Declining fossil fuel reserves have led to the necessity of developing alternative, sustainable fuel sources. One of the most promising possibilities is microalgae, as they are a renewable resource and have relatively high lipid productivity compared to conventional biofuel feedstock sources. A foreseeable obstacle to the advancement of this technology is the high cost of microalgae-based biodiesel production. Xin et al. (2010) sought to elucidate whether the antialgal allelochemical ethyl-2-methyl acetoacetate (EMA) could induce high lipid accumulation in microalgal cells, thus making the biodiesel production process more efficient and cost-effective. They conducted the experiment on a microalgae species known to have high lipid content, Scenedesmus sp. LX1, and measured the biomass and lipid productivity post-EMA exposure. They found that EMA could increase triacylglycerol (TAG) lipid and TAG productivity content by 79% and 40% respectively in this species, indicating EMA as a possible method of reducing the costs of microalgae biodiesel production.—Karen de Wolski
Xin, L., Hong-ying H., Jia Y., Yin-hu W., 2010. Enhancement effect of ethyl-2-methyl acetoacetate on triacylglycerols production by a freshwater microalga, Scenedesmus sp. LX1. Bioresource Technology 101, 9819-9821.
Xin et al. sought to experimentally determine whether the addition of the antialgal allelochemical EMA could induce higher TAG content per lipid and TAG productivity in the microalgae species Scenesdesmus sp. LX1. EMA, a compound isolated from the reed Phragmites communis, has been found to inhibit the growth of Chlorella pyrenoidosa and Microcystis aeruginosa, and the researchers therefore believed that, as an environmental stressor, EMA may result in higher lipid content in microalgae. They chose Scenesdesmus sp. LX1 as the experimental subject because it had been previously isolated and is known to have high lipid content. The microalgae were grown in different concentrations of EMA culture and the TAG content per lipid and TAG productivity were measured and calculated.
All microalgae cultures were grown in the same light intensity, light/dark periods, humidity, and temperature. The researchers added EMA to the growth medium in four different concentrations (0, 0.25, 0.5, 1.0, and 2.0 mg/L). Densities of the microalgae cultures were determined by measuring optical density (OD650) every 24 hours. These data were then extrapolated to a logistic model to find algal growth. Biomass and total lipid content were also measured. The experimenters then dissolved the dried lipids in isopropyl alcohol, and they estimated TAGs content by an enzymatic colorimetric method. Significant difference analyses were carried out by Independent-Samples t-tests.
Xin et al. found that none of the experimental EMA concentrations had a significant effect on microalgae growth. Through linear regression analysis, they also calculated that carrying capacity of culture was not significantly affected by different EMA concentrations. Lipid content per biomass and TAGs content per lipid were measured after 19 days of cultivation. Different EMA concentration did not induce significantly different biomasses (all about 30%). However, it was found that TAG accumulation was significantly higher (p<0.01) in microalgae grown in EMA concentrations of 0.5, 1.0, and 2.0 mg/L (34.8%, 78.3%, and 79.1% respectively). Additionally, TAG productivity was significantly greater in the microalgae samples grown in 1.0 and 2.0 mg/L EMA concentrations.
These results are promising because they indicate that microalgae productivity can be enhanced by EMA without hindering growth rate. This could potentially greatly reduce costs of microalgae biodiesel production. The researchers conclude that, while the exact chemical mechanisms need to be further studied, this experiment partially elucidates a possible method of overcoming the cost-barrier of wide-scale microalgae cultivation.