Iron incorporation both intra- and extra-cellularly improves the yield and saccharification of switchgrass (Panicum virgatum L.) biomass

Chien-Yuan Lin,Haibing Yang,Manal Yunes,Todd Shollenberger,Stephen R Decker,Yannick J Bomble,Michael E Himmel,Xiaowen Chen,Hui Wei,Melvin P Tucker,Nicholas S Sarai,Bryon S Donohoe,Maureen C Mccann

doi:10.1186/s13068-021-01891-4

Abstract

BackgroundPretreatments are commonly used to facilitate the deconstruction of lignocellulosic biomass to its component sugars and aromatics. Previously, we showed that iron ions can be used as co-catalysts to reduce the severity of dilute acid pretreatment of biomass. Transgenic iron-accumulating Arabidopsis and rice plants exhibited higher iron content in grains, increased biomass yield, and importantly, enhanced sugar release from the biomass.ResultsIn this study, we used intracellular ferritin (FerIN) alone and in combination with an improved version of cell wall-bound carbohydrate-binding module fused iron-binding peptide (IBPex) specifically targeting switchgrass, a bioenergy crop species. The FerIN switchgrass improved by 15% in height and 65% in yield, whereas the FerIN/IBPex transgenics showed enhancement up to 30% in height and 115% in yield. The FerIN and FerIN/IBPex switchgrass had 27% and 51% higher in planta iron accumulation than the empty vector (EV) control, respectively, under normal growth conditions. Improved pretreatability was observed in FerIN switchgrass (~ 14% more glucose release than the EV), and the FerIN/IBPex plants showed further enhancement in glucose release up to 24%.ConclusionsWe conclude that this iron-accumulating strategy can be transferred from model plants and applied to bioenergy crops, such as switchgrass. The intra- and extra-cellular iron incorporation approach improves biomass pretreatability and digestibility, providing upgraded feedstocks for the production of biofuels and bioproducts.

Highlights

Pretreatments are commonly used to facilitate the deconstruction of lignocellulosic biomass to its component sugars and aromatics
Design of an improved Signal peptide (SP)‐Carbohydrate-binding module (CBM)‐iron-binding peptide (IBP) with enhanced iron‐binding ability To overcome the recalcitrance of switchgrass, we aimed to design an improved version of switchgrass based on the success of our previous study using model plants [81]
Two DNA fragments were synthesized encoding the triple fusion polypeptides, Production of transgenic switchgrass and molecular analyses Two DNA constructs were prepared: (1) intracellular ferritin (FerIN), and (2) FerIN stacking with cell wall targeting IBPex (FerIN/IBPex)

Summary

Introduction

Pretreatments are commonly used to facilitate the deconstruction of lignocellulosic biomass to its component sugars and aromatics. With the advancement of interdisciplinary expertise in “green” technology for second-generation biofuels, concepts for the lignocellulosic biorefinery have recently emerged and are defined as the sustainable processing of biomass and conversion to a wide range of bioenergy products (i.e., energy, heat, and biofuels) and other bioproducts (i.e., supplement, chemicals, and/or materials) [10,11,12]. The natural lignocellulosic networks are disrupted, which results in partial cell wall deconstruction, including wall delamination and defibrillation. These pretreated and modified walls are more readily attacked by lytic saccharification enzymes [32, 33]. The current barriers for the use of all known pretreatment technologies include the high energy inputs/waste outputs and complex nature of the resulting pretreated biomass and liquors [34,35,36]

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