Effect of light intensity on β-carotene production and extraction by Dunaliella salina in two-phase bioreactors
ABSTRACT Application of two-phase bioreactors is a useful technique for improvement of the productivity of fermentations. Fermentative extraction of the products in situ is performed in this technique. The effect of light intensity on the extraction of beta-carotene from Dunaliella salina, in the fermentative extraction, has been investigated. Three different average light exposures were applied: 1.5 x 10(-8) (low), 2.7 x 10(-8) (intermediate) and 4.5 x 10(-8) (high) micromol s(-1) per cell. Results show that beta-carotene content of the cells increases by increasing the light exposure. Increase in the beta-carotene content of the cells is not necessarily coupled with an increase in the volumetric production of beta-carotene. Final volumetric production is about the same for the three bioreactors. beta-Carotene extraction rate is enhanced by the increase in the light exposure. The results suggest that extraction rate is related to beta-carotene content of the cells and is not essentially related to the volumetric production of beta-carotene. Although the effectiveness of extraction with respect to the light input is comparable for all light intensities applied, increasing the light input per cell leads to a higher volumetric extraction rate. Moreover, extracted beta-carotene stays very pure even so the extraction increased by the increase of light intensity.
- SourceAvailable from: Kavitha M.D.
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- "Carotenoid biosynthesis is governed by the level and activity of carotenoid biosynthesis enzymes. Dunaliella when exposed to stress conditions such as salinity (Fazeli et al. 2006), high light (Hejazi and Wijffels 2003), or nutrient limitation (Raja et al. 2007), two stereoisomers of βcarotene , all-trans and 9-cis may be accumulated reaching up to 10% of the dry cell weight (Ben-amotz et al. 1982). Metabolic inhibitors like glyphosate (amino acid biosynthesis inhibitor), glufosinate ammonium which is also called as basta (glutamine synthase inhibitor in nitrogen metabolism pathway), DCMU (photosynthetic inhibitor), DPA (inhibitor of β-carotene C-4 oxygenase), nicotine (lycopene cyclase inhibitor) and caffeine (cytokinesis inhibitor) were evaluated to study their effect on growth, carotenoid profile and fatty acid profile of the marine micro alga D. bardawil under two different light intensities. "
ABSTRACT: Dunaliella bardawil, a green alga accumulates high amount of β-carotene under stress conditions. This organism has been exploited for β-carotene at industrial scale. In the present work, various metabolic inhibitors like diphenylamine (DPA), nicotine, basta, glyphosate, DCMU [3-(3',4'-dichlophenyl)-1,1-dimethylurea] and caffeine were used in autotrophic medium, to understand their influence on carotenoid biosynthesis. The results indicated that these metabolic inhibitors influenced the production of carotenoids like wise, DPA and basta increased the contents of β-carotene (1.7 fold), glyphosate and DCMU for lutein (2.4 and 2 fold) caffeine for biomass yields (1.1 fold), while nicotine decreased the biomass yield (3.6 fold), β-carotene (2 fold) and lutein (10.5 fold).Journal of Food Science and Technology -Mysore- 12/2013; 50(6):1130-6. DOI:10.1007/s13197-011-0429-6
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- "Dunaliella has been found to be one of the richest natural sources of b-carotene (Hejazi and Wijffels, 2003; Raja et al., 2007; Zhu and Jiang, 2008). Under suitable conditions, Dunaliella can accumulate up to 10% of the dry cell weight of b-carotene (Loeblich, 1974; Jin and Melis, 2003). "
ABSTRACT: The objective of this work was to quantify the kinetic behavior of Dunaliella primolecta (D. primolecta) subjected to controlled fluid flow under laboratory conditions. In situ velocities of D. primolecta were quantified by micron-resolution particle image velocimetry and particle tracking velocimetry. Experiments were performed under a range of velocity gradients and corresponding energy dissipation levels at microscopic scales similar to the energy dissipation levels of natural aquatic ecosystems. An average swimming velocity of D. primolecta in a stagnant fluid was 41 microm/s without a preferential flow direction. In a moving fluid, the sample population velocities of D. primolecta follow a log-normal distribution. The variability of sample population velocities was maximal at the highest fluid flow velocity in the channel. Local fluid velocity gradients inhibited the accrual of D. primolecta by twofold 5 days after the initiation of the experiment in comparison to the non-moving fluid control experiment.Biotechnology and Bioengineering 09/2010; 107(1):65-75. DOI:10.1002/bit.22774
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ABSTRACT: The low productivity of photobioreactors used for production of high-value compounds from microalgae is a big bottleneck in commercialization. "Milking" of microalgae for the production of high-value compounds in which the produced biomass is reused for production can be a solution to overcome this bottleneck.As it was described in Chapter 1 our main aim was to investigate the possible application of a "milking" process using two-phase bioreactors in microalgal biotechnology. We chose b -carotene extraction from Dunaliella salina in a two-phase bioreactor with an aqueous phase and an organic solvent phase as our model system. The goal was to develop an alternative and more efficient process than the commercial production process of b -carotene.In chapter 2 biocompatibility of different solvents with values of log P <sub>octanol</sub> ranging from 3 to 9 for the cells of Dunaliella salina was