Wax Ester and Triacylglycerol Biosynthesis in Bacteria
Bacteria are an extremely diverse group of organisms, some of which possess the ability to synthesize and accumulate neutral lipids, such as triacylglycerols (TAG) and wax esters (WE). Among these microorganisms, Actinobacteria are specialized in the accumulation of TAG, whereas Gram-negative Proteobacteria, such as Acinetobacter and Marinobacter, produce predominantly WE. The capability for accumulating large amounts of TAG seems to be restricted to some members of Actinobacteria, such as those belonging to Rhodococcus, Gordonia, and Streptomyces genera, and to the Gram-negative Alcanivorax borkumensis. The biosynthesis and accumulation of TAG and/or WE require the occurrence of a set of genes/proteins working in a coordinated metabolic and regulatory context in the cell. Some components of the lipid-accumulating machinery in native producers have been identified and characterized. They include genes coding for: (1) enzymes catalyzing the last reactions of TAG and/or WE synthesis; (2) enzymes involved in the reduction of fatty acids to the respective fatty alcohols for the synthesis of WE; (3) enzymes of central metabolism which generate NADPH for fatty acid synthesis; (4) a structural protein involved in the assembly and stabilization of lipid inclusion bodies; and (5) a lipid transporter protein involved in the balance and homeostasis of cellular lipids. Some of these genes identified in native producers have been used for engineering bacterial hosts, which are naturally unable to produce these lipids, in order to produce TAG/WE with bacterial strains of biotechnological relevance.
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