## 1 Introduction  
Microalgae use light energy and inorganic nutrients to produce oxygen and biomass rich in a diversity of value-added compounds (Figure 1) [1]. They can thrive in almost all environments and can be found in oceans, brackish water, freshwater, rocks, and soils [2]. Microalgal biotechnological historical data go back to the Aztec population, who harvested _Arthrospira_ from lake Texcoco for food purposes [2, 3]. _Arthrospira_ has also been collected by local people surrounding Lake Chad and consumed as a nutritional supplement called \"dihe\" [2]. _Nostoc_ species have been used by the Chinese as a food delicacy and for their properties for hundreds of years [2]. _Arthrospira platensis, Aphanizomenon flosaquae_ var. flosaquae, _Chorella luteoviridis, Chlorella pyrenoidosis, Chlorella vulgaris, and _Auxencholorella prothecoides_ have been on the market as a food or food ingredient and consumed to a significant degree before 15 May 1997 in the European Union market; thus, its access to the market is not subject to the Novel Food Regulation (EU) 2015/2283 [4]. Dried _Tetraselmis chuii, Odontella aurita_, and astaxanthin-rich oleoresin from _Haematococcus pluvialis_ are microalgal products approvedas a novel food and, as the microalgae listed previously, are within the list of microalgae that can be commercialized in the EU [5]. Through Figure 2a, it is possible to visualize that in most European countries, algae farmers mainly produce microalgaeal species belonging to Cyanobacteria and Chlorophyta phyla, except for Belgium (BE), Norway (NO), and Sweden (SE). This is consistent with the microalgae approved for human consumption which belong to Chlorophyta and Cyanophyta phyla, except for _Odontella aurita_, which belongs to Bacilliophyta phylum. Figure 1: Uncovering the potential of a microcalga as a biofactory. C—carbohydrates; P/E—protein/enzymes; L—lipids; V—vitamins; Pig.—pigments. Figure 2: Microalgae production in Europe: (**a**) relative abundance of microalgae at phylum level produced by algae farmers (AT—Austria; BE—Belgium; BC—Bulgaria; CH—Switzerland; CZ—Czech Republic; DE—Germany; DK—Denmark; EE—Estonia; EL—Greece; ES—Spain; FO—Faroo Islands; FR—France; GR—Greenland; HU—Hungary; IC—Iceland; IE—Ireland; IT—Italy; LV—Latvia; NL——the Netherlands; NO—Norway; PT—Portugal; SE—Sweden; UK—the United Kingdom). (**b**) Number of algae farmers against main microalgae phyla and diversity of species exploited. (**c**) Diversity of Chlorophyta species produced by algae farmers. Based on EMODnet database [6]. Health, energy, and human nutrition are the three main applications for microalgal products [7]. However, the energy production from microalgae is experiencing a slow growth compared to other segments [7]. Through Figure 3a, it is possible to observe that both patents and research activities presented an exponential increase between 2004 and 2014. This trend continued for research activities, in contrast to patent publications. These waves of microalgae-related research and development activities are mainly associated with energy-driven trends, and having as the driving force the high crude oil price [8]. After 2015, this driving force was lost due to the development and popularization of electric cars [8]. Figure 3b shows that research activities were mainly focused on the biological sciences before 1990s. From this decade forward, biotechnology-applied microbiology appeared in the main research categories meeting the slight increase in patent and research publications. Through Figure 2b, it is possible to visualize that the divisions comprising the greatest diversity of microalgal species industrially exploited are Chlorophyta (18) and Bacillariophyta (10) phyla. According to [PERSON] et al. [11] most microalgal species considered for biofuel production are either Chlorophyta or Bacillariophyta, which may explain the previous observation. In the north-west European algae strategic initiatives, the bioenergy (e.g., biodiesel) market is the most mentioned.