Overexpression of kojR and the entire koj gene cluster affect the kojic acid synthesis in Aspergillus oryzae 3.042.

Kojic acid (KA), a fungal secondary metabolite, has various applications in the cosmetics, pharmaceutical, and food industries. Aspergillus oryzae, the primary strain, has been identified as a koj gene cluster positively responsible for KA biosynthesis. In this study, we obtained transformants T58 and T31, which overexpressed either solo kojR or the entire koj gene cluster, respectively. These transformants exhibited peak KA production on the 5th day of shake flask fermentation, with 32.5 g/L and 26.57 g/L that 324.28 % and 246.87 % higher than the control strain with 7.64 g/L, respectively. Morphological analysis revealed that the highly productive KA strains had reduced conidial production but increased antioxidant capacity. The qRT-PCR analysis revealed that relative expression levels of kojR in the transformants were remarkably higher that the primary cause for the increased KA yield. Moreover, the high expression of kojR could also influence the expression of the key enzymes involved in the KA biosynthesis process, such as glucose dehydrogenase and gluconate dehydrogenase. These findings can assist in discovering more about how the koj gene cluster in A. oryzae influences its growth and KA production. And provides valuable insights into facilitating strain improvement and benefits for the future.