Dunaliella biotechnology: methods and applications

The microalga Dunaliella salina is the best commercial source of natural β-carotene. Additionally, different species of Dunaliella can accumulate significant amounts of valuable fine chemicals such as carotenoids, glycerol, lipids, vitamins, minerals and proteins. They also have a large potential for biotechnological processes such as expressing of foreign proteins and treatment of wastewater. In this review, we discussed several biotechnological aspects of the mass cultivation of D. salina like strain selection, carotenoid induction, culture conditions, culture systems and downstream processes. We also discuss several traditional and new applications of the genus.     

Combination of solid phase extraction and a microalgal test system based on pulse-amplitude modulated fluorescence to detect photosystem 11 herbicides up to 0.05 μeq l−1

This note reports a microalgal test system which usesin-vivo chlorophyll a-fluorescence in combination with a solid phase extraction procedure to monitor photosystem II-herbicides in natural waters up to 0.05 g L^–1.     

An optical method for the rapid measurement of micromolar concentrations of nitrate in marine phytoplankton cultures

This method of nitrate determination by ultraviolet absorption spectrometry is based on the measurement of sample absorbance at a single wavelength (220 nm), which was chosen on the basis of the absorption spectra of the main components of artificial seawater in the ultraviolet domain. No reagents are used and no sophisticated instruments are necessary. For standards prepared in artificial seawater, the relationship between absorbance and nitrate concentration is linear up to 500 μmol N L⁻¹ and the detection limit is 1 μmol N L⁻¹. Precision is 1.5%. Urea and amino acids did not interfere at concentrations typical of seawater. The method also measures nitrite, but this interference only becomes important for species which excrete large amounts of nitrite. The method is extremely rapid, simple to implement and does not require the use of toxic chemicals such as cadmium. It should prove useful for monitoring quickly the nitrate concentrations in laboratory cultures of marine phytoplankton. This revised version was published online in July 2006 with corrections to the Cover Date.     

Increased production of eicosapentaenoic acid by Skeletonema costatum cells after decantation at low temperature

Coagulation of Skeletonema costatum biomass was induced at alkaline pH in enriched sea-water to concentrate the microalgal suspensions by decantation. Incubation of the concentrated cultures at 15 °C after return at pH 7.5 preserved cell viability and increased the yield of lipid extraction and the 20:5(n-3) fatty acid content of the diatom biomass.     

Progress in physicochemical parameters of microalgae cultivation for biofuel production

Microalgae have been exploited for biofuel generation in the current era due to its enormous energy content, fast cellular growth rate, inexpensive culture approaches, accumulation of inorganic compounds, and CO₂ sequestration. Currently, research is ongoing towards the advancement of the microalgae cultivation parameters to enhance the biomass yield. The main objective of this study was to delineate the progress of physicochemical parameters for microalgae cultivation such as gaseous transfer, mixing, light demand, temperature, pH, nutrients and the culture period. This review demonstrates the latest research trends on mass transfer coefficient of different microalgae culturing reactors, gas velocity optimization, light intensity, retention time, and radiance effects on microalgae cellular growth, temperature impact on chlorophyll production, and nutrient dosage ratios for cellulosic metabolism to avoid nutrient deprivation. Besides that, cultivation approaches for microalgae associated with mathematical modeling for different parameters, mechanisms of microalgal growth rate and doubling time have been elaborately described. Along with that, this review also documents potential lipid-carbohydrate-protein enriched microalgae candidates for biofuel, biomass productivity, and different cultivation conditions including open-pond cultivation, closed-loop cultivation, and photobioreactors. Various photobioreactor types, the microalgae strain, productivity, advantages, and limitations were tabulated. In line with microalgae cultivation, this study also outlines in detail numerous biofuels from microalgae.     

