Sawdust-Induced Production of Xylanases and Cellulases for Biofuel Applications

Abstract

This study evaluated the potential of sawdust as an inducer of carbon for the production of lignocellulolytic (cellulase and xylanase) enzymes by filamentous fungi for biofuel applications. Fourteen soil samples were collected from a phosphate mine in Phalaborwa, South Africa. Filamentous fungi were isolated from these samples using cellulose and xylose media. These isolateswere tested qualitatively and quantitatively for endocellulase and xylanases. Four isolates were found to have promising xylanase activity and these were identified as Amesia atrobrunnea, Penicillium citrinum, Rhizopus azygosporus and Aspergillus quadrilineatus using ITS1/2 sequencing. A time-course assay for xylanase activity revealed that R. azygosporus and A. quadrilineatus exhibited the highest activity. The crude enzymes were extracted from these strains and used for the enzymatic saccharification of the untreated sawdust. The total reducing sugars were estimated using the DNS method. The results for the enzymatic saccharification showed that a high total reducing sugar concentration of 2.35 g/L was released by 20 U/g of crude xylanases from A. quadrilineatus after 60 h of hydrolysis, while the synergistic hydrolysis of sawdust with the commercial cellulase, Celic CTec2, and the crude enzyme of 6 U/g from A. quadrilineatus showed the maximum concentration of total reducing sugars of 1.41 g/L after 72 h. Sawdust proved to be an effective inducer of xylanase production, although it was less effective for cellulase. This study reports that the commercial cellulase was outperformed by the crude enzymes during hydrolysis, highlighting the possibility that commercial enzymes may be replaced by microbial enzymes, thus lowering the environmental hazards of chemical formulations. Sugar yields could potentially be improved through biomass pretreatment, enzyme purification and strain improvement.