# Static Magnetic Fields Effects on Polysaccharides Production by Different Microsalgae Strains
## 1 Introduction  
Microalgae are a selected group of microorganisms with potential for use in wastewater treatment, increased food quality, besides a high capacity to mitigate atmospheric carbon dioxide (CO\({}_{2}\)). These photosynthetic microorganisms are divided into eukaryotic group (among which the _Chlorophyta_ and the _Rladophyta_ are the most studied phyla), and prokaryotic group containing _Cyanophyllcae_, often called blue-green microalgae. Microalgae have been strongly studied in the last decades, as diversity makes them very attractive to obtain molecules with potential commercial applications, such as pigments, proteins, lipids and polysaccharides. Polysaccharides are high molecular weight macromolecules found in all living organisms [1, 2]. Among them, polysaccharides from microalgae are very promising since these compounds display a large diversity of biochemical structures and functions. They can exhibit many biological activities, as antioxidant [3], antifungal [4], antiparasitic [5] or anticancer [6]. According to the localization and function, thepolysaccharides from microalgae are divided in three groups: structural from cell walls, storage that are intracellular and extracellular polysaccharides. Storage polysaccharides have different structures depending on phyla, e.g., cyanobacteria (including _Spirulina_ and _Arthrospin_ species) synthesize glycogen in the cytosol and chlorophyceae like the microalga _Chlorella fusca_ accumulate amylopectin-like polysaccharides (starch) in the plastid [7; 8; 9; 10], under specific conditions [11; 12]. Such storage carbohydrates can be used as feedstock for bioethanol production [13]. Exopolysaccharides (EPS) are produced by a large number of microalgae and cyanobacteria strains. They can be found released in the culture medium, or remain tightly bound to the membrane, depending on species [1]. Specificity of these macromolecules is the fact that they can contain up to 9-12 different monosaccharides. Moreover, many non-sugar groups are often encountered on the polymer backbone, such as sulphate or methyl groups [1]. In these organisms, EPS synthesis may include several steps, such as the production of activated sugars, their assembly by glycosyltransferases and the export of polymers through the membrane [14]. Currently, new methods to improve and increase the growth and biomolecules production by microalgae have been evaluated, such as the use of static magnetic field (SMF) during the cultivations. SMF has been described to influence or alter the metabolism of microorganisms [15; 16; 17; 18; 19]. For instance, SMF can promote the release of oxygen from algae, enhancing photosynthesis and promoting metabolism and growth [20]. Regarding physical changes, the SMF physically affects paramagnetic and diamagnetic substances in cells that usually affect the biochemical reactions rate, besides changing the growth rate of cells [21]. In a broader sense of biotechnology, the high induction of magnetic field affects some properties of liquids, such as surface tension, density, viscosity, light extinction and wettability of solid substances [22]. Furthermore, the phenomenon of effective penetration of the atmospheric oxygen in solutions pretreated with SMF was already observed. [PERSON] et al. [23] stated that this phenomenon is very interesting since most of microorganisms that degrade organic compounds are aerobic. Therefore, if there is an increase in the oxygen concentration in magnetized liquids, the bacteria growth rate and biodegradation of organic matter are higher. SMF influence has also been shown to be positive in wastewater treatment and sludge management. In all studies involving SMF, the effects depend on the intensity and frequency of the field, type of magnetic field (static or oscillating), the exposure time and the cells conditions [24; 25]. Moreover, this method has advantages, such as its high effectiveness for application to the cultures, its low cost, its non-toxicity to microalgae and is non-interfering with the downstream processes [26].