Pathway of Glycine Betaine Biosynthesis in Aspergillus fumigatus

The choline oxidase (CHOA ) and betaine aldehyde dehydrogenase (BADH ) genes identified inAspergillus fumigatus are present as a cluster specific for fungal genomes. Biochemical and molecular analyses of this cluster showed that it has very specific biochemical and functional features that make it unique and different from its plant and bacterial homologs.A. fumigatus ChoAp catalyzed the oxidation of choline to glycine betaine with betaine aldehyde as an intermediate and reduced molecular oxygen to hydrogen peroxide using FAD as a cofactor.A. fumigatus Badhp oxidized betaine aldehyde to glycine betaine with reduction of NAD+ to NADH. Analysis of theAfchoA Δ::HPH andAfbadA Δ::HPH single mutants and theAfchoA ΔAfbadA Δ::HPH double mutant showed thatAf ChoAp is essential for the use of choline as the sole nitrogen, carbon, or carbon and nitrogen source during the germination process.Af ChoAp andAf BadAp were localized in the cytosol of germinating conidia and mycelia but were absent from resting conidia. Characterization of the mutant phenotypes showed that glycine betaine inA. fumigatus functions exclusively as a metabolic intermediate in the catabolism of choline and not as a stress protectant. This study inA. fumigatus is the first molecular, cellular, and biochemical characterization of the glycine betaine biosynthetic pathway in the fungal kingdom.