Biochemical activities in Chlorella sp. and Nannochloropsis salina during lipid and sugar synthesis in a lab-scale open pond simulating reactor

Utilization of dark fermentation effluent for algal cultivation in a modified airlift photobioreactor for biomass and biocrude production

Developing an efficient photobioreactor (PBR) and reducing freshwater dependence are among the significant challenges for generating 3rd generation biomass feedstock. Addressing these, the present study focused on developing a modified airlift (MoAL) PBR. Its performance was further evaluated and compared with the traditional airlift PBR by cultivating microalgae in dark fermentation spent wash. Lower mixing time and higher interfacial mass transfer coefficient was observed in the MoAL PBR having a perforated draft tube. Experimentally, the MoAL exhibited the maximum biomass concentration of 3.18 g L^-1, which was 30% higher than that of the conventional airlift PBR. The semi-continuous operation of the MoAL (with water recycling) achieved the maximum biomass productivity of 0.83 g L^-1 d^-1, two folds superior to that of batch culture. The comprehensive biomass characterization (proximate, ultimate, and thermochemical) further confirmed its potential for bioenergy application. Considering that, hydrothermal liquefaction of the biomass resulted in a maximum biocrude yield of 31% w/w with a higher heating value (HHV) of 36.6 MJ kg^-1. In addition, the biocrude comprised 66.6% w/w lighter fraction (<343 °C), including 21.5% w/w of heavy naphtha, 20.5% w/w of kerosene, and 24.6% w/w of diesel. The results can help develop sustainable technology for simultaneous wastewater remediation and biocrude production.

Critical assessment of protozoa contamination and control measures in mass culture of the diatom Phaeodactylum tricornutum

The diatom Phaeodactylum tricornutum is considered a promising "cell factory" for high-value products fucoxanthin and EPA. But its potential has not been realized due largely to microbial contamination. In this study, seven protozoan strains were identified, of which a heterolobosean amoeba was identified as the most frequently occurring and destructive predator in P. tricornutum culture. The addition of 400 mg L^-1 NH₄HCO₃ inhibited amoeba proliferation with little impact on algal growth. Halting culture mixing at night induced a hypoxia environment that further inhibited amoeba growth. Regardless of culture systems employed, a periodical supply of proper amounts of NH₄HCO₃ alone or in combination with halting culture mixing at night may prevent or treat protozoa contamination in mass culture of P. tricornutum.

Assessing pollen nutrient content: a unifying approach for the study of bee nutritional ecology

Poor nutrition and landscape changes are regularly cited as key factors causing the decline of wild and managed bee populations. However, what constitutes 'poor nutrition' for bees currently is inadequately defined. Bees collect and eat pollen: it is their only solid food source and it provides a broad suite of required macro- and micronutrients. Bees are also generalist foragers and thus the different pollen types they collect and eat can be highly nutritionally variable. Therefore, characterizing the multidimensional nutrient content of different pollen types is needed to fully understand pollen as a nutritional resource. Unfortunately, the use of different analytical approaches to assess pollen nutrient content has complicated between-studies comparisons and blurred our understanding of pollen nutrient content. In the current study, we start by reviewing the common methods used to estimate protein and lipids found in pollen. Next, using monofloral Brassica and Rosa pollen, we experimentally reveal biases in results using these methods. Finally, we use our collective data to propose a unifying approach for analysing pollen nutrient content. This will help researchers better study and understand the nutritional ecology-including foraging behaviour, nutrient regulation and health-of bees and other pollen feeders. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Microalgae Polysaccharides: An Alternative Source for Food Production and Sustainable Agriculture

Carbohydrates or polysaccharides are the main products derived from photosynthesis and carbon fixation in the Calvin cycle. Compared to other sources, polysaccharides derived from microalgae are safe, biocompatible, biodegradable, stable, and versatile. These polymeric macromolecules present complex biochemical structures according to each microalgal species. In addition, they exhibit emulsifying properties and biological characteristics that include antioxidant, anti-inflammatory, antitumor, and antimicrobial activities. Some microalgal species have a naturally high concentration of carbohydrates. Other species can adapt their metabolism to produce more sugars from changes in temperature and light, carbon source, macro and micronutrient limitations (mainly nitrogen), and saline stress. In addition to growing in adverse conditions, microalgae can use industrial effluents as an alternative source of nutrients. Microalgal polysaccharides are predominantly composed of pentose and hexose monosaccharide subunits with many glycosidic bonds. Microalgae polysaccharides can be structural constituents of the cell wall, energy stores, or protective polysaccharides and cell interaction. The industrial use of microalgae polysaccharides is on the rise. These microorganisms present rheological and biological properties, making them a promising candidate for application in the food industry and agriculture. Thus, microalgae polysaccharides are promising sustainable alternatives for potential applications in several sectors, and the choice of producing microalgal species depends on the required functional activity. In this context, this review article aims to provide an overview of microalgae technology for polysaccharide production, emphasizing its potential in the food, animal feed, and agriculture sector.

