Microbial Community Structures Differentiated in a Single- Chamber Air-Cathode Microbial Fuel Cell Fueled with Rice Straw Hydrolysate

Abstract

Background: The development of advanced biofuels from lignocellulosic biomass will require the use of both efficient pretreatment methods and new biomass-deconstructing enzyme cocktails to generate sugars from lignocellulosic substrates. Certain ionic liquids (ILs) have emerged as a promising class of compounds for biomass pretreatment and have been demonstrated to reduce the recalcitrance of biomass for enzymatic hydrolysis. However, current commercial cellulase cocktails are strongly inhibited by most of the ILs that are effective biomass pretreatment solvents. Fortunately, recent research has shown that IL-tolerant cocktails can be formulated and are functional on lignocellulosic biomass. This study sought to expand the list of known IL-tolerant cellulases to further enable IL-tolerant cocktail development by developing a combined in vitro/in vivo screening pipeline for metagenome-derived genes. Results: Thirty-seven predicted cellulases derived from a thermophilic switchgrass-adapted microbial community were screened in this study. Eighteen of the twenty-one enzymes that expressed well in E. coli were active in the presence of the IL 1-ethyl-3-methylimidazolium acetate ([C 2 mim][OAc]) concentrations of at least 10% (v/v), with several retaining activity in the presence of 40% (v/v), which is currently the highest reported tolerance to [C 2 mim][OAc] for any cellulase. In addition, the optimum temperatures of the enzymes ranged from 45 to 95°C and the pH optimum ranged from 5.5 to 7.5, indicating these enzymes can be used to construct cellulase cocktails that function under a broad range of temperature, pH and IL concentrations.

Screening of glycoside hydrolases and ionic liquids for fibre modification

“…For endoglucanases, GH families 5, 7, 12, and 45, and for xylanases, GH families 10 and 11 were represented (Table ). Enzymes of bacterial and fungal origin were involved and special attention was paid to involve enzymes with notable thermostability due to the previously suggested correlation between thermostability and IL tolerance . A miniaturized screening assay was developed to allow high throughput operation and to minimize the use of ILs and enzymes in the screening.…”

Biocatalysts for biomass deconstruction from environmental genomics

“…While most detected proteins were homologous to existing CAZy families, several contained unknown catalytic domains linked to CBMs for cellulose and xylan. In another study, Gladden and colleagues identified thermotolerant and ionic-liquid tolerant cellulases from a microbial community enriched on switchgrass using a combination of metagenomics and expression screening [22 ]. Candidates identified in silico were synthesized and expressed in vitro using an Escherichia coli cell free system and in vivo using a low copy plasmid.…”

Characterization of agave bagasse as a function of ionic liquid pretreatment

“…The FE-SEM images of untreated and IL pretreated AGB were taken at 5,000x and 10,000x magnification ( ; therefore a watching step is necessary to remove residual IL from biomass prior to addition of enzymes [39]. Developing IL-tolerant enzymes and microorganisms to conduct enzyme hydrolysis and microbial fermentation in one bioreactor, or using aqueous IL solutions (20e50% IL) to pretreat biomass and potentially reduce the amount of washing required prior to enzymatic saccharification are some of the current options to make the IL pretreatment more efficient [40].…”