(694c) Whole-Cell Bioconversion of Phytosterols in Ionic Liquids Co-Solvents with Alleviation of Product Inhibition

Androst-4-ene-3,17-dione (AD) obtained by sterols side-chain cleavage is a vital intermediate of steroids. However, product (AD) inhibition and low substrate (sterols) water-solubility limit the further improvement of the bioconversion efficiency. For these two reasons, ionic liquids (ILs) capable of dissolving many insoluble substrates and poly (2-hydroxyethyl methacrylate) (pHEMA) cryogel microbeads with ability to adsorb AD were used in this work for sustainable bioconversion of phytosterols to produce AD.

First, cholinium amino acids ([Ch][AA]) ILs with good biocompatibility were introduced as co-solvents in phytosterols bioconversion by Mycobacterium sp. MB 3683 resting cells. The physicochemical properties (density, viscosity, hydrophobicity and polarity) of [Ch][AA] ILs were investigated based on their chemical structures. The solubility of phytosterols and AD in [Ch][AA] ILs aqueous solution was measured. The results indicated that [Ch][AA] ILs especially [Ch][Glu], [Ch][Asp] and [Ch][Gln] showed proper biocompatibility to Mycobacterium sp. MB 3683 cells and the production of AD in 1% [Ch][Asp] was about twice as that in the buffer. Moreover, pHEMA cryogel microbeads with pore size of 1~50 μm were added to the fermentation process of phytosterols by Mycobacterium sp. MB 3683. Obviously, pHEMA cryogel microbeads were found to promote the bioconversion to produce AD due to their high capacity of adsorption to AD. The effects of dry cell weights, phytosterols concentration on AD production, and the synergy interaction of pHEMA cryogel microbeads and preferred ILs were investigated in detail.

In situ removal of AD by pHEMA cryogel microbeads reduced the toxicity of products to cells and thus the production of AD was increased, as well as the subsequent separation process was simplified. Thus, by the addition of [Ch][AA] ILs and pHEMA cryogel microbeads respectively, two problems that limit AD production have been effectively solved, which is potential for microbial side-chain cleavage of phytosterols and up-scale AD production.

Keywords: Cholinium amino acids ionic liquids; pHEMA cryogel microbeads; Bioconversion; Phytosterols