group.

Coordinated response of photosynthesis, carbon assimilation, and triacylglycerol accumulation to nitrogen starvation in the marine microalgae Isochrysis zhangjiangensis (Haptophyta)

The photosynthetic performance, carbon assimilation, and triacylglycerol accumulation of Isochrysis zhangjiangensis under nitrogen-deplete conditions were studied to understand the intrinsic correlations between them. The nitrogen-deplete period was divided into two stages based on the photosynthetic parameters. During the first stage, carbon assimilation was not reduced compared with that under favorable conditions. The marked increase in triacylglycerols and the variation in the fatty acid profile suggested that triacylglycerols were mainly derived from de novo synthesized acyl groups. In the second stage, the triacylglycerol content continued increasing while the carbohydrate content decreased from 44.0% to 26.3%. These results indicated that the intracellular conversion of carbohydrates to triacylglycerols occurred. Thus, we propose that sustainable carbon assimilation and incremental triacylglycerol production can be achieved by supplying appropriate amounts of nitrogen in medium to protect the photosynthetic process from severe damage using the photosynthetic parameters as indicators.

Selection of microalgae for biodiesel production in a scalable outdoor photobioreactor in north China

The aim of this study was to identify the most promising species as biodiesel feedstock for large-scale cultivation in north China. Eight species of microalgae, selected on the basis of indoor screening, were tested for lipid productivity and the suitability of their fatty acid profiles for biodiesel production under outdoor conditions. Among them, three species Desmodesmus sp. NMX451, Desmodesmus sp. T28-1 and Scenedesmusobtusus XJ-15 were selected for further characterization due to their possessing higher lipid productivities and favorable biodiesel properties. The best strain was S. obtusus XJ-15, with highest biomass productivity of 20.2gm(-2)d(-1) and highest lipid content of 31.7% in a culture of 140L. S. obtusus XJ-15 was further identified as the best candidate for liquid biofuel production, characterized by average areal growth rate of 23.8gm(-2)d(-1) and stable lipid content of above 31.0% under a scale of 1400L over a season.

Identification of carbohydrates as the major carbon sink of the marine microalga Isochrysis zhangjiangensis (Haptophyta) and optimization of its productivity by nitrogen manipulation

Microalgae represent a potential feedstock for biofuel production. During cultivation under nitrogen-depleted conditions, carbohydrates, rather than neutral lipids, were the major carbon sink of the marine microalga Isochrysis zhangjiangensis (Haptophyta). Carbohydrates reached maximum levels of 21.2 pg cell(-1) on day 5, which was an increase of more than 7-fold from day 1, while neutral lipids simultaneously increased 1.9-fold from 4.0 to 7.6 pg cell(-1) during the ten-day nitrogen-depleted cultivation. The carbohydrate productivity of I. zhangjiangensis was improved by optimization of the nitrate supply mode. The maximum carbohydrate concentration was 0.95 g L(-1) under batch cultivation, with an initial nitrogen concentration of 31.0 mg L(-1), which was 2.4-fold greater than that achieved under nitrogen-depleted conditions. High performance liquid chromatography (HPLC) analysis showed that the accumulated carbohydrate in I. zhangjiangensis was composed of glucose. These results show that I. zhangjiangensis represents an ideal carbohydrate-enriched bioresource for biofuel production.

Exploring the high lipid production potential of a thermotolerant microalga using statistical optimization and semi-continuous cultivation

A recently isolated thermotolerant microalga Desmodesmus sp. F2 has the traits of becoming potential biodiesel feedstock, such as high growth rate, high lipid content, and quick precipitation. Its overall lipid productivity was 113 mg/L/d when grown under non-optimal conditions using batch cultivation. A two-step response surface methodology was adopted to optimize its cultivation conditions. The overall lipid productivity was increased to 263 mg/L/d when the cells were grown under the optimized conditions of 6.6mM initial nitrogen level and 6 days nitrogen depletion treatment in 700 μmol/m(2)/s light intensity at 35°C using batch cultivation. Fed-batch and semi-continuous cultivations were employed to further increase its lipid productivity to 213 and 302 mg/L/d, respectively. The 302 mg/L/d is the highest overall lipid productivity of microalgae ever reported in the literature. This study provides the information required for the design and operation of photobioreactors for large scale outdoor cultivation of this species.

