Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Conversion of Natural and Transgenic Sugarcane and Poplar Variants with an Ionic-Liquid-Based Feedstocks-To-Fuels Pipeline

Authors:

Md Tahmid Islam1,2* (mdislam@lbl.gov), Venkataramana Pidatala1,3, Blake Simmons1,3, John Gladden1,2, Alberto Rodriguez1,2, Jay Keasling1,3

Institutions:

1Joint BioEnergy Institute; 2Biomaterials and Biomanufacturing, Sandia National Laboratories; 3Biological Systems and Engineering, Lawrence Berkeley National Laboratory

Abstract

The four DOE Bioenergy Research Centers (BRCs) have recently launched extensive formal collaborative projects with the goal of accelerating the common science goals for the bioenergy enterprise. Each BRC has integrated process concepts and feedstocks that feature novel deconstruction technologies and conversion platforms that transform plants to biofuels and bioproducts. In particular, the Joint BioEnergy Institute has developed a Feedstocks-to-Fuels pipeline for screening the efficiency of deconstruction and microbial conversion of lignocellulosic biomass. Here researchers present results obtained from subjecting two types of bioenergy feedstocks (sugarcane and poplar) to this pipeline consisting of an ionic liquid (IL) pretreatment process, enzymatic saccharification, and microbial conversion to the jet-fuel precursor bisabolene.

In this study researchers explore the conversion potential of two engineered sugarcane varieties named oilcane, 1565 and 1566 that produce high levels of lipids and the CP88 wild type (WT), developed at the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI). The starting material for the conversion experiments was the bagasse obtained after pressing, drying, and milling the biomass. Researchers also evaluated the use of natural poplar variants with different wood density developed at the Center for Bioenergy Innovation (CBI). Poplar biomass with higher wood density can increase biomass yield per hectare while reducing transportation costs, but the impact of density on the degree of conversion to sugars and bioproducts remains unexplored. Pretreatment was performed using the ionic liquids cholinium lysinate and ethanolamine acetate at different concentrations (10 to 85 wt.%), with 15 wt.% solid loading in high-pressure and high-temperature glass tube reactors at 140 °C for 3 hours. The pretreated feedstocks underwent enzymatic hydrolysis using a cellulase: hemicellulase enzyme cocktail (9:1 vol/vol, 30 mg/g biomass) and incubated at 50 °C for 72 hours. Compositional analysis of the raw and pretreated samples was performed using a 2-step acid hydrolysis method and high-performance liquid chromatography was used to quantify the sugars released during this reaction and after enzymatic hydrolysis. The WT sugarcane contained 37% glucan, while engineered sugarcane contained 39%, with lignin content below 24% for both WT and engineered sugarcane. Pretreatment reduced lignin by 1.5-fold, increasing glucan by 1.3-fold. Ethanolamine acetate performed better than cholinium lysinate with engineered sugarcane, yielding 88% glucose and 57% xylose, while both solvents achieved over 94% glucose and 70% xylose yield for WT. Fermentation with Rhodosporidium toruloides showed near-complete glucose consumption and bisabolene production, underlining the effectiveness of the pipeline for conversion of different bioenergy feedstocks to bioproducts.