ObjectiveA novel biocatalyst for Baeyer-Villiger oxidations is necessary for pharmaceutical and chemical industries, so this study aims to find a Baeyer-Villiger monooxygenase (BVMO) and to improve its stability by immobilization. ResultsAcetone, the simplest ketone, was selected as the only carbon source for the screening of microorganisms with a BVMO. A eukaryote, Fusarium sp. NBRC 109816, with a BVMO (FBVMO), was isolated from a soil sample. FBVMO was overexpressed in E. coli and successfully immobilized by the organic-inorganic nanocrystal formation method. The immobilization improved the thermostability of FBVMO. Substrate specificity investigation revealed that both free and immobilized FBVMO were found to show catalytic activities not only for Baeyer-Villiger oxidation of ketones to esters but also for oxidation of sulfides to sulfoxides. Furthermore, a preparative scale reaction using immobilized FBVMO was successfully conducted. ConclusionsFBVMO was discovered from an environmental sample, overexpressed in E. coli, and immobilized by the organic-inorganic nanocrystal formation method. The immobilization successfully improved its thermostability.