Efficacy of ionic liquids on the growth and simultaneous xylanase production by Sporotrichum thermophile: membrane integrity, composition and morphological investigation

Abstract

Ionic liquids (ILs) are emerging as promising solvent systems for carrying out various biochemical reactions. The application of whole microbial cells for carrying out catalysis in the presence of ILs is gaining interest due to the advantages of being cost effective and providing a natural environment for enzymes. Present study elucidates the tolerance of a thermophilic fungus, S. thermophile, towards various hydrophilic imidazolium based ILs. [EMIM][OAc], [BMIM][MeSO₄] and [BMIM][Otf] were found to be compatible and did not affect the growth and xylanase production whereas [HMIM][BF₄] and [BMIM][BF₄] were not compatible and inhibited the growth drastically. The impact of two types of the ILs systems, compatible [EMIM][OAc] and non-compatible [BMIM][BF₄], on S. thermophile membrane permeability, surface morphology, membrane characteristics and fatty acid composition were studied by SEM, TEM, AFM and FAME analysis. [EMIM][OAc] was tolerated by S. thermophile upto 4.0% (v/v) concentrations and the cellular response in this particular IL was comparable with that of a control. In order to explore the feasibility of using whole cells of S. thermophile in place of its crude xylanase, a study was conducted for in situ pre-treatment and saccharification of [EMIM][OAc] treated wheat straw and a high amount of reducing sugars were released as compared to controls. IL stable cells can thus be utilised for simultaneous pre-treatment and saccharification.