In-situ transesterification of single-cell oil for biodiesel production: a review

In recent years, biodiesel synthesis and production demands have increased because of its high degradability, cleaner emissions, non-toxicity, and an alternative to petroleum diesel. In this context, Single Cell Oil (SCO) has been identified as an alternative feedstock, having the advantage of accumulating high intracellular lipid. SCO/microbial lipids are potential alternatives for sustainable biodiesel production. The traditional technique for biodiesel production from the oils obtained from microbes generally requires two steps: lipid extraction and transesterification. In-situ transesterification is an innovative and renewable process for biodiesel production. It rules out the need to isolate and refine the feedstock lipid, as it directly uses biomass in a single step, i.e., the pretreated biomass will be subjected to in-situ transesterification in the presence of catalysts. Hence, the production cost can be reduced by eliminating the lipid extraction procedure. The current review focuses on the basic features and advantages of in-situ transesterification of SCO for biodiesel production with the aid of short-chain alcohols along with different acid, base, and enzyme catalysts. In addition, a comparative study was carried out to highlight the merits of in-situ transesterification over conventional transesterification.

Lab-scale photobioreactor systems: principles, applications, and scalability

Phototrophic microorganisms that convert carbon dioxide are being explored for their capacity to solve different environmental issues and produce bioactive compounds for human therapeutics and as food additives. Full-scale phototrophic cultivation of microalgae and cyanobacteria can be done in open ponds or closed photobioreactor systems, which have a broad range of volumes. This review focuses on laboratory-scale photobioreactors and their different designs. Illuminated microtiter plates and microfluidic devices offer an option for automated high-throughput studies with microalgae. Illuminated shake flasks are used for simple uncontrolled batch studies. The application of illuminated bubble column reactors strongly emphasizes homogenous gas distribution, while illuminated flat plate bioreactors offer high and uniform light input. Illuminated stirred-tank bioreactors facilitate the application of very well-defined reaction conditions. Closed tubular photobioreactors as well as open photobioreactors like small-scale raceway ponds and thin-layer cascades are applied as scale-down models of the respective large-scale bioreactors. A few other less common designs such as illuminated plastic bags or aquarium tanks are also used mainly because of their relatively low cost, but up-scaling of these designs is challenging with additional light-driven issues. Finally, this review covers recommendations on the criteria for photobioreactor selection and operation while up-scaling of phototrophic bioprocesses with microalgae or cyanobacteria.

Monitoring lipids profile, CO2 fixation, and water recyclability for the economic viability of microalgae Chlorella vulgaris cultivation at different initial nitrogen

The economic viability of microalgae as a bioenergy source depends on many factors. High CO₂ fixing rate, improved lipids yield, and minimum water footprint are few key parameters. This study investigates the effect of four initial nitrogen concentrations (1-, 2-, 6- and 10-mM as nitrate) on lipids yield, their classification and composition, CO₂ fixation rate, and water quality for further reuse after first cultivation. The initial 6 mM nitrate was found optimum for the growth and overall lipid productivity of Chlorella vulgaris. The maximum quantum efficiency (as Fv/Fm ratio) for algae decreases along with the cell growth profile and depletion of the initial nitrate concentration. CO₂ fixation rate increased initially and peaked during exponential growth and then declined for the rest of the cultivation period. A higher CO₂ fixation rate was recorded at 6 mM, and an overall fixation rate of CO₂ was high at 6 mM. A higher total organic carbon (TOC) is produced in recycled water at a low nitrogen concentration of 1 and 2 mM. TOC changes during the cultivation period and with each reuse of water. Water was recycled twice successfully, while growth was inhibited during the 3rd cycle. Based on all these investigations, 6 mM of initial nitrogen was found optimal at given growth conditions.

Adaptive laboratory evolution principles and applications in industrial biotechnology

Adaptive laboratory evolution (ALE) is an innovative approach for the generation of evolved microbial strains with desired characteristics, by implementing the rules of natural selection as presented in the Darwinian Theory, on the laboratory bench. New as it might be, it has already been used by several researchers for the amelioration of a variety of characteristics of widely used microorganisms in biotechnology. ALE is used as a tool for the deeper understanding of the genetic and/or metabolic pathways of evolution. Another important field targeted by ALE is the manufacturing of products of (high) added value, such as ethanol, butanol and lipids. In the current review, we discuss the basic principles and techniques of ALE, and then we focus on studies where it has been applied to bacteria, fungi and microalgae, aiming to improve their performance to biotechnological procedures and/or inspect the genetic background of evolution. We conclude that ALE is a promising and efficacious method that has already led to the acquisition of useful new microbiological strains in biotechnology and could possibly offer even more interesting results in the future.

Expression of the Vitreoscilla hemoglobin gene in Nannochloropsis oceanica regulates intracellular oxygen balance under high-light

Nannochloropsis oceanica is widely used as a model photosynthetic chassis to produce fatty acids and carotenoid pigments. However, intense light typically causes excessive generation of reactive oxygen species (ROS) and photorespiration in microalgal cells, which results in decreased cell growth rate and unsaturated fatty acid content. In this study, the Vitreoscilla hemoglobin gene (vgb) was introduced into N. oceanica cells and expressed by using the light-harvesting complex promoter and its signal peptide. Compared with wild type (WT), the growth rate of transformants increased by 7.4%-18.5%, and the eicosapentaenoic acid content in an optimal transformant increased by 21.0%. Correspondingly, the intracellular ROS levels decreased by 56.9%-70.0%, and the catalase content in transformants was about 1.8 times that of WT. The photorespiration level of transformants was reduced by the measurement and calculation of the dissolved oxygen concentration under the condition of light-dark transition. The expression level of the key genes related to the photorespiration pathway in transformants was more than 80% lower than that in WT. These results indicated that Vitreoscilla hemoglobin could improve microalgal growth by reducing ROS damage and modulating photorespiration under stress conditions.

