Short-term deleterious effects of standard isolation and cultivation methods on new tropical freshwater microalgae strains

Algae with potential biotechnological applications in different industries are commonly isolate from the environment in order to obtain pure (axenic) stocks that can be safely stored for long periods of time. To obtain axenic cultures, antibiotics are frequently used, and cryopreservation is applied to keep standing stocks. However, many of these now standard methods were developed using strains coming from pristine-to-low intervened environments and cold-to-temperate regions. Thus, it is still not well understand the potential effect of said methods on the life cycle and biochemical profile of algae isolates from hiper-eutrophic and constant high-temperature tropical regions, which could potentially render them unsuitable for their intended biotechnological application. In this study, we conducted a genetic characterization (18S rRNA) and evaluated the effect of purification (use of the antibiotic chloramphenicol, CPA) and cryopreservation (dimethyl sulfoxide (DMSO)-sucrose mix and Glycerol) on the growth rate and lipid content of four new tropical freshwater algal isolates: Chorella sp. M2, Chlorella sp. M6, Scenedesmus sp. R3, and Coelastrella sp. A2, from the Ecuadorian coast. The genetic characterization showed a clear discrimination between strains. All strains cultured with CPA had a lower growth rate. After cryopreservation Coelastrella sp. A2 did not grow with both methods; Chorella sp. M2, Chlorella sp. M6 and Scenedesmus sp. R3 presented no significant difference in growth rate between the cryopreservants. A significantly higher lipid content was observed in biomass cryopreserved with glycerol in relation to DMSO-sucrose, with Chorella sp. M2 and Chlorella sp. M6 having twice as much in the first treatment. The results highlight the relevance of choosing an appropriate method for storage as the materials used can affect the biological performance of different tropical species, although is still to determine if the effects observed here are long lasting in subsequent cultures of these algae.