Innovative development of membrane sparger for carbon dioxide supply in microalgae cultures

The present study was aimed to develop a membrane sparger (MS) integrated into a tubular photobioreactor to promote the increase of the carbon dioxide (CO₂) fixation by Spirulina sp. LEB 18 cultures. The use of MS for the CO₂ supply in Spirulina cultures resulted not only in the increase of DIC concentrations but also in the highest accumulated DIC concentration in the liquid medium (127.4 mg L⁻¹ d⁻¹). The highest values of biomass concentration (1.98 g L⁻¹), biomass productivity (131.8 mg L⁻¹ d⁻¹), carbon in biomass (47.9% w w⁻¹), CO₂ fixation rate (231.6 mg L⁻¹ d⁻¹), and CO₂ use efficiency (80.5% w w⁻¹) by Spirulina were verified with MS, compared to the culture with conventional sparger for CO₂ supply. Spirulina biomass in both culture conditions had high protein contents varying from 64.9 to 69% (w w⁻¹). MS can be considered an innovative system for the supply of carbon for the microalgae cultivation and biomass production. Moreover, the use of membrane system might contribute to increased process efficiency with a reduced cost of biomass production.     

Influence of culture conditions on glutathione production by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

A strategy of experimental design using a fractional factorial design (FFD) and a central composite rotatable design (CCRD) were carried out with the aim to obtain the best conditions of temperature (20–30°C), agitation rate (100–300 rpm), initial pH (5.0–7.0), inoculum concentration (5–15%), and glucose concentration (30–70 g/l) for glutathione (GSH) production in shake-flask culture by Saccharomyces cerevisiae ATCC 7754. By a FFD (2^5–2), the agitation rate, temperature, and pH were found to be significant factors for GSH production. In CCRD (2²) was obtained a second-order model equation, and the percent of variation explained by the model was 95%. The results showed that the optimal culture conditions were agitation rate, 300 rpm; temperature, 20°C; initial pH, 5; glucose, 54 g/l; and inoculum concentration, 5%. The highest GSH concentration (154.5 mg/l) was obtained after 72 h of fermentation.     

Update on the application of magnetic fields to microalgal cultures

Coenzyme Q₁₀ (CoQ₁₀) is the main CoQ species in human and is used extensively in food, cosmetic and medicine industries because of its antioxidant properties and its benefit in prophylactic medicine and therapy for a variety of diseases. Among various approaches to increase the production of CoQ₁₀, microbial fermentation is the most effective. As knowledge of the biosynthetic enzymes and regulatory mechanisms modulating CoQ₁₀ production increases, opportunities arise for metabolic engineering of CoQ₁₀ in microbial hosts. In this review, we present various strategies used up to date to improve CoQ₁₀ production and focus on metabolic engineering of CoQ₁₀ overproduction in microbes. General strategies of metabolic engineering include providing sufficient precursors for CoQ₁₀, increasing metabolic fluxes, and expanding storage capacity for CoQ₁₀. Based on these strategies, CoQ₁₀ production has been significantly improved in natural CoQ₁₀ producers, as well as in heterologous hosts.

     

Magnetic treatment of microalgae for enhanced product formation

Static or modulated magnetic fields (MF) may interact with the biological system and affect the metabolism of microorganisms, such as their photosynthetic capacity or synthesis of carbohydrates. Their effects on microorganisms, which can be classified into inhibiting, stimulating and null, may be interpreted as the result of stress that cells undergo, thus, leading to responses through the same mechanisms. Biological effects of exposure to magnetic forces depend on magnetic intensity, frequency and exposure time. Modifications in these parameters may enhance product formation. Effects differ according to the form and application of MF characteristic parameters. Magnetic treatments have the advantages of being convenient and non-toxic, having low running cost, emitting no secondary pollution, enabling wide application and being easily shielded. MF application to the cultivation of microalgae, to improve the production of finished biomolecules, is a simple, inexpensive and powerful process. However, bioeffects of MF on microalgae need to be further investigated because there have currently been very few available reports in the literature. Thus, studies which aim at optimizing parameters involved in MF application must be developed in order to obtain the best conditions for the production of molecules with high economic potential.     

Magnetic fields: biomass potential of Spirulina sp. for food supplement

Bioprocess and Biosystems Engineering - This study evaluated the influence of the magnetic field on the chemical composition of Spirulina sp. LEB 18 and its digestibility and protein solubility....     

Bioprocess strategies for enhancing biomolecules productivity in Chlorella fusca LEB 111 using CO2 a carbon source

The aim of this study was to evaluate the influence of different carbon dioxide (CO₂) concentrations on the distribution of carbon forms in the culture medium and the biomass production and biomolecules productivity of the strain Chlorella fusca LEB 111. In this study, experiments were carried out in which C. fusca cultures were exposed to different CO₂ concentrations, 0.03% (0.08 ml_CO2 ml_medium⁻¹ days⁻¹), 5% (0.18 ml_CO2 ml_medium⁻¹ days⁻¹), and 15% vol/vol CO₂ (0.54 ml_CO2 ml_medium⁻¹ days⁻¹). Among the carbon chemical species distributions in the culture medium, bicarbonate was predominant (94.2–98.9%), with the highest quantitative percentage in the experiment receiving a 15% CO₂ injection. C. fusca LEB 111 cultivated with 15% CO₂ showed the highest biomass productivity (194.3 mg L⁻¹ days⁻¹) and CO₂ fixation rate (390.9 mg L⁻¹ days⁻¹). The carbohydrate productivity in the culture that received 15% CO₂ was 46.2% higher than the value verified for the culture with the addition of CO₂ from the air (0.03% CO₂). In addition, CO₂ concentration providing increases of 0.03–15% to C. fusca cultures resulted in a 31.6% increase in the lipid productivity. These results showed that C. fusca can be used for CO₂ bioconversion and for producing biomass with potential applications for biofuels and bioproducts.     

Different nitrogen sources and growth responses of Spirulina platensis in microenvironments

Spirulina platensis was cultivated, in comparative studies, using several sources of nitrogen. The standard source used (sodium nitrate) was the same as that used in the synthetic medium Zarrouk, whereas the alternative nitrogen sources consisted of ammonium nitrate, urea, ammonium chloride, ammonium sulphate or acid ammonium phosphate. The initial nitrogen concentrations tested were 0.01, 0.03 and 0.05 M in an aerated photobioreactor at 30 °C, with an illuminance of 1900 lux, and 12 h-light/12 h-dark photoperiod over a period of 672 h. Maximum biomass was produced in medium containing sodium nitrate (0.01–0.03–0.05 M), followed by ammonium nitrate (0.01 M) and urea (0.01 M). The final biomass concentrations were 1.992 g l^–1 (0.03 M sodium nitrate), 1.628 g l^–1 (0.05 M sodium nitrate), 1.559 g l^–1 (0.01 M sodium nitrate), 0.993 g l^–1 (0.01 M ammonium nitrate) and 0.910 g l^–1 (0.01 M urea). This suggested that it is possible to utilize nitrogen sources other than sodium nitrate for growing S. platensis, in order to decrease the production costs of scaled up projects.