Enzymatic Synthesis of Glucose Fatty Acid Esters Using SCOs as Acyl Group-Donors and Their Biological Activities

Sugar fatty acid esters, especially glucose fatty acid esters (GEs), have broad applications in food, cosmetic and pharmaceutical industries. In this research, the fatty acid moieties derived from polyunsaturated fatty acids containing single-cell oils (SCOs) (i.e., those produced from Cunninghamella echinulata, Umbelopsis isabellina and Nannochloropsis gaditana, as well as from olive oil and an eicosapentaenoic acid (EPA) concentrate) were converted into GEs by enzymatic synthesis, using lipases as biocatalysts. The GE synthesis was monitored using thin-layer chromatography, FTIR and in situ NMR. It was found that GE synthesis carried out using immobilized Candida antarctica B lipase was very effective, reaching total conversion of reactants. It was shown that EPA-GEs were very effective against several pathogenic bacteria and their activity can be attributed to their high EPA content. Furthermore, C. echinulata-GEs were more effective against pathogens compared with U. isabellina-GEs, probably due to the presence of gamma linolenic acid (GLA) in the lipids of C. echinulata, which is known for its antimicrobial activity, in higher concentrations. C. echinulata-GEs also showed strong insecticidal activity against Aedes aegypti larvae, followed by EPA-GEs, olive oil-GEs and N. gaditana-GEs. All synthesized GEs induced apoptosis of the SKOV-3 ovarian cancer cell line, with the apoptotic rate increasing significantly after 48 h. A higher percentage of apoptosis was observed in the cells treated with EPA-GEs, followed by C. echinulata-GEs, U. isabellina-GEs and olive oil-GEs. We conclude that SCOs can be used in the synthesis of GEs with interesting biological properties.

A Cyanobacteria-Based Biofilm System for Advanced Brewery Wastewater Treatment

Algal/cyanobacterial biofilm photobioreactors provide an alternative technology to conventional photosynthetic systems for wastewater treatment based on high biomass production and easy biomass harvesting at low cost. This study introduces a novel cyanobacteria-based biofilm photobioreactor and assesses its performance in post-treatment of brewery wastewater and biomass production. Two different supporting materials (glass/polyurethane) were tested to investigate the effect of surface hydrophobicity on biomass attachment and overall reactor performance. The reactor exhibited high removal efficiency (over 65%) of the wastewater’s pollutants (chemical oxygen demand, nitrate, nitrite, ammonium, orthophosphate, and total Kjeldahl nitrogen), while biomass per reactor surface reached 13.1 and 12.8 g·m−2 corresponding to 406 and 392 mg·L−1 for glass and polyurethane, respectively, after 15 days of cultivation. The hydrophilic glass surface favored initial biomass adhesion, although eventually both materials yielded complete biomass attachment, highlighting that cell-to-cell interactions are the dominant adhesion mechanism in mature biofilms. It was also found that the biofilm accumulated up to 61% of its dry weight in carbohydrates at the end of cultivation, thus making the produced biomass a suitable feedstock for bioethanol production.

Single Cell Oil (SCO)-Based Bioactive Compounds: I-Enzymatic Synthesis of Fatty Acid Amides Using SCOs as Acyl Group Donors and Their Biological Activities

Fatty acid amides (FAAs) are of great interest due to their broad industrial applications. They can be synthesized enzymatically with many advantages over chemical synthesis. In this study, the fatty acid moieties of lipids of Cunninghamella echinulata ATHUM 4411, Umbelopsis isabellina ATHUM 2935, Nannochloropsis gaditana CCAP 849/5, olive oil, and an eicosapentaenoic acid (EPA) concentrate were converted into their fatty acid methyl esters and used in the FAA (i.e., ethylene diamine amides) enzymatic synthesis, using lipases as biocatalysts. The FAA synthesis, monitored using in situ NMR, FT-IR, and thin-layer chromatography, was catalyzed efficiently by the immobilized Candida rugosa lipase. The synthesized FAAs exhibited a significant antimicrobial activity, especially those containing oleic acid in high proportions (i.e., derived from olive oil and U. isabellina oil), against several human pathogenic microorganisms, insecticidal activity against yellow fever mosquito, especially those of C. echinulata containing gamma-linolenic acid, and anticancer properties against SKOV-3 ovarian cancer cell line, especially those containing EPA in their structures (i.e., EPA concentrate and N. gaditana oil). We conclude that FAAs can be efficiently synthesized using microbial oils of different fatty acid composition and used in specific biological applications.

An untargeted metabolomic approach for the putative characterization of metabolites from Scenedesmus obliquus in response to cadmium stress

Cadmium (Cd) is a widespread contaminant in aquatic systems and has a variety of toxicological implications on freshwater microorganisms. In this study, the green algae Scenedesmus obliquus was exposed to increasing Cd concentrations that inhibited growth by 20% (12.6 μmol L^-1), 30% (39.8 μmol L^-1) and 40% (83.2 μmol L^-1) and the metabolite profiles of released and cellular biomolecules were explored using an untargeted direct infusion high resolution Fourier transform ion cyclotron resonance mass spectrometry approach. In Cd untreated cultures, intrinsic differences in composition existed between released biomolecules and freeze-dried cells. Based on putatively characterized compound groups, a greater proportion of Cys-GSH isomers and carboxyamides were present in exudates whereas sugar isomers and phosphonic acids comprised most cellular metabolites. In cultures exposed to 83.2 μmol L^-1 Cd, an overall shift in metabolomic response across both released biomolecules and cellular components resulted in an increase of lipid-based esters, and Cys-GSH isomers. These two important metabolites are used in antioxidant defense mechanisms and reactive oxygen species prevention during cellular stress. The diversity of metabolites also decreased as Cd concentrations increased when compared to untreated cultures, suggesting that overall metabolites specialize upon metal stress. We show systemic shifts from sugar and carboxylic isomers to specialized proteins and lipid isomers to help S. obliquus cope with stress. These findings highlight the potential use of this green algae as a potential biosorbent and sheds light into the metabolomics of Cd toxicology and insights into microbial metal adaptation.