Isolation of novel microalgae from acid mine drainage and its potential application for biodiesel production

Microalgae were selected and isolated from acid mine drainage in order to find microalgae species which could be cultivated in low pH condition. In the present investigation, 30 microalgae were isolated from ten locations of acid mine drainage in South Korea. Four microalgae were selected based on their growth rate, morphology, and identified as strains of KGE1, KGE3, KGE4, and KGE7. The dry biomass of microalgae species ranged between 1 and 2 g L(-1) after 21 days of cultivation. The growth kinetics of microalgae was well described by logistic growth model. Among these, KGE7 has the highest biomass production (2.05 ± 0.35 g L(-1)), lipid productivity (0.82 ± 0.14 g L(-1)), and C16-C18 fatty acid contents (97.6 %). These results suggest that Scenedesmus sp. KGE 7 can be utilized for biodiesel production based on its high biomass and lipid productivity.

Enhanced lipid production in Chlorella pyrenoidosa by continuous culture

Usually microalgae growth and lipid accumulation do not run in parallel throughout cultivation, which necessarily lowers overall lipid productivity. However, we show through batch and feed-batch studies of Chlorella pyrenoidosa XQ-20044 that by varying the nitrate concentration, conditions which produce fairly high lipid content could be achieved without sacrificing algal growth. Simultaneous microalgae growth and lipid production was achieved in continuous chemostat culture when the specific nitrate input rate was in the range of 0.78-4.56mmolg(-1)d(-1). Moreover, the maximum lipid productivity (144.93mgL(-1)d(-1)) in the continuous culture was significantly higher than in batch culture (96.28mgL(-1)d(-1)), thus indicating the feasibility and great advantage of one-step production of microalgal lipids.

NaCl as an effective inducer for lipid accumulation in freshwater microalgae Desmodesmus abundans

In order to evaluate the efficiency and potential of salt addition-based two-stage cultivation technology, on the basis of urea as nitrogen source, we compared four types of salts (NaCl, NaHCO3, NaS2O3 and NaAc) as inducers for lipid production in Desmodesmus abundans. The maximum biomass productivity (270.08mgL(-1)d(-1)) was obtained by using 0.25gL(-1) urea. The highest lipid productivity (67.08mgL(-1)d(-1)) and better biodiesel quality were realized by addition of 20gL(-1) NaCl, and the optimal time point for salt addition was determined at 1.79gL(-1) of biomass density. Further cost analysis demonstrated this cultivation process was relatively economical. Above results suggest that NaCl addition is an economical and applicable strategy for lipid enhancement and can be extended for microalgae-based biodiesel production.

Bioprospecting for acidophilic lipid-rich green microalgae isolated from abandoned mine site water bodies

With fossil fuel sources in limited supply, microalgae show tremendous promise as a carbon neutral source of biofuel. Current microalgae biofuel strategies typically rely on growing high-lipid producing laboratory strains of microalgae in open raceways or closed system photobioreactors. Unfortunately, these microalgae species are found to be sensitive to environmental stresses or competition by regional strains. Contamination by invasive species can diminish productivity of commercial algal processes. A potential improvement to current strategies is to identify high-lipid producing microalgae, which thrive in selected culture conditions that reduce the risk of contamination, such as low pH. Here we report the identification of a novel high-lipid producing microalgae which can tolerate low pH growth conditions. Lig 290 is a Scenedesmus spp. isolated from a low pH waterbody (pH = 4.5) in proximity to an abandoned lignite mine in Northern Ontario, Canada. Compared to a laboratory strain of Scendesmus dimorphus, Lig 290 demonstrated robust growth rates, a strong growth profile, and high lipid production. As a consequence, Lig 290 may have potential application as a robust microalgal species for use in biofuel production.

