Biomass and lipid enhancement in Ankistrodesmus sp. cultured with reused and minimal nutrients media

Microalgae are a promising feedstock for biofuel production. Lipid content in microalgae could be enhanced under nutrient depletion. This work investigated the effect of the nutrient on lipid accumulation in Ankistrodesmus sp. culture. Batch cultures were carried out using fresh BG11 medium, and after the harvest, the medium was reused for the next culture; this method was repeated two times. The maximum lipid productivity of 29.75 mg L^?1 day^?1 was obtained from the culture with the second reuse medium. In continuous cultures, Ankistrodesmus sp. was cultured in both fresh and modified BG11 mediums. The modified BG11 medium was adjusted to resemble the content of the first reuse medium. As a comparison between batch and continuous cultures, it was proven that the productivity in the continuous culture was better than in the batch, where the achievable maximum biomass and lipid were 188.30 and 38.32 mg L^?1 day^?1. The maximum lipid content of 34.22% was obtained from the continuous culture at a dilution rate of 0.08 day^?1, whereas the maximum saturated and unsaturated fatty acid productivities of 79.96 and 104.54 mg L^?1 day^?1 were obtained at a dilution rate of 0.16 day^?1.     

Circumtropical distribution of the epiphytic dinoflagellate Coolia malayensis (Dinophyceae): Morphology and molecular phylogeny from Puerto Rico and Brazil

The dinoflagellate genus Coolia, which contains potentially toxic species, is an important component of epiphytic assemblages in marine ecosystems. The morphology of C. malayensis has been illustrated from strains isolated in Asia and Oceania. In this study, strains of C. malayensis isolated from the Caribbean Sea in Puerto Rico, and for the first time from the South Atlantic Ocean in Brazil, were investigated by light, epifluorescence and scanning electron microscopies. No significant morphological differences between these new strains and other geographically distant strains of C. malayensis were observed. In the LSU rDNA phylogeny, the C. malayensis sequences from Brazil and Puerto Rico branched within the clade of strains from Oceania and Asia. The recently described species C. santacroce branched as a sister group of C. monotis, and C. palmyrensis was basal to the combined group of C. monotis/C. malayensis/C. santacroce. A tentative undescribed species from Florida and New Zealand branched as a sister group of C. malayensis. Our results confirm that C. malayensis showed a cosmopolitan distribution in tropical to subtropical waters, while the type species C. monotis remains endemic for the Mediterranean Sea and the temperate North Atlantic.     

Screening of marine microalgae for bioremediation of cadmium-polluted seawater

Twenty four strains out of 191 marine microalgal strains exhibited cadmium (Cd) resistance. They were tested for their Cd removal ability in growth media containing 50 μM Cd. Six strains out of 19 green algae and one out of five cyanobacteria removed more than 10% of total Cd from the medium. The marine green alga Chlorella sp. NKG16014 showed the highest removal of Cd 48.7% of total. Cd removal by NKG16014 was further quantitatively evaluated by measuring the amount of cell adsorption and intracellular accumulation. After 12 days incubation, 67% of the removed Cd was accumulated intracellularly and 25% of the Cd removed was adsorbed on the algal cell surface. The maximum Cd adsorption (q_max) was estimated to be 37.0 mg Cd (g dry cells)⁻¹ using the Langmuir sorption model. The Cd removal by freeze-dried NKG16014 cells was also determined. Cd was more quickly adsorbed by dried cells than that by living cells, with a q_max of 91.0 mg Cd (g dry cells)⁻¹.     

Effects of salinity on cell growth and docosahexaenoic acid content of the heterotrophic marine microalga Crypthecodinium cohnii

The effects of salinity on cell growth and docosahexaenoic acid (DHA) content of three marine microalgal strains, Crythecodinium cohnii ATCC 30556, C. cohnii ATCC 50051 and C. cohnii RJH were investigated. The lag phases of the three strains increased with increasing salinity in Porphyridium medium. The specific growth rate of C. cohnii ATCC 30556 was the highest at 9 g L⁻¹ NaCl while the other two strains had their highest specific growth rates at 5 g L⁻¹ NaCl. The highest cell dry weight concentrations of 2.51 g L⁻¹ and 1.56 g L⁻¹ were achieved at 9 g L⁻¹ NaCl for C. cohnii ATCC 30556 and ATCC 50051, respectively, while the highest dry weight concentration of 2.49 g L⁻¹ was achieved at 5 g L⁻¹ NaCl for C. cohnii RJH. The highest cell growth yield coefficient on glucose was 0.5 g g⁻¹ for both C. cohnii ATCC 30556 and C. cohnii RJH and 0.45 g g⁻¹ for C. cohnii ATCC 50051. All three strains responded to the change of salinity by modifying their cellular fatty acid compositions. At 9 g L⁻¹ NaCl, C. cohnii ATCC 30556 had the highest total fatty acid content and DHA (C22:6) proportion. In contrast, C. cohnii ATCC 50051 and C. cohnii RJH had the highest DHA content at 5 g L⁻¹ NaCl. C. cohnii ATCC 30556 and ATCC 50051 had the highest DHA yield (131.55 and 68.24 mg L⁻¹ respectively) at 9 g L⁻¹ NaCl while C. cohnii RJH had the highest DHA yield (128.83 mg L⁻¹) at 5 g L⁻¹ NaCl. Received 27 May 1999/ Accepted in revised form 27 August 1999     

