Effect of quaternary ammonium ionic liquids on fermentation of cellulose by bacteria

Abstract

Biofuel and chemical production from lignocellulosic biomass gained significant attention due to high demand of fuels and chemicals. The polysaccharides in lignocellulosic biomass are converted to monosaccharides through enzymatic hydrolysis. The monosaccharides are converted to bioethanol and bio-based chemicals via fermentation. However, the recalcitrance of lignocellulosic biomass to hydrolysis demands a pretreatment process. Current pretreatment methods either have high energy demand or produce wastestreams that are harmful to the environment. Recently, ionic liquids (ILs), which are salts in liquid state, are introduced and utilized as green solvents for cellulose dissolution. However, recent studies showed that ILs are not as “green” as they thought to be in the past. ILs are not only inhibitory to biological processes following the pretreatment, but also they cause ecotoxicity and proliferate antimicrobial resistance among bacteria when released into the environment. The main objective of this research is to couple pretreatment, hydrolysis and fermentation for production of value-added alcohols and organic acids from cellulose in a single phase; utilizing benzalkonium chlorides (BACs), an extensively used quaternary ammonium IL as the reaction medium, cellulose degrading microbial community developed from soil and BACs resistant/degrading Pseudomonas sp. BIOMIG1 as biocatalysts. A microbial community capable of cellulose degradation was developed and the cellulose degradation was tested both in absence and presence of BACs. The soil microbial community utilized 1000 mg/L cellulose aerobically within 6 days. Cellulose utilization by the microbial community was inhibited at and above 50 mg BAC/L. On the other hand, when Pseudomonas sp. BIOMIG1 was supplemented to the community, BACs was utilized at up to 500 mg BAC/L. In addition, the co-culture of BACs resistant Pseudomonas sp. BIOMIG1 and Serratia marcescens BIOMIG4 converted glucose mainly to 2,3 butanediol, ethanol and various acids. In conclusion, a biological system that can convert cellulose to value added organic chemicals in the presence of a quaternary ammonium IL and alleviate the environmental consequences of IL was developed in this study.