Acid Tolerant and Acidophilic Microalgae: An Underexplored World of Biotechnological Opportunities

Abstract

Despite their large number and diversity, microalgae from only four genera are currently cultivated at large-scale. Three of those share common characteristics: they are cultivated mainly autotrophically and are extremophiles or tolerate “extreme conditions.” Extreme growth conditions aid in preventing contamination and predation of microalgae, therefore facilitating outdoor cultivation. In search for new extremophilic algae suitable for large-scale production, we investigated six microalgal strains able to grow at pH below 3 and belonging to four genera; Stichococcus bacillaris ACUF158, Chlamydomonas acidophila SAG 2045, and Chlamydomonas pitschmannii ACUF238, Viridiella fridericiana ACUF035 and Galdieria sulphuraria ACUF064 and ACUF074. All strains were cultivated autotrophically at light intensity of 100 and 300 μmol m−2 s−1 and pH between 1.9 and 2.9. The autotrophic biomass productivities were compared with one of the most productive microalgae, Chlorella sorokiniana SAG 211-8K, grown at pH 6.8. The acid tolerant strains have their autotrophic biomass productivities reported for the first time. Mixotrophic and heterotrophic properties were investigated when possible. Five of the tested strains displayed autotrophic biomass productivities 10–39% lower than Chlorella sorokiniana but comparable with other commercially relevant neutrophilic microalgae, indicating the potential of these microalgae for autotrophic biomass production under acidic growth conditions. Two acid tolerant species, S. bacillaris and C. acidophila were able to grow mixotrophically with glucose. Chlamydomonas acidophila and the two Galdieria strains were also cultivated heterotrophically with glucose at various temperatures. Chlamydomonas acidophila failed to grow at 37°C, while G. sulphuraria ACUF64 showed a temperature optimum of 37°C and G. sulphuraria ACUF74 of 42°C. For each strain, the biomass yield on glucose decreased when cultivated above their optimal temperature. The possible biotechnological applications of our findings will be addressed.

High Molecular Weight λ-Carrageenan Improves the Color Stability of Phycocyanin by Associative Interactions

“…Additionally, the apoprotein from aPC is believed to possess an antioxidative character (Eriksen, 2008). Moreover, PC is the only approved blue coloring food within the European Union with some others currently pending approval (Abiusi et al, 2022). Coloring foods provide an excellent solution for appealing colors while meeting customer demands for natural products and they are generally defined as purely physically and nonselctively extracted coloring additives from foodstuff (Carle and Schweiggert, 2016).…”

Reversible adsorption of iridium in lyophilized cells of the unicellular red alga Galdieria sulphuraria

“…These unique characteristics also make Galdieria spp. suitable for biotechnological uses, including the efficient production of biomass, biocrude oil, and benecial compounds such as phycocyanin and oridosides, 13,[16][17][18] as well as efficient wastewater treatment 16,19 and metal recovery. [20][21][22][23][24] Our previous study comparing G. sulphuraria to the green alga Chlorella vulgaris has demonstrated the highly efficient recovery of Au and Pd from acidic solutions.…”

“…These unique characteristics also make Galdieria spp. suitable for biotechnological uses, including the efficient production of biomass, biocrude oil, and beneficial compounds such as phycocyanin and floridosides, 13,16–18 as well as efficient wastewater treatment 16,19 and metal recovery. 20–24…”

Valorisation of buttermilk in mixotrophic and heterotrophic conditions by using the acidophilic strain Galdieria sulphuraria

“…Galdieria sulphuraria is a polyextremophile unicellular microalga able to grow at temperatures up to 56°C and at a pH between 0.5 and 4. Additionally, G. sulphuraria presents a versatile metabolism, growing autotrophically, heterotrophically or mixotrophically (Abiusi et al 2022b).…”

“…However, contamination by bacteria and fungi is a notable issue when the medium contains sources of organic carbon. The cultivation of extremophilic microalgae is a strategy that can prevent the growth of bacteria or other predators, improving the e cacy of microalgae-based treatment (Abiusi et al 2022b).…”