Mixotrophic and carbon fixation culture of nervonic acid-producing microalgae Mychonastes afer

Microalgae are a group of single cell microorganism, which play an important role in aquatic production such as aquatic feeding and water regulating. This research focuses on the growth and photosynthetic capacity of Mychonastes afer and Chlorella sorokiniana under different nutrition and aeration conditions. The microalgae were cultivated under autotrophic, mixotrophic or heterotrophic conditions, respectively. And the influence of CO₂ concentration was also investigated. The growth curve, photosynthetic electron transfer rate, organic carbon source utilization, photosynthetic oxygen evolution and respiratory oxygen consumption rate were measured to inflect the differences between M. afer and C. sorokiniana, and the emphasis was given to lipid components of M. afer. The results show that C. sorokiniana could grow under heterotrophic condition without light, while M. afer could not. The photosynthetic system of the two species were both inhibited by organic carbon sources, displaying lower efficiency of photosynthetic electron transfer rates and slower photosynthetic oxygen evolution rates. Besides, it is found that under mixotrophy condition, high concentration of CO₂ was beneficial to the growth of M. afer, which promoted cell utilization of glucose, and increased the production of lipid and nervonic acid. The study explores a mixotrophic condition for M. afer to produce natural nervonic acid, shows significant differences between the two algae species in photosynthetic system, and explores the cooperative utilization of external organic carbon sources.