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. On the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

Microbial sources of polyunsaturated fatty acids (PUFAs) and the prospect of organic residues and wastes as growth media for PUFA-producing microorganisms

The discovery of non-fish sources of polyunsaturated fatty acids (PUFAs) is of great biotechnological importance. Although various oleaginous microalgae and fungi are able of accumulating storage lipids (single cell oils - SCOs) containing PUFAs, the industrial applications utilizing these organisms are rather limited due to the high-fermentation cost. However, combining SCO production with other biotechnological applications, including waste and by-product valorization, can overcome this difficulty. In the current review, we present the major sources of fungi (i.e. members of Mucoromycota, fungoid-like Thraustochytrids and genetically modified strains of Yarrowia lipolytica) and microalgae (e.g. Isochrysis, NannochloropsisandTetraselmis) that have come recently to the forefront due to their ability to produce PUFAs. Approaches adopted in order to increase PUFA productivity and the potential of using various residues, such as agro-industrial, food and aquaculture wastes as fermentation substrates for SCO production have been considered and discussed. We concluded that several organic residues can be utilized as feedstock in the SCO production increasing the competitiveness of oleaginous organisms against conventional PUFA producers.

Two-step treatment of brewery wastewater using electrocoagulation and cyanobacteria-based cultivation

This study combines electrocoagulation (EC) and cyanobacteria-based cultivation for the two-step treatment of brewery wastewater (BW), with the aim to develop a viable alternative to conventional activated sludge technology. The first step applied EC as a pretreatment method, using different electrode materials (aluminum and iron), to remove color and some pollutant load from the BW. After 30 min of EC treatment, decolorization of BW exceeded 80% for both electrode materials and a 100% reduction of total suspended solids was achieved. In the second step, the electrochemically pretreated BW was used as substrate for a cyanobacteria-based cultivation. After 15 days of cultivation total biomass concentrations (containing up to 50% carbohydrates) reached 525.0 mg L^-1 and 740.0 mg L^-1, for aluminum- and iron-pretreated BW, respectively. Moreover, the cyanobacterial community assimilated most of the residual aluminum and iron produced by the EC process, therefore verifying its bioremediation abilities. The combined process also proved effective at pollutant removal (89.1%, 100%, 89.4%, 98.5% and 91.6% of nitrate, ammonium, total Kjeldahl nitrogen, total phosphorus and chemical oxygen demand, respectively). The two-stage treatment method proposed could offer a promising alternative to conventional BW treatment technologies as it combines both efficiency and sustainability.

High-added value products from microalgae and prospects of aquaculture wastewaters as microalgae growth media

Aquaculture plays an important role in human nutrition and economic development but is often expanded to the detriment of the natural environment. Several research projects, aimed at cultivating microalgae in aquaculture wastewaters (AWWs) to reduce organic loads and minerals, along with the production of microalgal cell mass and metabolic products, are underway. Microalgal cell mass is of high nutritional value and is regarded as a candidate to replace, partially at least, the fish meal in the fish feed. Also, microalgal cell mass is considered as a feedstock in the bio-fuel manufacture, as well as a source of high-added value metabolic products. The production of these valuable products can be combined with the reuse of AWWs in the light of environmental concerns related with the aquaculture sector. Many research papers published in the last decade demonstrate that plenty of microalgae species are able to efficiently grow in AWWs, mainly derived from fish and shrimp farms, and produce valuable metabolites reducing the AWW pollutant load. We conclude that bio-remediation of AWWs combining with the production of microalgae cell mass and specific metabolites is probably the most convenient and economical solution for AWWs management and can contribute to the sustainable growth of the aquaculture.

An Overview of Potential Oleaginous Microorganisms and Their Role in Biodiesel and Omega-3 Fatty Acid-Based Industries

Microorganisms are known to be natural oil producers in their cellular compartments. Microorganisms that accumulate more than 20% w/w of lipids on a cell dry weight basis are considered as oleaginous microorganisms. These are capable of synthesizing vast majority of fatty acids from short hydrocarbonated chain (C6) to long hydrocarbonated chain (C36), which may be saturated (SFA), monounsaturated (MUFA), or polyunsaturated fatty acids (PUFA), depending on the presence and number of double bonds in hydrocarbonated chains. Depending on the fatty acid profile, the oils obtained from oleaginous microorganisms are utilized as feedstock for either biodiesel production or as nutraceuticals. Mainly microalgae, bacteria, and yeasts are involved in the production of biodiesel, whereas thraustochytrids, fungi, and some of the microalgae are well known to be producers of very long-chain PUFA (omega-3 fatty acids). In this review article, the type of oleaginous microorganisms and their expertise in the field of biodiesel or omega-3 fatty acids, advances in metabolic engineering tools for enhanced lipid accumulation, upstream and downstream processing of lipids, including purification of biodiesel and concentration of omega-3 fatty acids are reviewed.

