Metabolic engineering of Aureobasidium melanogenum for the overproduction of putrescine by improved L-ornithine biosynthesis

Aureobasidium melanogenum HN6.2 is a high siderophore-producing yeast-like fungal strain. After blocking siderophore biosynthesis and attenuating the expression of the ornithine carbamoyltransferase gene (the OTC gene), the obtained D-LCFAO-cre strain produced 2.1 +/- 0.02 mg of intracellular L-ornithine per mg of the protein. The overexpression of the L-ornithine decarboxylase gene (the SPE1-S gene) from Saccharomyces cerevisiae in the mutant D-LCFAO-cre could make the transformant E-SPE1-S synthesize 3.6 +/- 0.1 of intracellular ornithine per mg of protein and produce 10.5 g/L of putrescine. The further overexpression of the ArgB/C gene encoding bifunctional acetylglutamate kinase/N-acetyl-gamma-glutamyl-phosphate reductase in the transformant E-SPE1-S caused the transformant E-SPE1-S-ArgB/C to accumulate L-ornithine (4.2 mg/mg protein) and to produce 21.3 g/L of putrescine. During fed-batch fermentation, the transformant E-SPE1-S-ArgB/C could produce 33.4 g/L of putrescine, the yield was 0.96 g/g of glucose, and the productivity was 0.28 g/L/h. The putrescine titer was much higher than that produced by most engineered strains obtained thus far.

Automated summary

In this study, the strain Aureobasidium melanogenum HN6.2 was genetically engineered to enhance siderophore production, ornithine synthesis, and putrescine production. The overexpression of specific genes successfully increased the yields of ornithine and putrescine, making this strain a promising candidate for industrial applications.