Bioconversion of dilute-acid pretreated sorghum bagasse to ethanol by Neurospora crassa

Abstract

Bioethanol production from sweet sorghum bagasse (SB), the lignocellulosic solid residue obtained after extraction of sugars from sorghum stalks, can further improve the energy yield of the crop. The aim of the present work was to evaluate a cost-efficient bioconversion of SB to ethanol at high solids loadings (16 % at pretreatment and 8 % at fermentation), low cellulase activities (1-7 FPU/g SB) and co-fermentation of hexoses and pentoses. The fungus Neurospora crassa DSM 1129 was used, which exhibits both depolymerase and co-fermentative ability, as well as mixed cultures with Saccharomyces cerevisiae 2541. A dilute-acid pretreatment (sulfuric acid 2 g/100 g SB; 210 °C; 10 min) was implemented, with high hemicellulose decomposition and low inhibitor formation. The bioconversion efficiency of N. crassa was superior to S. cerevisiae, while their mixed cultures had negative effect on ethanol production. Supplementing the in situ produced N. crassa cellulolytic system (1.0 FPU/g SB) with commercial cellulase and β-glucosidase mixture at low activity (6.0 FPU/g SB) increased ethanol production to 27.6 g/l or 84.7 % of theoretical yield (based on SB cellulose and hemicellulose sugar content). The combined dilute-acid pretreatment and bioconversion led to maximum cellulose and hemicellulose hydrolysis 73.3 % and 89.6 %, respectively.

Cellulosic Butanol (ABE) Biofuel Production from Sweet Sorghum Bagasse (SSB): Impact of Hot Water Pretreatment and Solid Loadings on Fermentation Employing Clostridium beijerinckii P260

“…There are several reports on the pretreatment of SSB employing dilute acid [42,43], SO 2 [16,44], alkali [45,46], lime [43], ammonia [28], and liquid hot water treatment [47][48][49]; two of them [47,50] are more relevant to the present studies. In these two reports, the authors used acetic acid pretreatment followed by SSB hydrolysis and fermentation to butanol [47,50].…”

A novel diffusion–biphasic hydrolysis coupled kinetic model for dilute sulfuric acid pretreatment of corn stover

“…Experimental studies of dilute sulfuric acid pretreatment have been performed using wheat straw (Rajan and Carrier, 2014), rice straw (Hsu et al, 2010), sorghum bagasse (Dogaris et al, 2012), rapeseed straw (Choi et al, 2013), sugarcane bagasse (Chen et al, 2011), sunflower stalks (Ruiz et al, 2013), and switchgrass (Shi et al, 2011). Because pretreatment experiments are frequently time-consuming, labor-intensive, and environmentally unfavorable, some efforts have also been dedicated to modeling dilute sulfuric acid hydrolysis kinetics of lignocellulose substrate.…”

Developing elite Neurospora crassa strains for cellulosic ethanol production using fungal breeding

“…While investigations aimed at understanding cellulolytic and fermentative systems, and even attempts at CBP have been made utilizing wild-type and gene deletion mutants of N. crassa , none have investigated natural variation due to allelic effects as a source of elite strains for CBP [8, 18, 27, 30, 31]. Here, we investigated variation in saccharification of cellulose and fermentation among natural and laboratory populations using model cellulose substrates to identify elite strains for CBP.…”