利用絮凝进行微藻采收的研究进展

微藻可生产不饱和脂肪酸及色素等多种高附加值产品,同时也可用来生产可再生清洁能源如生物柴油等,具有良好的应用前景。但是,目前微藻细胞的采收成本高居不下,已成为限制微藻生物技术大规模应用的重要因素之一。与其他方法相比,絮凝采收成本低、操作简便,是很有应用前景的采收方法。本文综述了国内外利用化学絮凝、物理絮凝及生物絮凝等方法对不同微藻细胞进行采收的研究,重点对生物絮凝方法进行了总结。利用微生物絮凝剂及微藻细胞的自絮凝进行微藻生物量的回收,是微藻采收技术中环境友好、低成本和行之有效的新方法之一。     

EFFECT OF SEASONAL SEA ICE BREAKOUT ON THE PHOTOSYNTHESIS OF BENTHIC DIATOM MATS AT CASEY,ANTARCTICA1

Photosynthesis of marine benthic diatom mats was examined before and after sea ice breakout at a coastal site in eastern Antarctica (Casey). Before ice breakout the maximum under‐ice irradiance was between 2.5 and 8.2 μmol photons·m^?2·s^?1 and the benthic microalgal community was characterized by low E_k (12.1–32.3 μmol photons·m^?2·s^?1), low relETR_max (9.2–32.9), and high alpha (0.69–1.1). After breakout, 20 days later, the maximum irradiance had increased to between 293 and 840 μmol photons·m^?2·s^?1, E_k had increased by more than an order of magnitude (to 301–395 μmol photons·m^?2·s^?1), relETR_max had increased by more than five times (to 104–251), and alpha decreased by approximately 50% (to 0.42–0.68). During the same time interval the species composition of the mats changed, with a decline in the abundance of Trachyneis aspera (Karsten) Hustedt, Gyrosigma subsalsum Van Heurck, and Thalassiosira gracilis (Karsten) Hustedt and an increase in the abundance of Navicula glaciei Van Heurck. The benthic microalgal mats at Casey showed that species composition and photophysiology changed in response to the sudden natural increase in irradiance. This occurred through both succession shifts in the species composition of the mats and also an ability of individual cells to photoacclimate to the higher irradiances.     

重离子诱变创制高产油微拟球藻新品种

以具有产业化前景的微拟球藻Nannochloropsis oceanica OZ-1为实验材料,利用碳重离子进行诱变育种,采用Imaging-PAM和酶标仪进行大规模筛选,最终获得两株高生长速率微拟球藻突变藻株(HP-1和HP-2),进一步分析显示两株突变藻株(HP-1和HP-2)生物量积累较野生型藻株大幅提高,在18d培养末期生物量分别提高了18％和26％,两株突变藻株油脂产率分别为295 mg/(L·d)和275 mg/(L·d),而野生型藻株为247 mg/(L·d).所获两株突变藻株生长速度快、油脂产率高,较野生型藻株优势明显.     

Bioremediation of synthetic high–chemical oxygen demand wastewater using microalgal species Chlorella pyrenoidosa

The microalgal species Chlorella pyrenoidosa was cultivated in synthetic wastewater of initial chemical oxygen demand (COD), nitrate, and phosphate concentrations of 5000, 100, and 40 mg/L, respectively. The aim of the study was to find out the tolerance of microalgae to different COD concentrations and the extent of COD degradation at those concentrations. Three dilutions of wastewater (initial COD concentrations 5000, 3000, and 1000 mg/L) and three inoculum sizes (0.1, 0.2, and 0.3 g/L) were considered for the study. The experimental parameters such as total organic carbon, total inorganic carbon, COD, optical density, total solids, nitrate, and phosphate were measured on a daily basis. Biodegradation kinetics was determined for all cases using first-order reaction and Monod degradation equations. Optimal results showed that up to 90% reduction in TOC was obtained for 1000 COD wastewater while only 38% reduction in total organic carbon (TOC) was achieved for 5000 COD wastewater. Over 95% reduction in nitrate and nearly 90% removal of phosphate were obtained with the lowest microalgal inoculum concentration (i.e., 0.1 g/L) for all COD dilutions. This study showed that microalgal species C. pyrenoidosa can successfully degrade the organic carbon source (i.e., acetate) with significant removal efficiencies for nitrate and phosphate.     

