Study On The Effect Of Mixotrophy On The Growth, Biomass Composition, And Expression Of Three Lipid Synthesis Genes Of Three Typical Microalgae

Microalgae can grow extremely rapidly and are rich in oils that are a suitable feedstock for biodiesel production. Many microalgae exhibit higher growth rates under mixotrophic conditions than under photoautotrophic conditions. In the present study, three species of microalgae Nannochloropsis sp.. HQW03, Dunaliella salina HQW04 and Chlorella sorokiniana CS-01 under mixotrophic culture with glucose were compared with photoautotrophic culture in terms of growth, lipid and protein contents, The results show that with optimal concentrations of glucose for growth in the media, the biomass productivity of Nannochloropsis sp.., Dunaliella salina and Chlorella sorokiniana were found to be 1.4,2.2 and 4.2 fold of that obtained under photoautotrophic conditions; meanwhile, the contents of lipid and protein were increased (Nannochloropsis sp..:23% and 201%; Dunaliella salina:20% and 43%; Chlorella sorokiniana:86% and 215%, respectively). Upon comparison of the lipid yield, average lipid yield per day, and additional lipid yield with glucose of the three microalgae, Chlorella sorokiniana CS-01 proved to be the best organism for lipid production in many aspects, such as growth rate, lipid yield and productive rate, and glucose utilization efficiency.Furthermore, the expression level of accD, accl, rbcL genes in Chlorella sorokiniana CS-01 with various glucose concentrations were also studied by real-time PCR. The results show:heteromeric ACCase is one of key enzymes for lipid synthesis in Chlorella sorokiniana, as the expression level of accD can reflect lipid contents of algae in stationary phase of mixotrophic growth; Additionally, the acc1 gene coding homomeric ACCase remains constitutively expressed at low levels or even not expressed; The differential expression of the rbcL gene suggests that photoautotrophic and heterotrophic growth of Chlorella sorokiniana CS-01 cannot be proceed independently under mixotrophic conditions, and utilization of an organic carbon source will reduce the photosynthesis efficieny.