Verticillium sp. GF39, catalyzing the oxidation of 1-methylisoquinoline to 1-methylisoquinoline N-oxide, was found to be the highest N-oxide producer. Under the optimized reaction conditions, the whole cells of Verticillium sp. GF39 formed 5 mM 1-methylisoquinoline N-oxide from 1-methylisoquinoline with a molar conversion yield of 100% after a 10-h incubation at 20 degrees C. The whole cells also acted on pyridine, 2-methylpyridine, quinoline and isoquinoline and formed the corresponding N-oxides. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.