Effects of static magnetic field on Chlorella vulgaris : growth and extracellular polysaccharide (EPS) production

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Effects of static magnetic field on Chlorella vulgaris: growth and extracellular polysaccharide (EPS) production Xin Luo 1 & Hao Zhang 1 & Qi Li 1 & Jibiao Zhang 1 Received: 18 December 2019 / Revised and accepted: 26 May 2020 # Springer Nature B.V. 2020

Abstract In this study, Chlorella vulgaris treated with static magnetic field (SMF) was investigated in terms of the algal density, biomass, extracellular polysaccharide content and distribution, percentage of algal aggregation, total protein content, enzyme activity, malondialdehyde content, and nutrient removal. The algal density and biomass under 800 G SMF were highest on the 16th day and were 29.02% and 35.67% greater than the control group (0 G group), respectively. Soluble EPS decreased with an increase in magnetic field strength, while bound EPS exhibited an opposite trend. Algal aggregation occurred in all treatment groups, with the aggregation percentage in the high magnetic field-treated groups being lower than that in the control group. Total protein content of the 800 G group was the lowest at 1.13 μg (106 cells)-1 and the enzyme activity of treated algae was higher than that of the control group. SMF affected the growth and reproduction of C. vulgaris by affecting the antioxidant response. Keywords Static magnetic field . Chlorella vulgaris . Extracellular polysaccharide . Algal density . Aggregation percentage

Introduction Eutrophication of water can cause algal blooms, which in turn causes water quality problems such as malodour and taste issues and algal toxin formation (Chiou et al. 2010; Lee et al. 2014). However, microalgae contain a large amount of oil, which potentially can be used as a source of biofuels, providing a renewable energy source (Schenk et al. 2008; Mata et al. 2010). In addition, microalgae also have many other uses, such as raw materials for cosmetics and animal feed (Markou and Nerantzis 2013). Several studies highlighted the effect of abiotic (i.e., temperature, light, heavy metals, and nutrients concentration) and biotic (i.e., ecological competition) factors on algal growth (Guerrini et al. 2000; Granum et al. 2002; Ghasemi et al. 2009; Widjaja et al. 2009; Rugnini et al. 2018). Aggregation has a great impact on algal and cyanobacterial growth and recycling. It has been reported that, compared with colonial Microcystis, the photosynthetic rate and activity of unicellular Microcystis are lower (Wu and Song 2008). Extracellular polymeric substances contain polysaccharides * Jibiao Zhang [email protected] 1

Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, People’s Republic of China

and other macromolecules such as proteins, lipids, and DNA. In this study, the quantities of extracellular polysaccharides (EPS) were analyzed. EPS can affect the surface charge, structure, flocculation, sedimentation performance, adsorption capacity, and dehydration performance of microbial aggregates (Sheng et al. 2010). In addition, EPSs are the main “cement” in the aggregation of cells and the cell pro