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BACKGROUND: Microalgae biomass is regarded as one of the most promising renewable biomass energy resources with the potential as a sustainable biological climate change mitigation agent, raw material for commercially valuable products and fossil fuel replacement. In view of that, this study isolated, identified and evaluated the potential of an indigenous freshwater green microalga strain, Tetradesmus obliquus UJEA_AD, collected from Emmarentia Dam, Johannesburg, South Africa.RESULTS: Morphological analysis and sequencing of the rbcL biomarker aided in identification of the isolate as T. obliquus. Tetradesmus obliquus UJEA_AD was further batch-cultivated autotrophically in BG11 medium and examined for biomass accumulation, CO 2 biofixation rate, biochemical composition and fatty acid production. The results showed a maximum biomass accumulation of 2.78 ± 0.019 g L −1 with biomass productivity of 0.153 ± 0.001 g L −1 day −1 and specific growth rate of 0.13 ± 0.004 day -1 as well as CO 2 biofixation rate of 0.265 ± 0.002 gCO 2 L −1 day −1 . The biochemical data of the isolate revealed 27.17% ± 0.021% carbohydrate, 38.00% ± 0.15% protein and 31.2% ± 0.80% lipids; with primary fatty acids such as palmitic acid (34.26% ± 2.02%), linolenic acid (18.08 ± 5.29), trans-13-octadecenoic acid (12.32 ± 0.92) and phytol, 2-methylbutanoate (12.31 ± 1.02).CONCLUSION: These findings suggest that T. obliquus UJEA_AD is capable of producing bioproducts of economic value with an excellent CO 2 bio-mitigation potential when cultivated at optimum conditions in an autotrophic mode. Moreover, lipid extracted from T. obliquus UJEA_AD met the biodiesel quality standards of the USA and EU, making the isolate a promising commercial biodiesel feedstock.

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).