Nannochloropsis oculata CCMP 525, Dunaliella salina FACHB 435, and Chlorella sorokiniana CCTCC M209220 were compared in mixotrophic and photoautotrophic cultures in terms of growth rate, protein, and lipid content. Growth improved in glucose, and the biomass productivities of N. oculata, D. salina, and C. sorokiniana were found to be 1.4-, 2.2- and 4.2-fold that observed photoautotrophically. However, biomass and lipid production decreased at the highest glucose concentrations. Meanwhile, the content of protein and lipid were significantly augmented for mixotrophic conditions at least for some species. C. sorokiniana was found to be well suited for lipid production based on its high biomass production rate and lipid content reaching 51% during mixotrophy. Expression levels of accD (heteromeric acetyl-CoA carboxylase beta subunit), acc1 (homomeric acetyl-CoA carboxylase), rbcL (ribulose 1, 5-bisphosphate carboxylase/oxygenase large subunit) genes in C. sorokiniana were studied by real-time PCR. Increased expression levels of accD reflect the increased lipid content in stationary phase of mixotrophic growth, but expression of the acc1 gene remains low, suggesting that this gene may not be critical to lipid accumulation. Additionally, reduction of expression of the rbcL gene during mixotrophy indicated that utilization of glucose was found to reduce the role of this gene and photosynthesis.

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A novel green unicellular microalgal isolate from the freshwater of the Inner Mongolia Province of China and named as CCTCC M209220, grows between pH 6 and 11 and temperatures of 20-35°C with optimal conditions at pH 9 and 30°C. Morphological features and the phylogenetic analysis for the 18S rRNA gene reveal that the isolate is a Chlorella sorokiniana strain. A nitrogen source test reveals that this strain can grow well with nitrate and urea, but not ammonium. The strain can grow heterotrophically with glucose as the carbon source and accumulates lipid content as high as 56% (w/w) dry weight after 7 days in high glucose concentrations compared to 19% lipids achieved in 30 days of photoautotrophic culture. The relative neutral lipid content as a fraction of the total lipid is also much higher in heterotrophic culture as compared to photoautotrophic culture.