Understanding wax ester synthesis in Euglena gracilis: Insights into mitochondrial anaerobic respiration

Euglena gracilis, photosynthetic protist, has a unique ability to generate wax esters in the absence of oxygen, employing a distinctive fatty acid synthesis mechanism. Through comprehensive inhibitor assays and gene-silencing techniques, our research clearly emphasized the indispensable role of the mitochondrial anaerobic respiratory chain in this biosynthesis. We identified acyl-CoA dehydrogenase, electron transfer flavoprotein (ETF), and rhodoquinone (RQ) as central molecular components in the pathway. These findings strongly indicated a potential reversal of beta-oxidation occurring within mitochondria for fatty acid production in anaerobic conditions. Furthermore, our analysis revealed the pivotal function of nicotinamide nucleotide transhydrogenase (NNT) in efficiently managing the NADPH/NAD⁺ conversion essential for sustaining anaerobic metabolism. This review outlines our key findings and provides a comprehensive understanding of the molecular mechanisms that enable E. gracilis to produce wax ester anaerobically.