Novel insight into the process of nutrients removal using an algal biofilm: The evaluation of mechanism and efficiency

Eutrophication of water by nutrient pollution remains an important environmental issue. The aim of this study was to evaluate the nutrient uptake capacity of an algal biofilm as a means to treat polluted water. In addition, the study investigated the nutrient removal process. The algal biofilm was able to remove 99% of phosphorus within 24 hours of P addition, with the PO₄-P concentration in inflowing water ranging from 3 to 10 mg L^?1. Different patterns of phosphorus and nitrogen removal were observed. Daily quantity of removed NO₃-N ranged from 2 to 25% and was highly dependent on solar irradiance. Precipitation of phosphorus during the removal process was studied using X-ray diffraction analyses and was not confirmed in the biofilm. The biofilm system we constructed has a high efficiency for phosphorus removal and, therefore, has great potential for integration into wastewater treatment processes.     

A novel polyculture growth model of native microalgal communities to estimate biomass productivity for biofuel production

Native polyculture microalgae is a promising scheme to produce microalgal biomass as biofuel feedstock in an open raceway pond. However, predicting biomass productivity of native polycultures microalgae is incredibly complicated. Therefore, developing polyculture growth model to forecast biomass yield is indispensable for commercial-scale production. This research aims to develop a polyculture growth model for native microalgal communities in the Minamisoma algae plant and to estimate biomass and biocrude oil productivity in a semicontinuous open raceway pond. The model was built based on monoculture growth of polyculture species and it is later formulated using species growth, polyculture factor (k_value), initial concentration, light intensity, and temperature. In order to calculate species growth, a simplified Monod model was applied. In the simulation, 115 samples of the 2014–2015 field dataset were used for model training, and 70 samples of the 2017 field dataset were used for model validation. The model simulation on biomass concentration showed that the polyculture growth model with k_value had a root-mean-square error of 0.12, whereas model validation provided a better result with a root-mean-square error of 0.08. Biomass productivity forecast showed maximum productivity of 18.87 g/m²/d in June with an annual average of 13.59 g/m²/d. Biocrude oil yield forecast indicated that hydrothermal liquefaction process was more suitable with a maximum productivity of 0.59 g/m²/d compared with solvent extraction which was only 0.19 g/m²/d. With satisfactory root-mean-square errors less than 0.3, this polyculture growth model can be applied to forecast the productivity of native microalgae.     

Recycling and reuse of spent microalgal biomass for sustainable biofuels

The use of microalgal biomass (MAB) for biofuel production has been recognized since long. Despite distinct advantages of algal biofuels, however, their sustainability and economic viability is still doubtful. Overall process cost and low energy recovery need to be significantly improved. The use of MAB, after extracting primary fuels in the form of hydrogen, methane, biodiesel and bioethanol, can be one promising route. This algal biomass, collectively termed as spent microalgal biomass (SMAB), contains even up to 70% of its initial energy level and also retains nutrients including proteins, carbohydrates, and lipids. Potential application routes include diet for animals and fish, the removal of heavy metals and dyes from wastewater, and the production of bioenergy (e.g., biofuels and electricity). Unlike whole algae biomass whose applications are relatively well documented, SMAB has been studied only to limited degree. Therefore, this work gives a brief overview of various ways of SMAB applications. An insight into current status, barriers and future prospects on SMAB research is provided. The feasibility of each application is evaluated on the basis of its energy recovery, economic viability, and future perspectives are provided.     