The potential use of stickwater from a kilka fishmeal plant in Dunaliella salina cultivation

In this study, the possibility of culturing Dunaliella salina in stickwater (SW) as the main effluent of fishmeal plants was evaluated. D. salina was grown in different media obtained by replacing standard Guillard medium (F/2) with SW at 0% (control), 10%, 25%, 50%, 75%, and 100% ratios. The cell density, pigment contents, proximate composition, saponification value, and fatty acids (FAs) profiles were measured for 14 days. SW was collected from a kilka fishmeal factory in northern Iran, and the characteristics indicated high concentrations of nitrate (242.00 mg L^-1) and phosphate (11.13 mg L^-1). A significant increase in the cell density was observed in 14 days when 75% SW was used. Moreover, SW significantly affected the pigment contents. The highest contents of chlorophylls, total carotenoids, and β-carotene (3.64 μg mL^-1) were calculated in 75% SW. According to the algal proximate composition, the highest and lowest contents of lipid were accumulated in 75% and 100% SW, respectively (p < 0.05). The highest level of saturated FAs was observed in 75% SW compared with the others (p < 0.05). In conclusion, replacing F/2 with SW indicated the capability of D. salina to grow in a treated medium with 75% SW substitution as a bioremediator.

Bioethanol production from microalgae polysaccharides

The worldwide growing demand for energy permanently increases the pressure on industrial and scientific community to introduce new alternative biofuels on the global energy market. Besides the leading role of biodiesel and biogas, bioethanol receives more and more attention as first- and second-generation biofuel in the sustainable energy industry. Lately, microalgae (green algae and cyanobacteria) biomass has also remarkable potential as a feedstock for the third-generation biofuel production due to their high lipid and carbohydrate content. The third-generation bioethanol production technology can be divided into three major processing ways: (i) fermentation of pre-treated microalgae biomass, (ii) dark fermentation of reserved carbohydrates and (iii) direct "photo-fermentation" from carbon dioxide to bioethanol using light energy. All three technologies provide possible solutions, but from a practical point of view, traditional fermentation technology from microalgae biomass receives currently the most attention. This study mainly focusses on the latest advances in traditional fermentation processes including the steps of enhanced carbohydrate accumulation, biomass pre-treatment, starch and glycogen downstream processing and various fermentation approaches.

Characterization and optimization of endogenous lipid accumulation in Chlorella vulgaris SDEC-3M ability to rapidly accumulate lipid for reversing nightly lipid loss

BACKGROUND

During inevitable light/dark cycle, lipid productivity of outdoor microalgae photoautotrophic cultivation is lowered by nightly biomass and lipid loss. To minimize, or even reverse the nightly lipid loss, it was expected that lipid accumulation would not cease, even if at night. Without relying on photosynthesis and organic matter in media, endogenous lipid accumulation that consumes energy and carbon sources derived from cells themselves, namely endogenous accumulation, is the only way for lipid production. The main aims of the present study was to characteristic endogenously accumulated lipid, confirm feasibility to reverse nightly lipid loss, and determine optimal conditions and its quality suitability for biodiesel feedstock production under stress conditions.

RESULTS

Chlorella vulgaris SDEC-3M ability to rapidly accumulated lipid under stress conditions was cultivated for 12 h in darkness, and the effects of various conditions on lipid accumulation and biomass loss were analyzed. Under non-stress conditions, lipid contents dropped. Under certain stress conditions, conversely, the lipid contents were substantially improved so that net nightly endogenous lipid accumulation was observed. Under the optimal conditions (aeration mode with 0.10 vvm and 15% CO₂, 5-10 mg L^-1 of NO₃ ^--N, 30-35 °C, approximate 2500 mg L^-1 of biomass), the lipid content was doubled and increased lipid was approximately 180 mg L^-1. Among stress conditions, N-deficiency had the most significant effect on endogenous lipid accumulation, and the optimum results were characterized under relatively low-N concentrations. Higher consistency between loss in carbohydrate and gain in lipid confirmed accumulated lipid endogenously conversed from carbohydrate. Based on the analyses of fatty acids profiles and prediction of kinematic viscosity, specific gravity, cloud point, cetane number and iodine value, it was confirmed that the quality of lipid obtained under optimal conditions complied with biodiesel quality standards.

CONCLUSION

Via triggering endogenous lipid accumulation by stress conditions, even in darkness, SDEC-3M can synthesize enough lipid suitable for biodiesel feedstock. It implies that the lipid accumulation phase in two-phase strategy can be scheduled at night, and following biomass production stage in light, which should be a solution to improve the lipid yield and quality of large-scale outdoor photoautotrophic microalgae cultivation for biodiesel production.

Sources of microbial oils with emphasis to Mortierella (Umbelopsis) isabellina fungus

The last years a constantly rising number of publications have appeared in the literature in relation to the production of oils and fats deriving from microbial sources (the "single cell oils"-SCOs). SCOs can be used as precursors for the synthesis of lipid-based biofuels or employed as substitutes of expensive oils rarely found in the plant or animal kingdom. In the present review-article, aspects concerning SCOs (economics, biochemistry, substrates, technology, scale-up), with emphasis on the potential of Mortierella isabellina were presented. Fats and hydrophilic substrates have been used as carbon sources for cultivating Zygomycetes. Among them, wild-type M. isabellina strains have been reported as excellent SCO-producers, with conversion yields on sugar consumed and lipid in DCW values reported comparable to the maximum ones achieved for genetically engineered SCO-producing strains. Lipids produced on glucose contain γ-linolenic acid (GLA), a polyunsaturated fatty acid (PUFA) of high dietary and pharmaceutical importance, though in low concentrations. Nevertheless, due to their abundance in oleic acid, these lipids are perfect precursors for the synthesis of 2nd generation biodiesel, while GLA can be recovered and directed to other usages. Genetic engineering focusing on over-expression of Δ6 and Δ12 desaturases and of C16 elongase may improve the fatty acid composition (viz. increasing the concentration of GLA or other nutritionally important PUFAs) of these lipids.

