Three cellulosomal xylanase genes in Clostridium thermocellum are regulated by both vegetative SigA (σA) and alternative SigI6 (σI6) factors

Clostridium thermocellum efficiently degrades crystalline cellulose by a high molecular weight protein complex, the cellulosome. The bacterium regulates its cellulosomal genes using a unique extracellular biomass-sensing mechanism that involves alternative sigma factors and extracellular carbohydrate-binding modules attached to intracellular anti-sigma domains. In this study, we identified three cellulosomal xylanase genes that are regulated by the sigma(I6)/RsgI6 system by utilizing sigI6 and rsgI6 knockout mutants together with primer extension analysis. Our results indicate that cellulosomal genes are expressed from both alternative sigma(I6) and sigma(A) vegetative promoters. (C) 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.