Pecularities of microorganisms for synthesis and production of designed lipids

Several bacteria synthesize lipids such as triacylglycerols and wax esters as storage compounds and deposit these hydrophobic compounds as insoluble inclusions in the cytoplasm. Some of bacteria excrete the lipids even into the medium. The key enzyme for synthesis of lipids in bacteria was identified for the first time as a wax ester synthase/diacylglycerol acyltransferase in the Gram-negative bacterium Acinetobacter baylyi [1]. Meanwhile, homologues of this promiscous acyltransferase were detected also in Rhodococcus opacus, Mycobacterium tuberculosis, Alcanivorax borkumensis and in any other lipid synthesizing bacterium. These acyltransferases have been characterized in detail at the biochemical and molecular level and are capable of synthesizing a wide range of different acyloxoesters and even acylthioesters with a widely varying carbon-chain-length of the constituents. The acyltransferase of A. baylyi and of other bacteria were heterologously expressed in a functional active form in non-lipid synthesizing bacteria and in yeast. Tailor-made lipids and of fatty acid ethyl esters (FAEEs), which were referred to as ‘Microdiesel’ [2], were produced in engineered bacteria. The potential of these acyltransferase for the production of fine chemicals and oleochemicals on the one side and of bulk chemicals like lipids for fuel production and FAEEs on the other side [3] will be illustrated and summarized. The source of the used acyltransferase, the physiological background of the acyltransferase, i. e. the bacterium in which this enzyme is active, mutants in fatty acid and/or fatty alcohol metabolism, and the carbon sources during growth are important factors that determine the composition of the synthesized lipids. Production of these lipids requires also high cell density fermentations of bacteria for being able to produce abundant amounts.

[1] Kalscheuer, R. & A. Steinbüchel (2003) A novel bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase mediates wax ester and triacylglycerol biosynthesis in Acinetobacter calcoaceticus ADP1. J. Biol. Chem. 278:8075-8082.
[2] Kalscheuer, R., T. Stölting & A. Steinbüchel (2006) Microdiesel: Escherichia coli engineered for fuel production. Microbiology (SGM) 152:2529-2536.
[3] Stöveken, T. & A. Steinbüchel (2008). Bacterial acyltransferases as an alternative for lipase-catalyzed acylation for the production of oleochemicals and fuels. Angew. Chem. Int. Ed. 47:3688-3694.