misinterpretation because of the species-specific staining differences described earlier. Nonetheless, before Nile Red was used, quantitating lipids from cells was very time consuming. It required the extraction of lipid from a large number of cells using organic solvents, evaporation of the solvent, and determination of the amount of lipid by weighing the dried extract. Consequently, the use of Nile Red as a rapid screening procedure can still have substantial value.
The estimation of lipid content using a simple procedure such as the Nile Red assay is clearly an important component of a rapid screening procedure for identifying promising strains, but an equally important component is a means to identify strains that grow rapidly under the expected culture conditions. Reports detailing the amount and types of saline groundwater available in the southwestern United States, along with data concerning the high rates of evaporation in this region, indicated that tolerance of algal strains to high conductivity (higher than 50 mmho- cm ) could be important. Therefore, an additional component of the secondary screening procedure developed to reduce the number of strains being maintained by ASP
researchers. Algae were tested for the ability to grow at high conductivity (55 mmho
• cm , both Type I and Type II media), high temperature (30° C), and high light
intensity (average of 200 ^E- m • s , 12 h light: 12 h dark cycle) in cultures that were continually agitated via aeration. To prevent osmotic shock, strains were adapted to higher conductivities via a stepwise transfer into media with increasing conductivity at 2-day intervals. Tubes were used that could be placed directly in a
This newly developed rapid screening protocol was subsequently used both in Milt spectrophotometer (i.e., 25 mm diameter, 50 mL volume), allowing the culture
Sommerfeld's laboratory and at SERI .to screen many, microalgal isolates. Keith density to be measured without removing a sample. The tubes also held enough
Cooksey's laboratory also examined numerous strains using this procedure. medium to allow samples to be taken for Nile Red lipid analysis (both for N-sufficient
Sommerfeld's laboratory examined approximately 800 strains that had been collected and N-deficient cells), and for ash-free dry mass determinations. The tubes were over the previous 2 -Years of the subcontract. Only 102 of these strains survived placed in a rack and illuminated by fluorescent lamps from below for the screening prosfdu rinto OpeKte measurementy \(\fere$taleThcwi(Ciltia iO ffoh es e(aYsa(CTSrir40
ppwniinbothi foypth i/5deaeririrnip g rowh na<ed^a , 4¡2lgFe5s wey ire lI:oi?tdI/f05 eaedfUlC , auoroHgrfiiwi inl^íysfsT;(Cu<rií^|/5ekppTci¿TTlíill gpow10 iBrsflesttf:tefc\£i n|aySf^(fTrfsizolrc3T|S\\aitt]]f
U]TfffeFSfife)rpfd4IIdacYSf,(;alRIShofwef dnfTafencyI • A.2.
Table II.A.2 Fastest growing strains from Arizona State University collection.
V.A. SERI/NREL/DOE REPORTS AND PUBLICATIONS V.B. ADDITIONAL REFERENCES V.C. PATENTS
Was this article helpful?