Comprehensive characterization of microalgal isolates and lipid-extracted biomass as zero-waste bioenergy feedstock: An integrated bioremediation and biorefinery approach

The present study investigated the feasibility of domestic sewage wastewater (DSW) as an alternate to fresh-water microalgae growth media towards high-value bioenergy feedstock production. Eight native microalgal strains were screened from DSW and the effect of raw DSW (RDSW), and autoclaved DSW (ADSW) on growth and bioremediation potential were evaluated and compared with control BG11 medium. The study confirmed RDSW as a potential growth medium while Monoraphidium sp. KMC4 showed superior biomass (1.47 ± 0.08 g L^-1) and lipid yield (436.01 ± 0.06 mg L^-1). The corresponding values for bioremediation of ammonia, nitrate, phosphate, as well as COD remained within 88-100%. CHNS, biochemical, TGA, FTIR, FAME analysis of KMC4 confirmed it's potential as bioenergy feedstock. Additionally, a comprehensive characterization of lipid-extracted microalgae biomass (LEMB) was carried out which suggested that LEMB can be used as a growth promoter as well as feedstock for biogas, bioethanol, and bio-oil production.

Effect of oil spill stress on fatty acid stable carbon isotope composition of Ulva pertusa

Petroleum is one of the most important pollutants in the marine ecosystem, and oil spills have a long-term effect on the marine environment. After an oil spill, petroleum continues to diffuse, flowing to the intertidal zone where it accumulates. Ulva pertusa is the main macroalgae species in the intertidal zone of the ocean, and petroleum is toxic to marine macroalgae. Fatty acids, which are involved in various physiological activities, including metabolism, are indispensable substances in organisms. Thus, an organism's fatty acid composition reflects its physiological state. Because fatty acids are carbon-rich compounds, their stable carbon isotope composition can be measured to assess the state of the organism. In this study, the effects of the water accommodated fraction (WAF) of different concentrations of 180# fuel oil and 0# diesel oil on the chlorophyll a and fatty acid carbon stable isotope composition (δ¹³C_FAs) of U. pertusa were assessed. The fatty acid carbon stable isotope value varied among the different petroleum treatments, and high WAF concentrations significantly inhibited the synthesis of unsaturated fatty acids. Thus, exposure to petroleum products affected the synthesis of fatty acids in U. pertusa and also caused carbon stable isotope fractionation during the fatty acid synthesis process. The results indicate that the saturated fatty acid δ¹³C_16:0 and the unsaturated fatty acid δ¹³C_18:1 can be used as biomarkers to evaluate the degree of petroleum-induced stress in U. pertusa and that carbon stable isotope analysis of U. pertusa can be used as an environmental risk assessment tool in the intertidal zone.

The lipid biochemistry of eukaryotic algae

Algal lipid metabolism fascinates both scientists and entrepreneurs due to the large diversity of fatty acyl structures that algae produce. Algae have therefore long been studied as sources of genes for novel fatty acids; and, due to their superior biomass productivity, algae are also considered a potential feedstock for biofuels. However, a major issue in a commercially viable "algal oil-to-biofuel" industry is the high production cost, because most algal species only produce large amounts of oils after being exposed to stress conditions. Recent studies have therefore focused on the identification of factors involved in TAG metabolism, on the subcellular organization of lipid pathways, and on interactions between organelles. This has been accompanied by the development of genetic/genomic and synthetic biological tools not only for the reference green alga Chlamydomonas reinhardtii but also for Nannochloropsis spp. and Phaeodactylum tricornutum. Advances in our understanding of enzymes and regulatory proteins of acyl lipid biosynthesis and turnover are described herein with a focus on carbon and energetic aspects. We also summarize how changes in environmental factors can impact lipid metabolism and describe present and potential industrial uses of algal lipids.

Molecular profiling of an oleaginous trebouxiophycean alga Parachlorella kessleri subjected to nutrient deprivation for enhanced biofuel production

BACKGROUND

Decreasing fossil fuels and its impact on global warming have led to an increasing demand for its replacement by sustainable renewable biofuels. Microalgae may offer a potential feedstock for renewable biofuels capable of converting atmospheric CO₂ to substantial biomass and valuable biofuels, which is of great importance for the food and energy industries. Parachlorella kessleri, a marine unicellular green alga belonging to class Trebouxiophyceae, accumulates large amount of lipids under nutrient-deprived conditions. The present study aims to understand the metabolic imprints in order to elucidate the physiological mechanisms of lipid accumulations in this microalga under nutrient deprivation.

RESULTS

Molecular profiles were obtained using gas chromatography-mass spectrometry (GC-MS) of P. kessleri subjected to nutrient deprivation. Relative quantities of more than 60 metabolites were systematically compared in all the three starvation conditions. Our results demonstrate that in lipid metabolism, the quantities of neutral lipids increased significantly followed by the decrease in other metabolites involved in photosynthesis, and nitrogen assimilation. Nitrogen starvation seems to trigger the triacylglycerol (TAG) accumulation rapidly, while the microalga seems to tolerate phosphorous limitation, hence increasing both biomass and lipid content. The metabolomic and lipidomic profiles have identified a few common metabolites such as citric acid and 2-ketoglutaric acid which play significant role in diverting flux towards acetyl-CoA leading to accumulation of neutral lipids, whereas other molecules such as trehalose involve in cell growth regulation, when subjected to nutrient deprivation.

