Edible Cyanobacterial Genus Arthrospira: Actual State of the Art in Cultivation Methods, Genetics, and Application in Medicine

The cyanobacterial genus Arthrospira appears very conserved and has been divided into five main genetic clusters on the basis of molecular taxonomy markers. Genetic studies of seven Arthrospira strains, including genome sequencing, have enabled a better understanding of those photosynthetic prokaryotes. Even though genetic manipulations have not yet been performed with success, many genomic and proteomic features such as stress adaptation, nitrogen fixation, or biofuel production have been characterized. Many of above-mentioned studies aimed to optimize the cultivation conditions. Factors like the light intensity and quality, the nitrogen source, or different modes of growth (auto-, hetero-, or mixotrophic) have been studied in detail. The scaling-up of the biomass production using photobioreactors, either closed or open, was also investigated to increase the production of useful compounds. The richness of nutrients contained in the genus Arthrospira can be used for promising applications in the biomedical domain. Ingredients such as the calcium spirulan, immulina, C-phycocyanin, and γ-linolenic acid (GLA) show a strong biological activity. Recently, its use in the fight against cancer cells was documented in many publications. The health-promoting action of "Spirulina" has been demonstrated in the case of cardiovascular diseases and age-related conditions. Some compounds also have potent immunomodulatory properties, promoting the growth of beneficial gut microflora, acting as antimicrobial and antiviral. Products derived from Arthrospira were shown to successfully replace biomaterial scaffolds in regenerative medicine. Supplementation with the cyanobacterium also improves the health of livestock and quality of the products of animal origin. They were also used in cosmetic preparations.

Optimization of production of C-phycocyanin and extracellular polymeric substances by Arthrospira sp

The key factors influencing the production of C-phycocyanin (C-PC) and extracellular polymeric substances (EPS) by photoautotrophic culture of Arthrospira sp. were optimized using Taguchi method. Six factors were varied at either three or two levels as follows: light intensity at three levels; three initial culture pHs; two species of Arthrospira; three concentrations of Zarrouk's medium; three rates of aeration of the culture with air mixed with 2% v/v carbon dioxide; and two incubation temperatures. All cultures ran for 14 days. The optimal conditions for the production of C-PC and EPS were different. For both products, the best cyanobacterium proved to be Arthrospira maxima IFRPD1183. The production of C-PC was maximized with the following conditions: a light intensity of 68 µmol photons m^-2 s^-1 (a diurnal cycle of 16-h photoperiod and 8-h dark period), an initial pH of 10, the full strength (100%) Zarrouk's culture medium, an aeration rate of 0.6 vvm (air mixed with 2% v/v CO₂) and a culture temperature of 30 °C. The concentration of Zarrouk's medium was the most important factor influencing the final concentration of C-PC. The optimal conditions for maximal production of EPS were as follows: a light intensity of 203 µmol photons m^-2 s^-1 with the earlier specified light-dark cycle; an initial pH of 9.5; a 50% strength of Zarrouk's medium; an aeration rate of 0.2 vvm (air mixed with 2% v/v CO₂); and a temperature of 35 °C. Production of C-PC and EPS in raceway ponds is discussed.

Ammonia inhibition on Arthrospira platensis in relation to the initial biomass density and pH

In this study the combined effect of total ammoniacal nitrogen (TAN) concentration, initial biomass density and initial pH of the cultivation medium on growth of Arthrospira platensis was studied. The results indicate that TAN inhibition in relation to the initial biomass in unregulated pH cultures is neither a clearly biomass-independent nor biomass-dependent phenomenon. However, low biomass densities are more susceptible to ammonia inhibition than higher biomass densities. Higher biomass densities seems to mitigate ammonia inhibition through rapider assimilation of TAN. In all cases studied the growth rates were lower compared to the cultures with nitrate as nitrogen source. It was observed that at low TAN concentration, although no ammonia inhibition occured the growth rates were decreased due to nitrogen limitation. Low TAN concentration triggered the accumulation of carbohydrates affecting thus significantly the biomass composition. Ammonia losses from the cultivation system were also determined. Ammonia losses ranged between 17% and 80%.

