Aspergillus oryzae nrtA affects kojic acid production

Abstract

We analyzed the role of the nitrate transporter-encoding gene (nrtA) of Aspergillus oryzae by gene disruption. Southern hybridization analysis indicated that homologous recombination occurred at the resident nrtA locus. Real-time PCR showed that the nrtA gene was strongly inducible by NaNO₃. The nrtA disruptant did not exhibit normal growth when nitrate was available as the sole nitrogen source. These results indicate that NrtA is essential for nitrate uptake in A. oryzae. Kojic acid (KA) production was inhibited by the addition of a small amount of sodium nitrate. The nrtA-disrupted strain was deficient in the uptake of nitrate. As a result, KA production in this strain was not considerably affected by the presence of nitrate.

Graphical abstract

The expression levels of the KA biosynthesis genes (kojA, kojR, and kojT) increased markedly in the nrtA-disrupted strain in the presence of nitrate.

Key words:

• Aspergillus oryzae
• nrtA
• nitrate
• kojic acid

Acknowledgements

We thank Harue Kitagawa and Sanae Tsuji for their technical assistance.