Growth and expression of relevant metabolic genes of Clostridium thermocellum cultured on lignocellulosic residues

Abstract

The plant cell wall is a source of fermentable sugars in second-generation bioethanol production. However, cellulosic biomass hydrolysis remains an obstacle to bioethanol production in an efficient and low-cost process. Clostridium thermocellum has been studied as a model organism able to produce enzymatic blends that efficiently degrade lignocellulosic biomass, and also as a fermentative microorganism in a consolidated process for the conversion of lignocellulose to bioethanol. In this study, a C. thermocellum strain (designated B8) isolated from goat rumen was characterized for its ability to grow on sugarcane straw and cotton waste, and to produce cellulosomes. We also evaluated C. thermocellum gene expression control in the presence of complex lignocellulosic biomasses. This isolate is capable of growing in the presence of microcrystalline cellulose, sugarcane straw and cotton waste as carbon sources, producing free enzymes and residual substrate-bound proteins (RSBP). The highest growth rate and cellulase/xylanase production were detected at pH 7.0 and 60 °C, after 48 h. Moreover, this strain showed different expression levels of transcripts encoding cellulosomal proteins and proteins with a role in fermentation and catabolic repression.

Digestibility of Wheat and Cattail Biomass Using a Co-culture of Thermophilic Anaerobes for Consolidated Bioprocessing

“…It is thought that the purpose of these hemicellulases and pectinases is to remove the polysaccharides covering the favoured cellulose beneath [203]. While each individual cellulosome appears to be composed of nine randomly selected cellulosomal proteins, one for each cohesin/dockerin link [202], C. thermocellum does change overall expression levels of its cellulosomal proteins based on factors such as carbon source [204][205][206][207]. C. thermocellum is known to release cellulosomes from its cell surface during later stages of cell growth [208,209] allowing for hydrolysis to continue.…”

Streptomyces thermocerradoensis I3 secretes a novel bifunctional xylanase/endoglucanase under solid‐state fermentation

“…In hardwood the hemicellulose is composed of about 15–30% of xylan and between 7 and 10% in softwood . Its complete degradation requires the combined action of endo‐1,4‐β‐xylanase (EC 3.2.1.8) and xylan 1,4‐β‐xylosidase (EC 3.2.1.37) …”

“…4 Its complete degradation requires the combined action of endo-1,4-β-xylanase (EC 3.2.1.8) and xylan 1,4-β-xylosidase (EC 3.2.1.37). 5 The cost of enzyme production is a major limitation in their biotechnological applications. For example, since the cost of enzymes in ethanol production is high ($ 0.68/gal), significant efforts need to be put to lower the component of enzyme cost in biofuel production.…”

Produção de hidrogênio e ácidos orgânicos a partir do bagaço de cana-de-açúcar e licor de pentoses em reatores em batelada com consórcio de microorganismos autóctones

“…O-Thong et al (2008) investigaram a relação C/N e a concentração de ferro na produção de biohidrogênio e ácidos orgânicos em reatores batelada em pH inicial 5,5 e temperatura 37 ºC usando planejamento experimental e MSR. Neste estudo foram utilizadas águas residuárias de óleo de palma como substrato.…”

“…Pattra et al (2008) estudaram os efeitos do pH inicial e da concentração inicial de carboidratos totais (licor de pentoses gerado a partir do pré-tratamento do BCA com H 2 SO 4 ) na produção de biohidrogênio por Clostridium butyricum. Os experimentos foram conduzidos em reatores batelada e temperatura de 37 ºC.…”