Electron beam-induced mutants of microalgae Arthrospira platensis increased antioxidant activity

doi:10.1016/j.jiec.2013.08.039

Journal of Industrial and Engineering Chemistry

Volume 20, Issue 4, 25 July 2014, Pages 1834-1840

https://doi.org/10.1016/j.jiec.2013.08.039 Get rights and content

Abstract

Electron beam accelerators are reliable and durable equipments of produce ionizing radiation, and can be used industrially as a means to modify physical, chemical, or biological properties of commercial products. We used electron beam-induced mutagenesis to generate genetic diversity in the industrial strain of the microalgae Arthrospira platensis (A. platensis). A screen of A. platensis cells that were exposed to high energy (0.2 MeV, 1.2 mA) electron beams revealed 2 mutants, EM240 and EM384, that had increased levels of commercially valuable compounds compared to the parental strain of microalgae without the penalty to growth rate that is observed when other methods are used to increase these parameters. The increase in the levels of biologically active compounds, such as phycocyanin, lipids, phenolic compound, flavonoids and antioxidant enzymes (SOD and POD) in mutant cells resulted in enhanced antioxidant activity. Thus, to our knowledge, our study is the first to show that it is feasible to use electron-beam mutagenesis as a means to produce microalgae mutants that can be screened for high productivity of commercially valuable bioactive compounds for use in industrial processes.

Graphical abstract

Effects of electron beam radiation on microalgae Arthrospira platensis (A. platensis) were investigated and two mutants, EB240 and EB384 by electron beam were analyzed. They had enhanced antioxidant activity compared to the wild type, and this may reflect an enrichment of lipid, antioxidant enzymes, phenolic compounds and phycocyanin content.

Introduction

Considering the increasing need for food, bioenergy, and pharmaceutical and cosmetic compounds, particular attention has been paid for the last decade to sustainable resources that do not compete with the usual food resources. Microalgae are natural sources of biologically and pharmaceutically active compounds. Of particular importance is their ability to convert atmospheric CO₂ into more complex and commercially valuable organic compounds [1]. The use of microalgae, especially cyanobacteria, for antibiotics and pharmacologically active compounds has received ever increasing interest. Development of industrial processes involving the use of microalgae continues to remain a weak point compared to field production, probably because of their typically low growth rate compared to that of other types of microorganism [2]. While the content of nutraceutical and pharmacological compounds in algal strains is very small, current market values for these products are extremely high. The major products are currently commercialized or under consideration for commercial extraction for use in human and animal health. With regard to the use of microalgae as a platform of recombinant proteins, erythropoietin in Phaeodactylum tricornutum has been successfully produced. Microalgae are primary producers of ω3 polyunsaturated fatty acid and it has already been shown that algal oils rich in docohexaenoic acid (DHA) could constitute a substitute to fish oils [3]. The marine diatom P. tricornutum has been widely used as a food organism in aquaculture and is considered as a potential source for eicosapentaenoic acid (EPA) production [4].

Arthrospira platensis (A. platensis) is a filamentous cyanobacteria that is a commercially valuable source of carbohydrates, lipids, proteins, and many phytochemicals (including phycocyanin and chlorophyll) used in the production of biofuels, health foods, animal feed and therapeutics [5]. For example, phycocyanin has been widely used as a natural blue dye in the food and cosmetic industry, and recent studies have assigned hepatoprotective, anti-inflammatory and antioxidant properties to this compound [6], [7].

Microalgae are also considered a viable source of lipids for the production of biodiesel. A challenge of this application is that the conditions that promote most microalgae to produce large amounts of lipids are stressful to the organism, and in general, lead to low growth rates. Thus, the economical production of algal biodiesel will require optimization of the culture conditions for microalgae growth [8], [9].

Several investigations have shown that many plants have antioxidant activities that could be therapeutically beneficial. Furthermore, it has been suggested that the antioxidant potential of plants can be attributed to their phenolic components [10]. However, compare to higher plants, the presence of phenolic compounds in microalgae has been less frequently reported [11].

