Effects of Stress conditions on Lipid Production By Botryococcus braunii, Tetraselmis suecica, and Coccomyxa

The effects of stress conditions on neutral lipid accumulation by the microalgae Botryococcus braunii, Tetraselmis suecica and Coccomyxa were investigated to assess their suitability for biodiesel production. The growth media (3N-BBM+V for B. braunii, and Coccomyxa and F/2 for T. suecica) were altered to impose salt stress (0.1 and 0.2 M NaCl for BBM medium) and up to 1.2 M NaCl for F/2 medium. Tetraselmis suecica and Coccomyxa were also cultivated under nitrogen depletion conditions (50%, 25% nitrogen and nitrogen free) to monitor growth and investigate neutral lipid accumulation.
It was found that B. braunii grew very slowly despite using the relatively nutrient rich BBM medium. It was difficult to reach sufficient biomass to run experiments for B. braunii, but faster growth was achieved using a 2 litre fermenter. B. braunii had a total lipid content of 29% but only 3.64% were neutral (storage) lipids. This is much less than the 30% neutral lipid normally quoted as the minimum requirement for biodiesel production (Chisti, 2007). The B. braunii strain (CCAP 807/1) used failed to grow in the presence of 0.1 or 0.2 M NaCl.
Tetraselmis suecica grew in the higher salinity media, but salt stress did not induce higher lipid accumulation. Nitrogen free medium did induce more neutral lipid accumulation in T. suecica even though the growth rate and final biomass level reached were decreased. Tetraselmis suecica had less than the 30% neutral lipid normally quoted as the minimum requirement for biodiesel production, but it is an excellent candidate for production of biodiesel based on the fatty acids produced which are principally C16:0 and C18:1.
Neutral lipid accumulation increased rapidly with increasing nitrogen starvation from 25% nitrogen to nitrogen-free medium as Coccomyxa grew to reach stationary phase over four weeks. Nitrogen free medium induced more neutral lipid accumulation (31%) in Coccomyxa, which was the highest percentage found in the current work and meets the 30% neutral lipid figure suggested by Chisti et al. (2007).