Microbial conversion of cellulose to sugars by bacterial enzyme

Abstract

This work studied the conversion of lignocellulosic materials to sugars, the intermediates for bioethanol production, by a bacterial enzyme. Due to the complex structure of lignocellulose, a cellulase enzyme cannot effectively access and hydrolyse cellulose fibers. Various pretreatment processes of lignocellulose have been studied to enhance enzymatic hydrolysis to date. In this work, corncob was firstly studied for microbial pretreatment using three microorganisms including two bacterial strains of Bacillus subtilis A 002 and Cellulomonas sp. TISTR 784 and a fungal strain of Phanerochaete sordida SK7. The results showed that the microbial pretreatment with P. sordida SK7 was the most effective for enhancing enzymatic hydrolysis with approximately 40% improvement, compared to no treatment. Whereas, Bacillus subtilis A 002 was able to hydrolyse some cellulose fraction in lignocellulose but the reducing sugar concentration was very low due to its simultaneously consumption. In the following part, the native cellulase-producing bacteria B. subtilis was developed to produce enzyme at high level using PCR-based cloning technique. Endoglucanse gene encoding from B. subtilis M015 was cloned into plasmid (pFLAG-CTS) and transferred into E. coli JE5505. The clone, named E. coli Glu5, could greatly produce endoglucanase with higher enzymatic activity than that of the native strain, approximately 17 times. Finally, E. coli Glu5 was used for a microbial hydrolysis of soluble cellulose (carboxymethyl cellulose) in a continuous bubble reactor. The results demonstrate the feasibility to consolidate the steps of enzyme production and enzymatic hydrolysis together in continuous system at a low organic loading rate of 5 kg/m3d.