CONCLUSIONS

Understanding the entire system through qualitative (untargeted) metabolome approach in P. kessleri has led to identification of relevant metabolites involved in the biosynthesis and degradation of precursor molecules that may have potential for biofuel production, aiming towards the vision of tomorrow's bioenergy needs.

Emerging techniques for cell disruption and extraction of valuable bio-molecules of microalgae Nannochloropsis sp

Microalgae of Nannochloropsis sp. present valuable source of bio-molecules (pigments, lipids, proteins) that have nutritional potential for the prevention and treatment of human diseases. Moreover, some species of Nannochloropsis are the promising sources of biofuels and excellent candidates for the replacement of classical biofuel crops. This review describes and compares the efficiency of different conventional and novel techniques that can be used for cell disruption and recovery of bio-molecules from Nannochloropsis sp. Classification of different extraction techniques includes chemical, enzymatic, mechanical and other physical methods. The detailed analysis of extraction efficiency assisted by pressure and temperature (subcritical and supercritical fluids, hydrothermal liquefaction), ultrasound, microwaves, and pulsed electric energy (pulsed electric fields and high voltage electrical discharges) is presented. The general discussion includes comparison between techniques, their effectiveness for cell disruption and selectivity of bio-molecules extraction from Nannochloropsis sp. The cost-effectiveness, benefits and limitations of different techniques are also analyzed.

Agroindustrial Wastewater Treatment with Simultaneous Biodiesel Production in Attached Growth Systems Using a Mixed Microbial Culture

The use of cyanobacteria in biological wastewater treatment technologies can greatly reduce operation costs by combining wastewater bioremediation and production of lipid suitable as biodiesel feedstock. In this work, an attached growth system was employed to achieve the above-mentioned dual objective using a mixed microbial culture dominated by Leptolyngbya and Limnothrix species in diverse heterotrophic consortia. Kinetic experiments on different initial pollutant concentrations were carried out to determine the ability of the established culture to remove organic load (expressed by d-COD, dissolved-Chemical Oxygen Demand), N and P from agroindustrial wastewaters (dairy, winery and raisin). Biomass and oil productivity were determined. It was found that significant removal rates of nutrients were achieved in all the wastewaters examined, especially in that originated from winery in which the highest d-COD removal rate (up to 97.4%) was observed. The attached microbial biomass produced in winery wastewater contained 23.2% lipid/biomass, wt/wt, which was satisfying. The growth in the dairy wastewater yielded the highest attached biomass productivity (5.03 g m−2 day−1) followed by the mixed effluent of winery-raisin (4.12 g m−2 day−1) and the winery wastewater (3.08 g m−2 day−1). The produced microbial lipids contained high percentages of saturated and mono-unsaturated fatty acids (over 89% in total lipids) in all substrates examined. We conclude that the proposed attached growth photobioreactor system can be considered an effective wastewater treatment system that simultaneously produces microbial lipids suitable as biodiesel feedstock.

Fish farm effluents are suitable growth media for Nannochloropsis gaditana, a polyunsaturated fatty acid producing microalga

Fish farm effluents may be used as culture media for marine microalgae, the cell mass of which constitute an excellent fish feed rich in bioactive compounds. In the current investigation different fish farm effluents were tested as culture media for Nannochloropsis strains. Among them, Nannochloropsis gaditana grew well on the effluent released from the sedimentation tank (EST), which is the final step of the wastewater treatment. Mono-algal but non-aseptic cultures were conducted in two types of photo-bioreactors, namely stirred tank reactor (STR) and open pond simulating reactor (OPSR) working under various photoperiods. N. gaditana grew well under full illumination mode on phosphate rich EST in the STR, producing 847.0 mg/L of dry cell mass containing 7.8%, w/w lipids, while when cultivated on phosphate limited EST, cell mass production was slightly lower but lipid biosynthesis was favored, with the lipid content reaching 24.7%, w/w in dry cell mass. In all trials, Nannochloropsis cell mass contained significant quantities of proteins and polysaccharides. Neutral lipids were predominant over polar lipids. Both glycolipid and phospholipid fractions were rich in polyunsaturated fatty acids, especially in eicosapentaenoic acid. We conclude that fish farm wastewaters can be re-used as microalgae growth media, which is of financial and environmental importance.

Application of growth-phase based light-feeding strategies to simultaneously enhance Chlorella vulgaris growth and lipid accumulation

Considering the variations of optimal light intensity required by microalgae cells along with growth phases, growth-phase light-feeding strategies were proposed and verified in this paper, aiming at boosting microalgae lipid productivity from the perspective of light conditions optimization. Experimental results demonstrate that under an identical time-averaged light intensity, the light-feeding strategies characterized by stepwise incremental light intensities showed a positive effect on biomass and lipid accumulation. The lipid productivity (235.49 mg L^-1 d^-1) attained under light-feeding strategy V (time-averaged light intensity: 225 μmol m^-2 s^-1) was 52.38% higher over that obtained under a constant light intensity of 225 μmol m^-2 s^-1. Subsequently, based on light-feeding strategy V, microalgae lipid productivity was further elevated to 312.92 mg L^-1 d^-1 employing a two-stage based light-feeding strategy V₅₆₀ (time-averaged light intensity: 360 μmol m^-2 s^-1), which was 79.63% higher relative to that achieved under a constant light intensity of 360 μmol m^-2 s^-1.

