# _Arthrospira platensis_ as a Feasible Feedstock for Bioethanol Production
###### Abstract  
In recent decades and to deal with the scarcity of fossil fuels, many studies have been developed in order to set up a sustainable biofuel production sector. This new sector must be efficient (high productivity), economically profitable (low production costs and therefore acceptable fuel prices), and ethical (low carbon balance, no competition with food resources). The production of bioethanol is based on the fermentation of reserve sugars, accumulated in the form of starch in microalgae and glycogen in cyanobacteria. The advantage of this bioenergy production route lies in the fact that the post-crop fermentation process is at the industrial stage since it has already been tested for many years for the production of bioethanol from agricultural resources. One of the most cultivated cyanobacteria is _Arthrospira_ (\"_Spirulina_\") and its production is also already at industrial scale. Depending on the cultivation conditions, this cyanobacteria is able to accumulate up to 65% DW (dry weight) of glycogen, making it a feasible feedstock for bioethanol production. The aim of this review is to provide a clear overview of these operating conditions for glycogen accumulation.  
cyanobacteria; _Arthrospira_; glycogen  
1  
[PERSON], [PERSON], [PERSON] _Arthrospira platensis_ as a Feasible Feedstock for Bioethanol Production. _Appl. Sci._**2021**, _11_, _6756_.  
[[https://doi.org/10.3309/app11156756](https://doi.org/10.3309/app11156756)]([https://doi.org/10.3309/app11156756](https://doi.org/10.3309/app11156756))  
Academic Editor: [PERSON]  
Received: 30 June 2021  
Accepted: 22 July 2021  
Published: 22 July 2021  
**Published**: **Note**: **Note**: **Note**: **Note**:**:** **phycocyanin among other compounds [16]. It is also consumed worldwide as a dietary supplement and considered as safe. However, attention has to be paid to the chelating properties of Spirulina species, which can lead to the fixation of heavy metals such as Al, Pb, Ba, Ni, Cd [17] or fluoride [18]. Nevertheless, this microorganism is also suitable for biofuel production (3 rd generation) due to its fast growth, all year cultivation, and chemical composition (44.4% carbohydrates, 45% proteins, and 10% lipids and ashes) [19; 20; 21]. Its high carbon sequestration rate can reach 0.92 g/L/d, making it a feasible biofuel feedstock [22; 23]. In this context, the main biofuels produced by this cyanobacterium have been solid biofuel [24], bio-oil [25], and syngas [23]. Nevertheless, in recent years, a new approach has been developed, which is the use of _Arthospira platensis_ storage polysaccharide (i.e., glycogen) for bioethanol production [26; 27].  
Glycogen (\(\alpha\)-1,4 linked glucan) is a polymeric carbohydrate formed of glucose linked through \(\alpha\)-1,4 and \(\alpha\)-1,6 glycosidic bonds. This polysaccharide can be degraded via enzymatic hydrolysis (saccharification) and fermented into bioethanol [28]. This energy-store polysaccharide is mainly formed in _Arthospira platensis_ as a response of nutrient-stressed conditions, and accumulated (up to 70% DW) in granules in the thylakoid membranes [29; 30; 31]. Once conditions are balanced, accumulated glycogen is hydrolyzed to produce energy for cell metabolism. This characteristic of _Arthospira platensis_ can be exploited to induce glycogen production for bioethanol production [32]. Different modifications in culture medium and culture conditions of _Arthospira platensis_ can enhance glycogen production. This review aims to aggregate those operating conditions, allowing glycogen accumulation in order to have a better overview of the feasibility of using _Arthospira_ as a feedstock for bioethanol production.