Secretion of fatty acids by photosynthetic microorganisms

Abstract

Recombinant photosynthetic microorganisms that convert inorganic carbon to secreted fatty acids are described. Methods to recover the secreted fatty acids from the culture medium without the need for cell harvesting are also described.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims benefit of provisional application 61 / 007,333 filed 11 Dec. 2007. The contents of this application are incorporated herein by reference.TECHNICAL FIELD[0002]This invention relates to photosynthetic microorganisms that convert inorganic carbon to fatty acids and secrete them into the culture medium, methods of production of fatty acids using such organisms, and uses thereof. The fatty acids may be used directly or may be further modified to alternate forms such as esters, reduced forms such as alcohols, or hydrocarbons, for applications in different industries, including fuels and chemicals.BACKGROUND ART[0003]Photosynthetic microorganisms, including eukaryotic algae and cyanobacteria, contain various lipids, including polar lipids and neutral lipids. Polar lipids (e.g., phospholipids, glycolipids, sulfolipids) are typically present in structural membranes whereas neutral lipids (e.g., triacylglycerols, wax esters) ...

AI Technical Summary

Benefits of technology

[0011]The present invention is directed to the production of recombinant photosynthetic microorganisms that are able to secrete fatty acids derived from inorganic carbon into the culture medium. Methods to remove the secreted fatty acids from the culture medium without the need for cell harvesting are also provided. It is anticipated that these improvements will lead to lower costs for producing lipid-based fuels and chemicals from photosynthetic microorganisms. In addition, this invention enables the production of fatty acids of defined chain length, thus allowing their use in the formulation of a variety of different products, including fuels and chemicals.

[0013]One embodiment of the invention relates to a culture of recombinant photosynthetic microorganisms, said organisms comprising at least one recombinant expression vector encoding at least one exogenous acyl-ACP thioesterase, wherein the at least one exogenous acyl-ACP thioesterase preferentially liberates fatty acid chains containing 6 to 20 carbons from these ACP thioesters. The fatty acids are formed from inorganic carbon as their carbon source and the culture contains substantially only inorganic carbon as a carbon source. The presence of the exogenous thioesterase will increase the secretion levels of desired fatty acids by at least 2-4 fold.

Problems solved by technology

Typically, eukaryotic microalgae are grown under nutrient-replete conditions until a certain cell density is achieved, after which the cells are subjected to growth under nutrient-deficient conditions, which often leads to the accumulation of neutral lipids.

Harvesting of the cells and extraction of the lipids are cost-intensive steps.

Further, there is no disclosure of converting inorganic carbon directly to secreted fatty acids using a photosynthetic organism grown in a culture medium containing inorganic carbon as the primary carbon source.

Images