Improvement of the potential of Dunaliella tertiolecta as a source of biodiesel by auxin treatment coupled to salt stress

Increased world demand for energy and decrease of petroleum reserves have focused worldwide efforts to develop new and renewable energy sources. Liquid microalgal biofuels such as biodiesel represent a sustainable alternative to fossil energy besides being environmentally friendly. However, optimization of culture conditions to maximize productivity (biomass and lipid) is still a great challenge for a commercial biodiesel production. This is due to the difference between optimal culture conditions required for biomass and lipid accumulation. The current study proposes a two-phase method allowing both biomass and lipid increase in Dunaliella tertiolecta. The used this method consists of a first phase when microalgae were cultivated in presence of 2,4-Dichlorophenoxyacetic acid (2,4-D) to enhance algal division and growth. Later, at the end of log-phase, culture conditions were modified by adding NaCl to suddenly increase the salinity from 0.5 M to 2 M. Results showed that combination of auxin with salt stress resulted in a considerable improvement both in growth and lipid production in D. tertiolecta. During the first phase auxin addition improved biomass accumulation by 40% and salt stress in the second phase led to lipid increase from 24% to 70% with the optimal concentrations combination of auxin and NaCl.