Production: NREL In-House Researchers

II. B.2.a. Introduction

During the first few years of the ASP, in-house research efforts in the area of lipid biosynthesis focused on understanding the lipid trigger and the effects of N starvation on lipid synthesis and photosynthetic efficiency. It was also shown that lipid accumulation can be induced in diatoms by Si starvation, a major component of the diatom cell wall. During the second half of the 1980s

and early 1990s, a major component of the research at SERI/NREL was the study of lipid biosynthesis in the oleaginous diatom C. cryptica. This was primarily the work of Paul Roessler, who identified a key enzyme involved in lipid accumulation and isolated and characterized both the protein and the gene for the enzyme acetyl-CoA carboxylase from Cyclotella. Other research efforts at NREL examined related biosynthetic pathways, including synthesis of chrysolaminarin, a storage carbohydrate, and lipid processing reactions such as fatty acid desaturation. The basic biochemistry and molecular biology research formed the basis of the efforts to manipulate microalgal lipids by genetic engineering, which will be described in Section II. B.3.

One aspect of the algal research at SERI was the possibility of producing hydrogen by microalgae, for use as a gaseous fuel. During photosynthetic electron transport, electrons from reduced ferredoxin can be transferred to hydrogen ions to produce H2. This reaction is catalyzed by the enzyme hydrogenase. Unfortunately, hydrogenase is inhibited by molecular oxygen, a by­product of the photosynthetic reaction, making the practical application of this process difficult. There was a significant research effort at SERI in the early 1980s, primarily by Dr. Steve Lien and Dr. Paul Roessler, to understand the biochemistry of hydrogen production by microalgae. The work on hydrogenase was funded by the Hydrogen Program at DOE, not the ASP, and will not be included in this report. However, studies on hydrogen production by microalgae are ongoing at NREL (SERI) in the Center for Basic Sciences, and interested readers should contact Dr. Michael Seibert for more information.