Relationship between Interfacial Hydrophobicity and Hydroxylation Activity of Fungal Cells Located on an Organic–Aqueous Interface

Abstract

A Liquid–liquid interface bioreactor (L–L IBR), which consists of a hydrophobic organic solvent (an upper phase), a layer of fungal cellballooned polyacrylonitrile microsphere (diameter, 20-40 μm; density, 0.03-0.20; a middle phase), and a liquid medium (a lower phase), is a unique and effective cultivation system for the microbial transformation with fungi [1]. The system has some interesting and practically important characteristics, i.e., alleviation of toxicity of poisonous substrate and/or product solubilized in the organic phase, excellent productivity of valuable hydrophobic chemicals, efficient supply of oxygen from the organic phase to fungal cells, control and management of pH and nutrients in the liquid medium, depression of catabolize repression caused by easily metabolizable carbon sources [2], and easy recovery of product without troublesome solvent extraction. The system has been applied to various microbial reactions, such as hydrolysis of an acetate ester [1,3], asymmetric reduction of an aromatic dike tone [4], and regio- and stereo selective epoxidation of - caryophyllene to (–)-β-caryophyllene oxide so far [5]. In all cases, it has been observed that substrate concentration, product accumulation, and region- and stereo selectivity’s of reaction reached very high level compared with two traditional cultivation systems, submerged and organic–aqueous two-liquid-phase systems.