Evaluation of culture conditions of locally isolated Dunaliella salina strain EgeMacc-024

Enhanced β-carotene and Biomass Production by Induced Mixotrophy in Dunaliella salina across a Combined Strategy of Glycerol, Salinity, and Light

Current mixotrophic culture systems for Dunaliella salina have technical limitations to achieve high growth and productivity. The purpose of this study was to optimize the mixotrophic conditions imposed by glycerol, light, and salinity that lead to the highest biomass and β-carotene yields in D. salina. The combination of 12.5 mM glycerol, 3.0 M salinity, and 50 μmol photons m⁻² s⁻¹ light intensity enabled significant assimilation of glycerol by D. salina and consequently enhanced growth (2.1 × 10⁶ cell mL⁻¹) and β-carotene accumulation (4.43 pg cell⁻¹). The saline and light shock induced the assimilation of glycerol by this microalga. At last stage of growth, the increase in light intensity (300 μmol photons m⁻² s⁻¹) caused the β-carotene to reach values higher than 30 pg cell⁻¹ and tripled the β-carotene values obtained from photoautotrophic cultures using the same light intensity. Increasing the salt concentration from 1.5 to 3.0 M NaCl (non-isosmotic salinity) produced higher growth and microalgal β-carotene than the isosmotic salinity 3.0 M NaCl. The mixotrophic strategy developed in this work is evidenced in the metabolic capability of D. salina to use both photosynthesis and organic carbon, viz., glycerol that leads to higher biomass and β-carotene productivity than that of an either phototrophic or heterotrophic process alone. The findings provide insights into the key role of exogenous glycerol with a strategic combination of salinity and light, which evidenced unknown roles of this polyol other than that in osmoregulation, mainly on the growth, pigment accumulation, and carotenogenesis of D. salina.

Mass cultivation of Dunaliella salina in a flat plate photobioreactor and its effective harvesting

Mass cultivation of Dunaliella salina was standardized in a flat plate photobioreactor followed by a vertical flat plate photobioreactor. Maximum biomass productivity (14.95 ± 0.43 mgL^-1d^-1 dry cell weight) was achieved in the latter at inoculum concentration of OD_680nm = 0.1, 100 µmolm^-2s^-1 light illumination and 1.0 L min^-1 aeration. Semicontinuous operation with varying KNO₃ and NaHCO₃ concentrations resulted highest biomass productivity (17.85 ± 0.55 mgL^-1d^-1) at 0.50 mM NaHCO₃ and 15 mM KNO₃. However, maximum lipid (16.36 ± 1.18% dry cell weight) was achieved at 0.75 mM NaHCO₃ and 10 mM KNO₃. Flocculation studies employing potash alum, FeCl₃·6H₂O or pH showed harvesting efficiencies exceeding 90% in 0.75 mM potash alum or FeCl₃·6H₂O or pH 11, but they yielded low concentration factor (<5) and were detrimental (Fv/Fm < 0.50). A combination of 0.50 mM FeCl₃·6H₂O and pH 9 was found as most suitable flocculating strategy with maximum concentration factor (>14) and least damaging (Fv/Fm > 0.54).

Growth profiling, kinetics and substrate utilization of low-cost dairy waste for production of β-cryptoxanthin by Kocuria marina DAGII

The dairy industry produces enormous amount of cheese whey containing the major milk nutrients, but this remains unutilized all over the globe. The present study investigates the production of β-cryptoxanthin (β-CRX) by Kocuria marina DAGII using cheese whey as substrate. Response surface methodology (RSM) and an artificial neural network (ANN) approach were implemented to obtain the maximum β-CRX yield. Significant factors, i.e. yeast extract, peptone, cheese whey and initial pH, were the input variables in both the optimizing studies, and β-CRX yield and biomass were taken as output variables. The ANN topology of 4-9-2 was found to be optimum when trained with a feed-forward back-propagation algorithm. Experimental values of β-CRX yield (17.14 mg l-1) and biomass (5.35 g l-1) were compared and ANN predicted values (16.99 mg l-1 and 5.33 g l-1, respectively) were found to be more accurate compared with RSM predicted values (16.95 mg l-1 and 5.23 g l-1, respectively). Detailed kinetic analysis of cellular growth, substrate consumption and product formation revealed that growth inhibition took place at substrate concentrations higher than 12% (v/v) of cheese whey. The Han and Levenspiel model was the best fitted substrate inhibition model that described the cell growth in cheese whey with an R2 and MSE of 0.9982% and 0.00477%, respectively. The potential importance of this study lies in the development, optimization and modelling of a suitable cheese whey supplemented medium for increased β-CRX production.

