To research the potential ability of tochukaso and related species to act as biocatalysts, we screened 10 entomogenous fungal strains. The recommended medium (potato dextrose broth) and a synthetic medium (PGO medium) were tested as the liquid media for culturing these fungi. Four strains (NBRC33061, 100684, 103832, and 109003) cultured using the PGO medium showed a good growth. The stereoselective reduction of a- and b-keto esters by these four strains was also investigated, and they were found to be able to reduce various a-keto esters. Specifically, the reduction of a-keto esters by the PGO-cultivated Isaria cicadae NBRC33061 strain in the presence of L-glutamate as an additive yielded corresponding a-hydroxy esters with a high conversion ratio and in excellent enantioselectivity. Furthermore, it was found that the PGO-cultivated NBRC109003 strain in the presence of L-glutamate stereospecifically reduced ethyl 2-methyl-3-oxobutanoate to (2S, 3S)-2-methyl-3-hydroxybutanoate, i.e., only one of the four theoretically possible isomers. Overall, tochukaso and related species were shown to have a great potential for application as biocatalysts for the stereoselective reduction of carbonyl compounds.