Heavy metal induced antioxidant defense system of green microalgae and its effective role in phycoremediation of tannery effluent

Investigation of tannery effluent toxicology in green microalgae is of great importance from ecological point of view, because heavy metal has become a major contaminant in recent years. The present study determined the effect of various concentrations (0, 10, 25, 50, 75 and 100%) of heavy metals containing tannery effluent on cell growth and antioxidant defense system of two green microalgae. Treatment with effluent induced accumulation of reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). Lower tannery effluent concentrations increased algal growth, whereas higher concentration suppressed the growth and photosynthetic content. Both strains of the microalgae had proven effective in removing heavy metals from aqueous solutions with the highest removal efficiency being near 100% and it can be used for phycoremediation of wastewater in large scale.

Photosynthetic efficiency and rate of CO2 assimilation by Arthrospira (Spirulina) platensis continuously cultivated in a tubular photobioreactor

Similar to other photosynthetic microorganisms, the cyanobacterium Arthrospira platensis can be used to produce pigments, single cell proteins, fatty acids (which can be used for bioenergy), food and feed supplements, and biofixation of CO(2) . Cultivation in a specifically designed tubular photobioreactor is suitable for photosynthetic biomass production, because the cultivation area can be reduced by distributing the microbial cells vertically, thus avoiding loss of ammonia and CO(2) . The aim of this study was to investigate the influence of light intensity and dilution rate on the photosynthetic efficiency and CO(2) assimilation efficiency of A. platensis cultured in a tubular photobioreactor in a continuous process. Urea was used as a nitrogen source and CO(2) as carbon source and for pH control. Steady-state conditions were achieved in most of the runs, indicating that continuous cultivation of this cyanobacterium in a tubular photobioreactor could be an interesting alternative for the large-scale fixation of CO(2) to mitigate the greenhouse effect while producing high protein content biomass.

Two-stage culture method for optimized polysaccharide production in Spirulina platensis

BACKGROUND

The polysaccharides of Spirulina platensis possess many biological functions. Reproducing the conditions under which S. platensis produces polysaccharides is critical to furthering our understanding of the function of these polysaccharides for commercial mass production. The changes in microalgal polysaccharide production were studied under greenhouse and laboratory conditions using varying light intensities, temperatures, and NaCl concentrations.

RESULTS

The polysaccharide yield was positively correlated with culturing under 192 µmol photons m(-2) s(-1) light intensity at 38 °C or in 0.75 mol L(-1) NaCl. However, NaCl reduced the total biomass productivity of S. platensis. To mitigate the negative effects of environmental stress on maximal polysaccharide production, we proposed a two-stage culture method. The first stage, designed to increase biomass production, involved culturing under 96 µmol photons m(-2) s(-1) light intensity at 28 °C. Following this, on achieving maximum biomass production, the second stage, designed to stimulate polysaccharide production, involved culturing under 192 µmol photons m(-2) s(-1) light intensity at 38 °C for 3 days or in a 0.75 mol L(-1) NaCl medium for 2 days. High-performance liquid chromatographic analysis revealed that S. platensis polysaccharides were composed of various monosaccharides, including glucose, galactose, rhamnose, mannose, fructose, and mannitol.

CONCLUSION

The two-stage culture can be successfully applied to achieve the goal of polysaccharide mass production. The first stage focuses on rapidly increasing microalgal biomass. The second stage of culture conditions requires modification to maximize polysaccharide yield.

