## 3 Results and Discussion
### Scale-Up and Biomass Production  
Growth assays were performed in PBRs of different volumes and geometry, namely, pilot-scale 0.25-m\({}^{3}\) FP, 2.5-m\({}^{3}\) tubular PBR and industrial-scale 10-m\({}^{3}\) tubular PBR. The biomass productivities, specific growth rates and photosynthetic efficiencies of _C. amblystomatis_ are presented in Table 1. The higher volumetric productivities were achieved in the pilot-scale systems, reaching similar global and maximum productivities (\(p\geq 0.05\)) in the 0.25-m\({}^{3}\) FP (0.07 and 0.27 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\)) and 2.5-m\({}^{3}\) PBR (0.09 and 0.26 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\)). On the other hand, compared to pilot-scale systems, the industrial scale 10-m\({}^{3}\) PBR registered significantly lower global and maximum volumetric productivities of 0.05 and 0.09 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\), respectively (\(p<0.05\)). The obtained volumetric productivities are lower than those previously reported by [PERSON] et al. [34] for _Alikvia (Chlorococcum) littorale_ grown in a horizontal tubular PBR of 0.09-m\({}^{3}\) (0.74 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\) in Oslo, 0.7 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\) in Wageningen, 0.58 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\) in Rio de Janeiro and 0.6 g\(\cdot\)L\({}^{-1}\)-day\({}^{-1}\) in Cadiz). Figure 3: Bayesian inference trees of the family Chlorococcaceae using 18S ribosomal ribonucleleic acid (rRNA) sequences show that the novel isolate (acc. number: MT026583) forms a clade sister to _C. minutum_/_C. aquaticum_ with _C. ellipsoideum_ as an outgroup. Interestingly, the MT026583 sequence is identical to that of _Oophila amblystomatis_, a species that can be either free-living [33] or a salamander egg symbiont [32]. As these results strongly suggest that _O. amblystomatis_ belongs to the genus _Chlorococcum_, it is here proposed that this species should be renamed as _Chlorococcum amblystomatis_ as given in the tree. Moreover, these results confirm previous data suggesting that the genus _Chlorococcum_ can be clearly divided into two macroclades: Stephanosphaerinia and Moewusinia [31]. ML bootstrap values (>50) and BI posterior probabilities (>0.70) are indicated at the respective branches. The accession number of each sequence used is given after the taxonomic classification of each leaf node. However, an opposite trend was found for the areal productivity, where the highest maximum productivity was achieved in the 10-m\({}^{3}\) PBR, reaching 36.56 g\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (\(p<0.05\)). The overall areal productivity was also higher in the 10-m\({}^{3}\) PBR, when compared to the FP (\(p<0.05\)), but without significant differences when compared to the 2.5-m\({}^{3}\) PBR (\(p\geq 0.05\)). _C. amblystomatis_ has shown higher areal productivities in comparison with the same work of [PERSON] et al. [34] (16.6 g\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) in Oslo, 15.7 g\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) in Wageningen, 13.05 g\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) in Rio de Janeiro and 13.5 g\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) in Cadiz). The explanation for the difference between volumetric and areal productivities among systems is due to the geometry of the reactors. As industrial PBRs have a high density of horizontal tubes, the lower tubes receive a lower amount of light irradiance, caused by shadowing, which reduces the volumetric production. Despite this, as the volume of biomass produced in the same area is substantially higher, it results in higher areal productivities. This trend was previously reported for the same PBRs geometry upon the cultivation of _Tetraselmis_ sp. (Chlorophyta) CTP4 [12] and _Phaedactylum tricornutum_ (Bacillariophyta) [35]. Specific growth rates were similar among the different reactors (\(p\geq 0.05\)) and considerably lower compared to that of _A. littorale_ grown in a 0.09-m\({}^{3}\) PBR (from 0.46 day\({}^{-1}\) to 0.62 day\({}^{-1}\)) [34].