Xylanase and cellulase systems of Clostridium sp.: An insight on molecular approaches for strain improvement

• Genetic engineering tools appear interesting for strain improvement for clostridia for CBP.
• Genes encoding enzymes of solvent pathways have been cloned and sequenced for clostridia.
• Their expression has been correlated with the pattern of end-product formation in fermentations.
• CBP offers potential benefits for the production of biofuels from lignocellulose.
• Clostridia appear the best choice for CBP.

Bioethanol and biobutanol hold great promise as alternative biofuels, especially for transport sector, because they can be produced from lignocellulosic agro-industrial residues. From techno-economic point of view, the bioprocess for biofuels production should involve minimal processing steps. Consolidated bioprocessing (CBP), which combines various processing steps such as pretreatment, hydrolysis and fermentation in a single bioreactor, could be of great relevance for the production of bioethanol and biobutanol or solvents (acetone, butanol, ethanol), employing clostridia. For CBP, Clostridium holds best promise because it possesses multi-enzyme system involving cellulosome and xylanosome, which comprise several enzymes such as cellulases and xylanases. The aim of this article was to review the recent developments on enzyme systems of clostridia, especially xylanase and cellulase with an effort to analyse the information available on molecular approaches for the improvement of strains with ultimate aim to improve the efficiencies of hydrolysis and fermentation.