The Effects of Light, Temperature, and Nutrition on Growth and Pigment Accumulation of Three Dunaliella salina Strains Isolated from Saline Soil

Background:

Developing algal industries in saline-alkali areas is necessary. However, suitable strains and optimal production conditions must be studied before widespread commercial use.

Objectives:

The effects of light, temperature, KNO₃, and CO(NH₂)₂ on beta-carotene and biomass accumulation were compared and evaluated in order to provide scientific guidance for commercial algal production in northeastern Thailand.

Materials and Methods:

An orthogonal design was used for evaluating optimal conditions for the algal production of three candidate Dunaliella salina strains (KU XI, KU 10 and KU 31) which were isolated from saline soils and cultured in the column photobioreactor.

Results:

The optimal light and temperature for algae growth were 135.3 μmol m^-2 s^-1 and 22°C, while the conditions of 245.6 μmol m^-2 s^-1 and 22°C induced the highest level of beta-carotene production (117.99 mg L^-1). The optimal concentrations of KNO₃, CO(NH₂)₂, and NaHCO₃ for algae growth were 0.5 g L^-1, 0.36 g L^-1, and 1.5 g L^-1, respectively, while 0, 0.12 g L^-1 and 1.5 g L^-1 were best suited for beta-carotene accumulation. The highest beta-carotene rate per cell appeared with the highest light intensity (12.21 pg) and lowest temperature (12.47 pg), and the lowest total beta-carotene content appeared at the lowest temperature (15°C). There was not a significant difference in biomass accumulation among the three Dunaliella strains; however, the beta-carotene accumulation of KU XI was higher than that of the other two strains.

Conclusions:

Light and temperature were both relevant factors that contributed to the growth and beta-carotene accumulation of the three D. salina strains, and NaHCO₃ had significantly positive effects on growth. The degree of impact of the different factors on cell growth was temperature > NaHCO₃ > light intensity > KNO₃ > CO (NH₂)₂ > strains; the impact on beta-carotene accumulation was temperature > light intensity > KNO₃ > CO (NH₂)₂ > strains > NaHCO₃

Process optimization and modeling for the cultivation of Nannochloropsis sp. and Tetraselmis striata via response surface methodology

The aim of this study was to determine the optimal physical process conditions for the cultivation of locally isolated strains of Nannochloropsis sp. and Tetraselmis striata to achieve maximum growth rate. It was essential to evaluate biomass production at different agitation rates, light intensities, and temperature levels. Central composite design and response surface methodology were applied to design the experiments and optimize the cultivation process for Nannochloropsis sp. and T. striata. The specific growth rate of 0.250 d(-1) was obtained for Nannochloropsis sp. cells under the light intensity of 54 μmol photons · m(-2) · s(-1) , at the agitation rate of 151 rpm in 24.5°C. The optimal physical process conditions for T. striata were obtained under the light intensity of 56 μmol photons · m(-2) · s(-1) in 25.5°C at the agitation rate of 151 rpm in 25.5°C, resulting in a specific growth rate of 0.226 d(-1) . The predicted values were justified by the verification tests. Good agreement between the predicted values and the experimental values confirmed the validity of the models for the cultivation of microalgal strains. In this article, the noteworthy result was that temperature was a dominant factor in obtaining high chl-a content for Nannochloropsis sp., whereas the growth of T. striata strongly depended on light exposure.