Quantification of Tetradesmus obliquus (Chlorophyceae) cell size and lipid content heterogeneity at single-cell level

Much of our current knowledge of microbial growth is obtained from studies at a population level. Driven by the realization that processes that operate within a population might influence a population's behavior, we sought to better understand Tetradesmus obliquus (formerly Scenedesmus obliquus) physiology at the cellular level. In this work, an accurate pretreatment method to quantitatively obtain single cells of T. obliquus, a coenobia-forming alga, is described. These single cells were examined by flow cytometry for triacylglycerol (TAG), chlorophyll, and protein content, and their cell sizes were recorded by coulter counter. We quantified heterogeneity of size and TAG content at single-cell level for a population of T. obliquus during a controlled standard batch cultivation. Unexpectedly, variability of TAG content per cell within the population increased throughout the batch run, up to 400 times in the final stage of the batch run, with values ranging from 0.25 to 99 pg · cell^-1 . Two subpopulations, classified as having low or high TAG content per cell, were identified. Cell size also increased during batch growth with average values from 36 to 70 μm³  · cell^-1 ; yet cell size variability increased only up to 16 times. Cell size and cellular TAG content were not correlated at the single-cell level. Our data show clearly that TAG production is affected by cell-to-cell variation, which suggests that its control and better understanding of the underlying processes may improve the productivity of T. obliquus for industrial processes such as biodiesel production.

Direct Photosynthetic Production of Plastic Building Block Chemicals from CO2

Hydroxy acids have attracted attention as building block chemicals due to their roles as precursors for the production of various pharmaceuticals, vitamins, antibiotics, and flavor compounds as well as monomers for biodegradable plastic polyesters. The current approach to hydroxy acid production relies on nonrenewable fossil resources such as petroleum for raw materials, raising issues such as the rising costs of starting materials and environmental incompatibility. Recently, synthetic biology approaches based on the rational design and reconstruction of new biological systems were implemented to produce chemicals from a variety of renewable substrates. In addition to research using heterotrophic organic carbon-dependent Escherichia coli or yeasts, photosynthetic microorganisms such as cyanobacteria possessing the ability to absorb solar radiation and fix carbon dioxide (CO₂) as a sole carbon source have been engineered into a new type of microbial cell factory to directly produce hydroxy acids from CO₂. In this chapter, recent progress regarding the direct photosynthetic production of three important hydroxy acids-3-hydroxypropionate (3-HP), 3-hydroxybutyrate (3-HB), and 3-hydroxyvalerate (3-HV)-from CO₂ in cyanobacteria is summarized and discussed.

Phenols recovery after steam explosion of Olive Mill Solid Waste and its influence on a subsequent biomethanization process

A promising source of high added value compounds is the Olive Mill Solid Waste (OMSW). The aim of this research was to evaluate the viability of a biorefinery approach to valorize OMSW through the combination of steam explosion, phenols extraction, and anaerobic digestion. Steam explosion treatment increased the total phenol content in the steam exploited OMSW, which was twice than that the total phenol content in raw OMSW, although some undesirable compounds were also formed. Phenol extraction allowed the recovery of 2098mg hydroxytyrosol per kg of OMSW. Anaerobic digestion allowed the partial stabilization of the different substrates, although it was not improved by the steam explosion treatment. The economic suitability of the proposed biorefinery approach is favorable up to a phenol extract price 90.7% lower than the referenced actual price of 520€/kg.

Applications for Marine Resources in Cosmetics

Marine resources represent an interesting source of active ingredients for the cosmetics industry. Algae (macro and micro) are rich in proteins, amino acids, carbohydrates, vitamins (A, B, and C) and oligo-elements such as copper, iron and zinc. All those active principles play roles in hydration, firming, slimming, shine and protection. Marine organisms inhabit a wide spectrum of habitats. Photo-protective compounds can be obtained from organisms subjected to strong light radiation, such as in tropical systems or in shallow water. In the same way, molecules with antioxidant potential can be obtained from microorganisms inhabiting extreme systems such as hydrothermal vents. For example, marine bacteria collected around deep-sea hydrothermal vents produce complex and innovative polysaccharides in the laboratory which are useful in cosmetics. There are many properties that will be put forward by the cosmetic industries.

Sequential adaptation of Nannochloropsis gaditana to table olive processing water

The main objective of this study was to evaluate the suitability of Nannochloropsis gaditana to grow by sequential adaptation to TOPW (Table olive processing water) at increased substrate concentrations (10-80%). Sequential adaptation allows growing Nannochloropsis gaditana up to 80% TOPW, although the maximum microalgae biomass productions were achieved for percentages of 20-40%, i.e. 0.308 ± 0.005 g VSS (Volatile Suspended Solids)/L. In all growth experiments, proteins were the majority compound in the grown microalgae biomass (0.44 ± 0.05 g/g VSS), whereas phenols were retained up to a mean concentration of 12.1 ± 1.9 mg total phenols/g VSS. The highest microalgae biomass production rate at rate of 80% TOPW took place in the first two days when most nutrients were also removed. Average removal efficiencies at this percentage of TOPW were 69.1%, 50.9%, 54.3% and 71.8% for total organic carbon, total soluble nitrogen, phosphate and total phenols, respectively. Sequential adaptation can ensure the obtaining of a sustainable microalgae culture as a treatment method for TOPW.