Characterization of an aerated submerged hollow fiber ultrafiltration device for efficient microalgae harvesting

The present work characterizes a submerged aerated hollow fiber polyvinylidene fluorid (PVDF) membrane (0.03 μm) device (Harvester) designed for the ultrafiltration (UF) of microalgae suspensions. Commercial baker''s yeast served as model suspension to investigate the influence of the aeration rate of the hollow fibers on the critical flux (CF, J _c) for different cell concentrations. An optimal aeration rate of 1.25 vvm was determined. Moreover, the CF was evaluated using two different Chlorella cultures (axenic and non‐axenic) of various biomass densities (0.8–17.5 g DW/L). Comparably high CFs of 15.57 and 10.08 L/m/²/h were measured for microalgae concentrations of 4.8 and 10.0 g DW/L, respectively, applying very strict CF criteria. Furthermore, the J _c‐values correlated (negative) linearly with the biomass concentration (0.8–10.0 g DW/L). Concentration factors between 2.8 and 12.4 and volumetric reduction factors varying from 3.5 to 11.5 could be achieved in short‐term filtration, whereat a stable filtration handling biomass concentrations up to 40.0 g DW/L was feasible. Measures for fouling control (aeration of membrane fibers, periodic backflushing) have thus been proven to be successful. Estimations on energy consumption revealed very low energy demand of 17.97 kJ/m³ treated microalgae feed suspension (4.99 × 10⁻³ kWh/m³) and 37.83 kJ/kg treated biomass (1.05 × 10⁻² kWh/kg), respectively, for an up‐concentration from 2 to 40 g DW/L of a microalgae suspension.     

In vitro culture and conservation of microalgae: Applications for aquaculture, biotechnology and environmental research

Summary Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches, they can occupy extreme habitats ranging from tropical coral reefs to the polar regions, and they contribute to half of the globe’s photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world’s biomass. Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes the central role of culture collections in applied algal research. The second part explores the application of microalgal in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon the exploitation of economically important algal products including aquaculture feed, biomass production for the health care sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing. Throughout the review, emphasis is placed on the application of in vitro techniques for the continued advancement of microalgal research. The paper concludes by assessing future perspectives for the novel application of microalgae and their products.     

产生物柴油微藻培养研究进展

石油的大量使用会导致能源枯竭和温室气体（CO2）排放的增加。为了实现经济和环境的和谐发展,必须使用可再生能源代替石油。可再生能源使用后不会造成温室气体排放的增加。生物柴油是一种理想的可再生能源, 能满足以上要求,所以近年来得到迅速发展。微藻是一种主要利用太阳能固定 CO2,生成制备生物柴油所需油脂的藻类。因此以微藻油脂为原料转化成的生物柴油是石油理想的替代品。简要介绍了产油微藻的种类和微藻油脂的合成,较详细地阐述了微藻自养培养、异养培养、生物反应器、工程微藻的最新研究进展,并初步展望了微藻产油研究的未来发展方向。     

Scaling up microalgal cultures to commercial scale

ABSTRACT

Scaling up algal cultures to the very large volumes required for commercial production is a complex task and requires skilled and experienced personnel. First it is necessary to consider how to optimize the process of producing enough inoculum for the large ponds or photobioreactors in order to minimize the time and cost required. In order to minimize the need for re-inoculation from stock cultures it is also essential to manage the large-scale cultures to avoid significant contamination or collapse. The maintenance of long-term, stable, high-productivity, large-scale cultures, usually under prevailing outdoor conditions of variable irradiance, temperature and rainfall, presents additional challenges most of which are not seen in the constant environment experienced by small-scale laboratory cultures. Methods and protocols to deal with these can only be developed at the large-scale and they will mostly be specific for the alga being cultured, the culture system being used and the location of the production plant. A common feature of all large-scale operations known to us is that, over time (years), both productivity and reliability of the cultures improve as the operators gather experience in managing their cultures.     

Biofouling in photobioreactors for marine microalgae

The economic and/or energetic feasibility of processes based on using microalgae biomass requires an efficient cultivation system. In photobioreactors (PBRs), the adhesion of microalgae to the transparent PBR surfaces leads to biofouling and reduces the solar radiation penetrating the PBR. Light reduction within the PBR decreases biomass productivity and, therefore, the photosynthetic efficiency of the cultivation system. Additionally, PBR biofouling leads to a series of further undesirable events including changes in cell pigmentation, culture degradation, and contamination by invasive microorganisms; all of which can result in the cultivation process having to be stopped. Designing PBR surfaces with proper materials, functional groups or surface coatings, to prevent microalgal adhesion is essential for solving the biofouling problem. Such a significant advance in microalgal biotechnology would enable extended operational periods at high productivity and reduce maintenance costs. In this paper, we review the few systematic studies performed so far and applied the existing thermodynamic and colloidal theories for microbial biofouling formation in order to understand microalgal adhesion on PBR surfaces and the microalgae–microalgae cell interactions. Their relationship to the physicochemical properties of the solid PBR surface, the microalgae cell surfaces, and the ionic strength of the culture medium is discussed. The suitability and the applicability of such theories are reviewed. To this end, an example of biofouling formation on a commercial glass surface is presented for the marine microalgae Nannochloropsis gaditana. It highlights the adhesion dynamics and the inaccuracies of the process and the need for further refinement of previous theories so as to apply them to flowing systems, such as is the case for PBRs used to culture microalgae.