Achieving high lipid productivity of a thermotolerant microalga Desmodesmus sp. F2 by optimizing environmental factors and nutrient conditions

The optimal conditions for cultivating the thermotolerant lipid-rich microalga Desmodesmus sp. F2 to achieve maximal lipid productivity were determined in this study. The conditions were light intensity, 700μmol/m(2)s; temperature, 35°C; cultivation nitrogen source, nitrate; initial nitrogen level, 6.6mM nitrogen. Carbon dioxide (2.5%, 0.2 vvm) was pumped into the cultures continuously. In the pre-optimized conditions, the maximal lipid productivity of this microalga was 113mg/L/d, which was raised to 263mg/L/d in the optimized conditions. This level of lipid productivity of microalgae is the highest ever reported in the literature. Fatty acid composition of the lipid produced by Desmodesmus sp. F2 in the optimal conditions was determined, in which C16 and C18 species accounted for 95% of the fatty acids. Saturated, monounsaturated and polyunsaturated fatty acids accounted for 38.9%, 33.1% and 22.6%, respectively. Based on the analysis, this lipid quality makes it a good feedstock for biodiesel production.

Equilibrium and kinetics of phosphorous adsorption onto bone charcoal from aqueous solution

Pyrolysis of fresh sheep bone led to the formation of bone charcoal (BC). The structural characteristics of BC and surface area were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). N2 gas adsorption-desorption was analysed by Brunauer-Emmett-Teller isotherm model. The prepared BC was used as an effective sorbent for the removal of phosphate from aqueous solutions. The effect of major parameters, including initial phosphorous concentration, sorbent dosage, pH and temperature, was investigated in this study. Furthermore, adsorption isotherms and kinetics were evaluated. BC was an effective sorbent in phosphate removal from aqueous solution especially in phosphate concentration between 2 and 100 mg/L. The maximum amount of sorption capacity was 30.21 mg/g, which was obtained with 100 mg/L as the initial phosphate concentration and 0.2 g as the sorbent dosage. Best reported pH in this study is 4; in higher pH, adsorption rate decreased dramatically. By increasing the temperature from 20 to 40 degrees C sorption capacity increased; this phenomenon described that adsorption is endothermic. Equilibrium data were analysed by Langmuir, Freundlich and Temkin isotherms. Pseudo first- and second-order and Elovich models were used to determine the kinetics of adsorption in this study. Collected data highly fitted with Freundlich isotherms and pseudo second-order kinetics. Achieved results have shown well the potentiality for the BC to be utilized as a natural sorbent to remove phosphorous from water and wastewater.

Selection of elite microalgae for biodiesel production in tropical conditions using a standardized platform

Four thermotolerant microalgae were isolated from tropical Taiwan and classified as members of Desmodesmus based on morphological and molecular studies. A platform was established to evaluate their biodiesel production-related traits, including thermotolerance, lipid productivity, lipid oxidative stability and auto-sedimentation. The findings demonstrated thermotolerance of all four species was at the same level, as all could live at 45 °C for 24 h and 50 °C for 8 h with mortality rates below 5% of cells. The lipid productivity of Desmodesmus sp. F2 reached 113 mg/L/d. Its saturated and monounsaturated fatty acids accounted for 75% of the FAMEs, and it required only 3.1 h to achieve 85% sedimentation. Comparing these traits to those of the other three Desmodesmus and microalgae in the literature, Desmodesmus sp. F2 is one of the best candidates for biodiesel production in tropical and subtropical areas. This platform effectively assessed traits of microalgae related to biodiesel production.

Isolation of a novel microalgae strain Desmodesmus sp. and optimization of environmental factors for its biomass production

A novel strain of unicellular green algae was isolated from fresh water samples collected from Yesanpo National Geopark, Laishui County of Hebei Province, China. The morphological and genomic identification of this strain was carried out using 18s rRNA analysis. This novel strain was identified as Desmodesmus sp. named as EJ15-2. Environmental factors for biomass production of Desmodesmus sp. EJ15-2 grown under autotrophic condition (BG11 medium) was optimized using response surface methodology (RSM). A high correlation coefficient (R(2)=0.923, p ≤ 0.01) indicated the adaptability of the second-order equation matched well with the growth condition of this strain. The optimal conditions for a relatively high biomass production (up to 0.758 g/L) were at 30°C, 98 μmol/m(2)/s and 14:10 (L:D), respectively.

