Introduction (cont)

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National Renewable Energy Laboratory

microalgal species can be induced to accumulate substantial quantities of lipids, often greater than

60% of their biomass. Microalgae can also grow in saline waters that are not suitable for

agricultural irrigation or consumption by humans or animals. The growth requirements are very

simple, primarily carbon dioxide (CO2) and water, although the growth rates can be accelerated

by sufficient aeration and the addition of nutrients. A brief overview of the characteristics of the

major microalgal classes can be found in Section II.A.2. of this report.

A major undertaking by ASP researchers in the early stages of the program was to identify

candidate microalgal species that exhibited characteristics desirable for a commercial production

strain. Resource analyses carried out by SERI (discussed in Section III.C.) indicated that the

desert regions of the southwestern United States were attractive areas in which to locate

microalgal-based biodiesel production facilities. This, in part, dictated the required strain

characteristics. These characteristics included the ability of the strains to grow rapidly and have

high lipid productivity when growing under high light intensity, high temperature, and in saline

waters indigenous to the area in which the commercial production facility is located. In addition,

because it is not possible to control the weather in the area of the ponds, the best strains should

have good productivity under fluctuating light intensity, temperature, and salinity.

A multi-faceted effort was carried out to:

isolate microalgae from a variety of saline habitats (including oceans, lakes,

ponds, and various ephemeral water bodies),

screen those isolates for the ability to grow under a variety of conditions,

analyze the biochemical components of the strains (especially with respect

to lipids), and

determine the effects of environmental variables on the growth and lipid

composition of selected strains.

This effort involved in-house researchers and subcontractors from academia, industry, and other

government laboratories. Section II.A.1 documents the efforts of SERI in-house researchers in

the area of microalgal strain isolation and screening. It also describes the methodologies

developed and employed during the isolation, screening, and characterization phases of the work.

Section II.A.2 describes parallel efforts conducted by SERI subcontractors. An account of the

history and current status of the NREL Microalgae Culture Collection is presented in Section

II.A.3.

Although the collection and screening efforts produced a number of viable candidate strains, no

one algal strain was identified that exhibited the optimal properties of rapid growth and high

constitutive lipid production. Many microalgae can be induced to accumulate lipids under

conditions of nutrient deprivation. If this process could be understood, it might be possible to

manipulate either the culture conditions, or to manipulate the organisms themselves, to increase

lipid accumulation in a particular strain. Therefore, studies were initiated both at SERI and by

ASP subcontractors to study the biochemistry and physiology of lipid production in oleaginous

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