## 1 Introduction  
One of the most important points in microalgae culture is the reduction in the cost of biomass production. Despite the numerous properties of microalgae as feedstock for biofuel production and the huge application areas, the costs greatly influence the scale-up and biomass production. Since getting the biomass is the starting point to achieve the main properties of the rich nutritional value of microalgae, a production strategy that results in an increased growth rate is required [1, 2]. On the other hand, producing biomass with high productivity will consequently allow for obtaining extractable compounds with high added value. New technologies may be tested to increase protein concentration and biomass yield in microalgae cultivations, among them, the use of magnetic fields (MFs) [3]. Although this area of study is promising and innovative, it is not well explored. The MF and electromagnetic fields (EMF) in microalgae cultures are being studied both for the biomass production process itself for the improvement of growth kinetics, but also for the downstream processes, such as harvesting and extraction methods [2, 4, 5]. These effects may be observed in different classes of microorganisms, as in microalgae cultures. Among them, cyanobacteria are a large and widespread group of photo-autotrophic microorganisms that combine the ability to perform oxygenic photosynthesis with typical prokaryotic features [6]. _Arthospira platensis_, traditionally known as spirulina, is a blue-green cyanobacterium [7] and is probably the most cultivated photosynthetic microorganism worldwide. In a recent publication [8], phylogenetic analyses based on the 16S rRNA gene has allowed for establishing a new classification of most of the commercially and bank-deposited strains, including the creation of a new genus under the name _Limnospira_. The strain studied in the lab for many years under the name _Arthrospira platensis_[9; 10; 11], from Institut Pasteur Collection (France), has now been reclassified as _Limnospira indica_ PCC8005. These cyanobacteria have a high content of biologically active compounds, with many applications in human and animal nutrition; cosmetics; and the production of high-value molecules for pharmaceuticals with, for example, antioxidants, anti-inflammatory, antiviral, antiparasitic or anticancer effects [12; 13; 14]. Moreover, it can also be considered as a suitable feedstock for bioethanol production due to its high glycogen content [15]. Microalga proteins stand out favorably with conventional sources regarding quality and quantity, demonstrating that microalgae biomass is a promising source of dietary protein [16]. Numerous studies are being conducted to maximize the worldwide _Arthrospira_ biomass production, mainly through focusing on abiotic factors, such as light intensity, temperature, medium composition, pH and salinity, in different cultivation systems [17; 18; 19; 20]. The growing interest in the effects of magnetic or electromagnetic fields in biological systems, along with more efficient technologies, are driving the research and application of electrotechnologies [4; 21]. In this way, effective techniques with electromagnetic biostimulation [2; 22] and static or modulated MF were studied by different authors [4; 5; 23; 24]. The presence of this kind of technology may result in different outcomes and practical applications depending on its characteristics, e.g., configuration, electric current intensity, intensity and treatment duration. Furthermore, for each biological system that is in contact with the magnetic treatment, it will have a different effect [4]. In this sense, the magnetic treatment may be considered a new approach that aims to improve the parameters evaluated in microalgae cultures. However, there are some gaps in these studies because it is difficult to compare previous investigations from one study to another since the heterogeneity of microalgae strains is huge.