II. B.1. Physiology, Biochemistry, and Molecular Biology of Lipid

Production: Work by SERI Subcontractors

II. B.1 .a. Introduction

Eukaryotic algae, like all photosynthetic organisms, efficiently convert solar energy into biomass. The algal research program at SERI was designed as a long-term basic research effort to adapt or use photosynthesis and related metabolic pathways to produce renewable fuels and chemicals. Research at SERI under the Aquatic Species Program (Biodiesel) has focused on ways to increase the yield of oil from microalgae for cost-effective liquid fuel production. Initially, a large component of the research performed both by subcontractors and by SERI researchers was the collection of microalgal strains from saline environments in the desert southwest of the United States (a region targeted as a feasible location for large-scale microalgal culture), marine environments, and established culture collections. These organisms were then screened and numerous species were identified as candidates for biodiesel production; this research was described in Sections II. A. and II. B. of this report. However, no one species was identified that displayed the ideal combination of rapid growth, environmental tolerance, and high lipid production. Subsequent research efforts were directed toward understanding the biochemistry and physiology of lipid production in oleaginous microalgal strains, with the idea of using strain improvement technologies (breeding, cell fusion, genetic engineering, mutagenesis and selection) to develop algal strains with optimized traits for biodiesel production.

Early in the research program it became obvious the maximal lipid accumulation in the algae usually occurred in cells that were undergoing physiological stresses, such as nutrient deprivation or other conditions that inhibited cell division. Unfortunately, these conditions are the opposite of those that promote maximum biomass production. Thus, the conditions required for inexpensive biodiesel production, high productivity and high lipid content, appeared to be mutually exclusive. To overcome this problem, research efforts were focused on understanding the biochemistry and physiology of lipid accumulation, with emphasis on understanding the “lipid trigger”, a mechanism that could induce production of large quantities of lipid under nutrient deprivation. In addition, research was directed toward understanding genetic variation within microalgal populations and to develop methods to screen for high-lipid subpopulations within algal cultures. The knowledge of the biochemistry and physiology of lipid synthesis, combined with basic studies on microalgal molecular biology, was used in the later years of the project in attempts to use genetic engineering to develop microalgal strains with optimal properties of growth and lipid production.

Part II. B.2. of this report describes work by ASP subcontractors to understand the biochemistry and physiology of lipid accumulation in microalgae, including ultrastructural studies, the development of methods for screening for high lipid strains, and attempts to understand the biochemical lipid trigger. The research performed by SERI/NREL subcontractors on the physiology, biochemistry, and molecular biology of lipid production in oleaginous microalgae

took place during the second half of the 1980s and is presented here, roughly chronologically, according to the work performed by the individual subcontractors.