I.A.1.h. Detailed Analyses of Microalgal Lipids

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National Renewable Energy Laboratory

The results indicated that the N content and conductivity of the medium were the most important

variables affecting lipid content (Nile Red fluorescence) of both NAVIC1 and CHAET9. As N

levels and conductivity increased, the amount of neutral lipid per mg of AFDW decreased. The

interaction of N and conductivity was an important determinant of lipid content as well. Silicon

level and alkalinity were more important factors in determining the lipid content for CHAET9

than for NAVIC1. Nitrogen concentration was by far the most important factor in determining

final cell mass for NAVIC1, and was a major factor for cell mass yield in CHAET9 (along with

the interaction of conductivity and alkalinity, which had a large negative impact on growth).

Alkalinity was a major factor for growth of both NAVIC1 and CHAET9. However, these

experiments did not determine actual growth rates, but only the final cell yields; thus, how actual

cell division rates compared with each other is not known.

These experiments indicate the importance of examining the interactions of environmental

variables in determining the effects on growth and lipid production. However, the models

generated by these kinds of experiments are specific for the strains being studied, and the results

cannot necessarily be used to predict the effects of these variables on other strains. Furthermore,

for such models to be truly predictive of growth and lipid production in an actual mass culture,

much more sophisticated (and realistic) experimental setups would be required.

Publications:

Chelf, P. (1990) AEnvironmental control of lipid and biomass production in two diatom species.@

J. Appl. Phycol. 2:121-129.

II.A.1.h. Detailed Analyses of Microalgal Lipids

In addition to the in-house research being conducted in the area of strain collection and screening,

there was an effort by Dr. Thomas Tornabene and others to characterize various strains via

detailed lipid compositional analyses. Dr. Tornabene=s laboratory at SERI (and later at the

Georgia Institute of Technology) served as the focal point for the analysis of lipids in algal

samples supplied by researchers in the ASP. This section will describe the results of these

analyses, and will provide details about the analytical methods used, as these methods were the

most comprehensive used in the program. An early report by Tornabene et al. (1980) described

the lipids present in the halophilic alga Dunaliella that had been isolated from the Great Salt Lake

in Utah. The cells were grown to late logarithmic phase, harvested, and extracted with

chloroform/methanol via the method of Bligh and Dyer (1959). Additional extraction by acetate

buffer, followed by refluxing with an alkaline methanol/water mixture was then performed,

followed by partitioning of lipids into petroleum ether. The extracted lipids were fractionated on

the basis of polarity using silicic acid columns via differential elution with hexane, benzene,

chloroform, acetone, and methanol. In this procedure, the lipids are eluted as follows:

hexane: acyclic hydrocarbons

benzene: cyclic hydrocarbons, polyunsaturated acyclic hydrocarbons, sterols,

and xanthophylls

A Look Back at the Aquatic Species Program--Technical Review