Highlights from the Indo-US workshop "Cyanobacteria: molecular networks to biofuels" held at Lonavala, India during December 16-20, 2012

An Indo-US workshop on "Cyanobacteria: molecular networks to biofuels" was held December 16-20, 2012 at Lagoona Resort, Lonavala, India. The workshop was jointly organized by two of the authors, PPW, a chemical engineer and LAS, a biologist, thereby ensuring a broad and cross-disciplinary participation. The main objective of the workshop was to bring researchers from academia and industry of the two countries together with common interests in cyanobacteria or microalgae and derived biofuels. An exchange of ideas resulted from a series of oral and poster presentations and, importantly, through one-on-one discussions during tea breaks and meals. Another key objective was to introduce young researchers of India to the exciting field of cyanobacterial physiology, modeling, and biofuels. PhD students and early stage researchers were especially encouraged to participate and about half of the 75 participants belonged to this category. The rest were comprised of senior researchers, including 13-15 invited speakers from each country. Overall, twenty-four institutes from 12 states of India were represented. The deliberations, which are being compiled in the present special issue, revolved mainly around molecular aspects of cyanobacterial biofuels including metabolic engineering, networks, genetic regulation, circadian rhythms, and stress responses. Representatives of some key funding agencies and industry provided a perspective and opportunities in the field and for bilateral collaboration. This article summarizes deliberations that took place at the meeting and provides a bird's eye view of the ongoing research in the field in the two countries.

A model for customising biomass composition in continuous microalgae production

A kinetic model is presented that describes functional biomass, starch and storage lipid (TAG) synthesis in the microalga Neochloris oleoabundans as a function of nitrogen and light supply rates to a nitrogen-limited turbidostat cultivation system. The model is based on the measured electron distribution in N. oleoabundans, which showed that starch is the primary storage component, whereas TAG was only produced after an excess of electrons was generated, when growth was limited by nitrogen supply. A fixed 8.6% of the excess electrons ended up in TAG, suggesting close metabolic interactions between nitrogen assimilation and TAG accumulation, such as a shared electron pool. The proposed model shows that by manipulating the cultivation conditions in a light or nitrogen limited turbidostat, algal biomass composition can be customised and the volumetric productivities and yields of the major biomass constituents can be changed on demand.

Salinity manipulation as an effective method for enhanced starch production in the marine microalga Tetraselmis subcordiformis

Microalgal starch is considered a promising feedstock for bioethanol production. The biomass and starch accumulation in the marine microalga Tetraselmis subcordiformis were characterized under different salinities in response to nitrogen repletion (+N) or depletion (-N) at high irradiance (HI) or low irradiance (LI). Under favorable nutritional conditions (HI+N), biomass accumulation was seldom affected under 20% normal salinity, though starch accumulation were somewhat reduced. Increased salinity impaired overall biomass and starch accumulation, though it led to a temporary starch accumulation at initial cultivation phase. Under nitrogen deprivation, decreased salinity strengthened biomass and starch accumulation regardless of irradiance. The highest starch content of 58.2% dry weight and starch productivity of 0.62 g L(-1) d(-1) were obtained under HI-N with 20% normal salinity. Decreased salinity combined with -N generated moderate stress to facilitate starch accumulation. Salinity manipulation can be effectively applied for enhanced starch production in marine microalgae.

Phototrophic cultivation of a thermo-tolerant Desmodesmus sp. for lutein production: effects of nitrate concentration, light intensity and fed-batch operation

Four indigenous thermo-tolerant Desmodesmus sp. strains were examined for their ability to produce lutein. Among them, Desmodesmus sp. F51 was the best strain for this purpose. The medium composition, nitrate concentration and light intensity were manipulated to improve the phototrophic growth and lutein production of Desmodesmus sp. F51. It was found that a nitrogen-sufficient condition was required for lutein accumulation, while a high light intensity enhanced cell growth but caused a decrease in the lutein content. The best cell growth and lutein production occurred when the light intensity and initial nitrate concentration were 600 μmol/m(2)/s and 8.8 mM, respectively. The fed-batch cultivation strategy was shown to further improve lutein production. The highest lutein productivity (3.56±0.10 mg/L/d) and content (5.05±0.20 mg/g) were obtained when pulse-feeding of 2.2 mM nitrate was employed. This study demonstrated the potential of using Desmodesmus sp. F51 as a lutein producer in practical applications.