Bioprospecting wild South African microalgae as a potential third-generation biofuel feedstock, biological carbon-capture agent and for nutraceutical applications

Microalgae are among the few biological resources studied that are found to possess vast biotechnological potential. This study isolated, identified and investigated two wild green microalgal species with substantial potential as a bioresource and climate change mitigation importance. Two isolates, Chlorella sorokiniana and Tetradesmus reginae were cultivated in selected artificial media under laboratory conditions. The isolates were analysed for nutrient consumption, biomass productivity, CO₂ biosequestration rate, elemental composition and fatty acid methyl profiles/composition. The outcome showed maximum daily biomass productivity of 0.128 ± 0.003 and 0.2 ± 0.004 g L⁻¹ for C. sorokiniana and T. reginae, respectively. CO₂ biosequestration rate of T. reginae was the highest among the isolates, indicating that it can act as a biological climate change mitigation agent. Moreover, T. reginae recorded a significantly higher (p < 0.05) total lipid and carbohydrate content than C. sorokiniana. The C/N ratio for T. reginae was significantly higher than the C/N ratio for C. sorokiniana. Tetradesmus reginae also demonstrated the ability to produce a considerable quantity of omega-3 oils; hence, the species is of nutraceutical importance. Furthermore, T. reginae demonstrated maximal carbohydrate content and is therefore considered a potential feedstock for bioethanol production. Chlorella sorokiniana, on the other hand, showed a remarkable (p < 0.05) protein content making it a potential source for human food and animal feed supplement. Finally, the two isolates met both European and American quality biodiesel standards with exceptional cetane (CN) and iodine numbers (IV).