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Studies [1] have shown that lactase is produced by A. oryzae when grown on wheat bran and spent beer grains.

  1. Why would A. oryzae produce lactase when these substrates have no lactose?
  2. In [1], it's shown that A. oryzae produces more lactase when grown on wheat bran vs when grown on whey, which has lactose in it - what might explain that?
  3. Since lactose is found in mammals and is not common elsewhere, how/why could A. oryzae have evolved the ability to produce lactase in the first place?

[1] Bailey, M. J., & Linko, M. (1990). Production of β-galactosidase by Aspergillus oryzae in submerged bioreactor cultivation. Journal of Biotechnology, 16(1-2), 57–66. doi:10.1016/0168-1656(90)90065-j

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"Although beta-galactosidase is mainly produced for utilization in the hydrolysis of lactose in milk or whey, in natural systems this enzyme is also involved in the breakdown of galactan-based hemicelluloses. Wheat bran contains almost 30% hemicellulose, including considerable amounts of galactose residues (Salo and Kotilainen, 1970). Similar residues are presumably also present in spent grain (wheat). "

From the paper linked in the question.

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