From open ponds to vertical alveolar panels: the Italian experience in the development of reactors for the mass cultivation of phototrophic microorganisms

The need to develop new concepts in reactor design and the growing interest inSpirulina prompted our group to abandon open ponds in the seventies and to focus interest mainly on closed systems. Two substantially different closed photobioreactors have been developed and are at present under investigation in our Research Centre: the tubular photobioreactor (made of rigid or collapsible tubes) and the recently devised vertical alveolar panel (VAP) made of 1.6-cm-thick Plexiglas alveolar sheets.The technical characteristics of the two systems are described and discussed in relation to the main factors which regulate the growth of oxygenic photosynthetic microorganisms in closed reactors.This paper was presented at the Symposium on Applied Phycology at the Fourth International Phycological Congress, Duke University.     

Use of agricultural surpluses for production of biomass by marine microalgae

The marine microalga Phaeodactylum tricornutum was cultivated in semi-continuous culture under mixotrophic conditions with the soluble fractions of potato, rye and wheat flours that had been naturally fermented, at 2% or 4% (w/v). The rye flour produced the highest microalgal cellular density of 90×10⁶ cells.ml^-1 when supplemented with NaNO₃ and NaH₂PO₄. The autotrophic control only gave 57×10⁶ cells.ml^-1. The value of agricultural surpluses, such as rye flour, can therefore be increased by its use in the production of valuable, microalgal biomass which is rich in protein, pigments and fatty acids.     

Antiadhesive property of microalgal polysaccharide extract on the binding of Helicobacter pylori to gastric mucin

The emergence of antibiotic-resistant Helicobacter pylori is of concern in the treatment of H. pylori-associated gastroduodenal diseases. As the organism was reported to bind gastric mucin, we used porcine gastric mucin as substrate to assess the antiadhesive property of polysaccharides derived from Spirulina (PS), a commercially available microalga, against the binding of H. pylori to gastric mucin. Results show that polysaccharides prevented H. pylori from binding to gastric mucin optimally at pH 2.0, without affecting the viability of either bacteria or gastric epithelial cells, thus favouring its antiadhesive action in a gastric environment. Using ligand overlay analysis, polysaccharide was demonstrated to bind H. pylori alkyl hydroperoxide reductase (AhpC) and urease, which have shown here to possess mucin-binding activity. An in vivo study demonstrated that bacteria load was reduced by >90% in BALB/c mice treated with either Spirulina or polysaccharides. It is thus suggested that polysaccharides may function as a potential antiadhesive agent against H. pylori colonization of gastric mucin.     

PHYCOBILIN CONTENT OF THE CONCHOCELIS PHASE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES: RESPONSES TO ENVIRONMENTAL VARIABLES1

Variations of pigment content in the microscopic conchocelis stage of four Alaskan Porphyra species were investigated in response to environmental variables. Conchocelis filaments were cultured under varying conditions of irradiance and nutrient concentrations for up to 60 d at 11°C and 30 psu salinity. Results indicate that conchocelis filaments contain relatively high concentrations of phycobilins under optimal culture conditions. Phycobilin pigment production was significantly affected by irradiance, nutrient concentration, and culture duration. For Porphyra abbottiae V. Krishnam., Porphyra sp., and Porphyra torta V. Krishnam., maximal phycoerythrin (63.2–95.1 mg · g dwt^?1) and phycocyanin (28.8–64.8 mg · g dwt^?1) content generally occurred at 10 μmol photons · m^?2 · s^?1, f/4–f/2 nutrient concentration after 10–20 d of culture. Whereas for Porphyra hiberna S. C. Lindstrom et K. M. Cole, the highest phycoerythrin (73.3 mg · g dwt^?1) and phycocyanin (70.2 mg · g dwt^?1) content occurred at 10 μmol photons · m^?2 · s^?1, f nutrient concentration after 60 d in culture. Under similar conditions, the different species showed significant differences in pigment content. P. abbottiae had higher phycoerythrin content than the other three species, and P. hiberna had the highest phycocyanin content. P. torta had the lowest phycobilin content.