Isolation and characterization of microalgae for biodiesel production from seawater

• Salinity exhibited significant positive impact on biomass and lipid production.
• As a light dependent strain, autotrophic cultivation was the optimally trophic type.
• N. gaditana Q6 was more sensitive to the variance of NH4HCO3 than NaH2PO4.

As green marine microalgae isolated from local seawater in Tianjin, China, Nannochloropsis gaditana Q6 was tolerant to the variation of salinity with the highest biomass and lipid concentration in natural seawater medium. Although this strain could grow mixotrophically with glycerol, the narrow gap between mixotrophic and autotrophic cultivation suggested that autotrophic cultivation was the optimal trophic type for N. gaditana Q6 growth. In addition, strain Q6 was more sensitive to the variance of NH4HCO3 concentration than NaH2PO4 concentration. Consequently, the lipid production could be maximized by the two-stage cultivation strategy, with an initial high NH4HCO3 concentration for biomass production followed by low NH4HCO3 concentration for lipid accumulation.