Many studies have been performed to determine growth conditions that maximize both algal biomass and production of commercially valuable products in microalgal cultures. An alternative approach is to screen microorganisms that have been subjected to random mutagenesis for mutants that produce increased amounts of the desired metabolite [12]. For example, ethyl methane sulfonate-induced mutation was used to generate a mutant strain of the microalgae Nannochloropsis sp. and A. platensis with improved intracellular lipid content [13], [14]. UV-induced mutagenesis was used to generate mutants of the microalgae Pavlova lutheri that produce large amounts of EPA and DHA [15]. Ion beam irradiation was used as mutagen to generate a strain of the fungus Geotrichum robustum that produces high levels of lipids [16].

Until now, the primary commercial processes rely on a few wild type strains and the selection of original strains with a high potential for biotechnology remains a challenge for the industry. However, artificial induction of genetic diversity in a population by using ionizing radiation, such as that produced by an electron beam, can be an effective approach to overcome situations where the usefulness of an organism is limited by the availability of genetic resources in the natural environment. The electron beam can cause chromosomal aberrations and DNA damage that can further result in a large increase in the frequency of mutations [17]. Irradiation-induced mutagenesis has been widely used in plants, because plant tissues maintain excellent cellular integrity at the energies required for mutation [18]. Numerous studies have discussed bioactive compounds in microalgae. However, there are no reports to date regarding increased antioxidative capacity through strain improvement by electron beam. Here, we present the first study using electron beam to generate genetic diversity in microalgae, and show that electron beam irradiation can be used to generate viable mutants of A. platensis with enhanced production of cellular products with antioxidant activity.

Section snippets

Cyanobacteria culture conditions

A. platensis NIES 39 (KCTC AG30033) was obtained from the Biological Resource Center of the Korea Research Institute of Bioscience and Biotechnology (KRIBB, Daejeon, Korea). A. platensis cells were grown in SOT medium (pH 9) at 35 °C and 6000 lux illumination with constant shaking (120 rpm). The composition of SOT medium is as follows [19]: 16.8 g NaHCO₃, 0.5 g K₂HPO₄, 2.5 g NaNO₃, 1 g K₂SO₄, 1 g NaCl, 0.2 g MgSO₄·7H₂O, 0.04 g CaCl₂·2H₂O, 0.01 g FeSO₄·7H₂O, 0.08 g Na₂EDTA, 0.03 mg H₃BO₃, 0.025 mg MnSO₄·7H₂O,

Effect of electron beam irradiation on cell growth of A. platensis

A. platensis cells were exposed to low energy (0.18 MeV, 0.3 mA) and high energy (0.2 MeV, 1.2 mA) electron beams in an electron beam accelerator. Cells exposed to low energy electron beams received radiation doses of 5.4, 21.6, 32.4, 43.2, 54, and 108 kGy; cells exposed to high energy electron beams received doses of 240 and 384 kGy. Morphologically, A. platensis appeared as regular helical coils or spirals (Fig. 1a). Exposure to low energy electron beams did not alter the morphology of A. platensis

Conclusions

In this study, we used electron beam-induced mutagenesis to generate 2 mutant strains of A. platensis that produce high levels of biologically active compounds. These mutants, EM240 and EM384, had enhanced antioxidant activity compared to the parental microalgae, and this may reflect an enrichment of phycocyanin, lipids, phenolic compounds and antioxidant enzymes. A. platensis mutant strains with enhanced lipid accumulation, but without the penalty to cellular growth rate that is observed with

Acknowledgements

This work was supported by grants Korea Institute of Planning & Evaluation for Technology (IPET, Grant No. 112090-03), Republic of Korea.

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Electron beam-induced mutants of microalgae Arthrospira platensis increased antioxidant activity

Abstract

Graphical abstract

Introduction

Section snippets

Cyanobacteria culture conditions

Effect of electron beam irradiation on cell growth of A. platensis

Conclusions

Acknowledgements

J. Biotechnol.

Food Chem. Toxicol.

Biochem. Biophy. Res. Comm.

Bioresour. Technol.

Nutr. Biochem.

Bioresor. Technol.

Algal Res.

Electron. J. Biotechnol.

Bioresour. Technol.

Food Sci. Technol.

Bioresour. Technol.

J. Exp. Mar. Biol. Ecol.

Biofuels

Curr. Pharm. Biotechnol.

Braz. J. Chem. Eng.

Bioenergy Res.