investigated. Extraction ability of different solvents for both b -carotene and chlorophyll was determined as well. Results showed that solvents having log P <sub>octanol</sub> > 6 can be considered biocompatible for this alga. Moreover, pigment extraction ability of a solvent is inversely dependent on its log P <sub>octanol</sub> value. By increasing the degenerative hydrophobicity the extraction ability for both chlorophyll and b -carotene, decreased. However, this decrease was more pronouned for chlorophyll. Therefore, selective extraction of b -carotene becomes feasible. The b -carotene productivity per cell in a two-phase system with dodecane was the highest observed. Extraction ability of the biocompatible solvents dodecane, tetradecane and hexadecane was similar.Effect of mixing rate which is supposed to lead to the facilitated release of b -carotene from the cells of Dunaliella salina in two-phase bioreactors, was investigated in chapter 3 . Three pairs of bioreactors were inoculated at the same time, operated at 100, 150 and 170 rounds per minute, respectively and illuminated with a light intensity of 700 m mol m <sup>-2</SUP>s <sup>-1</SUP>. Each pair consisted of one bioreactor containing only aqueous phase for the blank and one containing the water phase together with the biocompatible sovent (dodecane). Comparison of the viability and growth of the cells grown under different agitation rates showed that 170 rpm and 150 rpm were just as good as 100 rpm. Presence and absence of the organic phase had also no influence on the viability and growth of the cells. In contrast to the growth rate, the extraction rate of b -carotene was influenced by the stirrer speed. The extraction rate increases at higher stirring rate. The effectiveness of extraction per amount of power in-put was comparable for all the applied mixing rates.In chapter 4 the effect of light intensity on the extraction of b -carotene from Dunaliella salina , in the fermentative extraction, was investigated. Three different average light exposures were applied: 1.5*10 <sup>-8</SUP>(low), 2.7* 10 <sup>-8</SUP>(intermediate) and 4.5* 10 <sup>-8</SUP>(high) m mol s <sup>-1</SUP>cell <sup>-1</SUP>. Results showed that b -carotene content of the cells increases by increasing the light exposure. Increase in the b -carotene content of the cells was not necessarily coupled with an increase in the volumetric production of b -carotene. b -Carotene extraction rate was enhanced by the increase in the light exposure. The results suggest that extraction rate was related to b -carotene content of the cells and was not essentially related to the volumetric productivity of b -carotene. Although the effectiveness of extraction with respect to the light input was comparable for all light intensities applied, increasing the light input per cell leaded to a higher volumetric extraction rate.On the basis of the previous results the "milking" process for b -carotene production was developed and introduced in Chapter 5 . Growth of the cells was performed at low light intensity after which the cells were transferred to the production bioreactor, which was illuminated at a higher light intensity. The second bioreactor was a two-phase bioreactor consisting out of an aqueous and a biocompatible organic phase. In this bioreactor mixing and extraction were performed by re-circulation of the organic phase. The results showed that D. salina stayed viable for a long period (>47 d) in the presence of a biocompatible organic phase at high light intensity. The cell growth, however, was very slow in this situation. b -Carotene could be continuously extracted to the organic phase. The cells kept producing b -carotene and the extracted molecules were substituted by the cells. As a result b -carotene was continuously milked from the cells. The b -carotene extraction efficiency in this system was more than 55%. The productivity of the system was 2.45 mg. m <sup>-2</SUP>.d <sup>-1</SUP>which is much higher than obtained in commercial plants for b -carotene production.Several studies at macro-scale (bioreactors) and micro-scale (using microscopic techniques) were performed for better understanding the mechanism of the extraction process. The results are presented in Chapter 6 . Based on the results two hypothesis were made for the extraction: one of the mechanisms of extraction is transport of the b -carotene globules from the chloroplast to the space between the cell and the chloroplast membranes and subsequently from there to the outside by exo-cytosis. Another possible mode for the extraction could be release of b -carotene from the globules as a result of alterations in the membrane of globules. b -Carotene molecules diffuse from the chloroplast to the space between the cell and the chloroplast membranes and from there to the medium either by diffusion or by exo-cytosis after accumulation in the vesicles.In the last chapter, Chapter 7 , we discuss the approaches which are helpful in answering two following fundamental questions: is it possible to milk all microalgae? And would this technique be suitable for mass production of high-value secondary metabolites? We think to answer these questions the mechanism of extraction and its relation with the production pathway of the target product should be exactly understood. Our previous results and the results of other researches suggest that chemical behavior and molecular structure of the solvent, chemical properties of the product and its location inside the cells and finally physiological behavior of the cell membrane and the cells by themselves are important parameters in a successful milking process. In this chapter we also discuss some other products (astaxanthin, neurotoxins and DHA ) which we think can be milked from microalgae.