Influence of ammonium sulphate feeding time on fed-batch Arthrospira (Spirulina) platensis cultivation and biomass composition with and without pH control

Previous work demonstrated that a mixture of NH(4)Cl and KNO(3) as nitrogen source was beneficial to fed-batch Arthrospira (Spirulina) platensis cultivation, in terms of either lower costs or higher cell concentration. On the basis of those results, this study focused on the use of a cheaper nitrogen source mixture, namely (NH(4))(2)SO(4) plus NaNO(3), varying the ammonium feeding time (T=7-15 days), either controlling the pH by CO(2) addition or not. A. platensis was cultivated in mini-tanks at 30°C, 156 μmol photons m(-2) s(-1), and starting cell concentration of 400 mg L(-1), on a modified Schlösser medium. T=13 days under pH control were selected as optimum conditions, ensuring the best results in terms of biomass production (maximum cell concentration of 2911 mg L(-1), cell productivity of 179 mg L(-1)d(-1) and specific growth rate of 0.77 d(-1)) and satisfactory protein and lipid contents (around 30% each).

Effects of light intensity and dilution rate on the semicontinuous cultivation of Arthrospira (Spirulina) platensis. A kinetic Monod-type approach

Semicontinuous cultures were carried out at different dilution rates (D) and light intensities (I) to determine the maximum productivity of Arthrospira platensis cultivated in helicoidal photobioreactor up to the achievement of pseudo-steady-state conditions. At I=108 μmol photons m(-2) s(-1), the semicontinuous regime ensured the highest values of maximum cell concentration (X(m)=5772±113 mg L(-1)) and productivity (P(XS)=1319±25 mg L(-1) d(-1)) at the lowest (D=0.1 day(-1)) and the highest (D=0.3 day(-1)) dilution rates, respectively. A kinetic model derived from that of Monod was proposed to determine the relationship between the product of light intensity to dilution rate (ID) and the cell productivity, which were shown to exert a combined influence on this parameter. This result put into evidence that pseudo-steady-state conditions could be modified according to circumstances, conveniently varying one or other of the two independent variables.

Fed-batch cultivation of Arthrospira (Spirulina) platensis: potassium nitrate and ammonium chloride as simultaneous nitrogen sources

Arthrospiraplatensis was cultivated in minitanks at 13 klux, using a mixture of KNO(3) and NH(4)Cl as nitrogen source. Fed-batch daily supply of NH(4)Cl at exponentially-increasing feeding rate allowed preventing ammonia toxicity and nitrogen deficiency, providing high maximum cell concentration (X(m)) and high-quality biomass (21.85 mg chlorophyll g cells(-1); 20.5% lipids; 49.8% proteins). A central composite design combined to response surface methodology was utilized to determine the relationships between responses (X(m), cell productivity and nitrogen-to-cell conversion factor) and independent variables (KNO(3) and NH(4)Cl concentrations). Under optimum conditions (15.5mM KNO(3); 14.1mM NH(4)Cl), X(m) was 4327 mg L(-1), a value almost coincident with that obtained with only 25.4mM KNO(3), but more than twice that obtained with 21.5mM NH(4)Cl. A 30%-reduction of culture medium cost can be estimated when compared to KNO(3)-batch runs, thus behaving as a cheap alternative for the commercial production of this cyanobacterium.

Effect of cadmium on cellular viability in two species of microalgae (Scenedesmus sp. and Dunaliella viridis)

We determined the effect of several concentrations of cadmium (0, 5, 10, and 20 microg/l) on cellular viability in the microalgae Scenedesmus sp. and Dunaliella viridis, by measuring growth at 0, 24, 48, 72, and 96 h and pigment production at 10 days. Algae were obtained from the Nonvascular Plant Laboratory collection, in the Facultad Experimental de Ciencias, Universidad del Zulia, Venezuela. Growth was measured by cellular counting, while pigment content was evaluated using conventional spectrophotometric techniques. Growth of both species decreased in the exposed cultures comparing with the control, but its behavior was similar, because in both control and exposed cultures, its was observed an adaptive phase in the first hours, as well as a growth phase after 72 h. Cadmium concentrations above 10 microg/l produced an adverse effect on pigment production, depending on the concentration and/or exhibition time. However, even though cadmium inhibited growth and pigment production, levels of both parameters indicated cellular viability, demonstrating the adaptability of the algae cultures when they were exposed to the metal.