期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 107, 期 43, 页码 18646-18651出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1012175107
关键词
biomass; carbohydrate binding modules; Clostridium regulation; glycoside hydrolases; anti-sigma factors
资金
- United States-Israel Binational Science Foundation [2005-186]
- State of Lower Saxony
- Technion-Niedersachsen Research Cooperation Program
- Erwin and Rosl Pollak Chair in Biotechnology at the Technion
- Volkswagen Foundation, Hannover, Germany
Clostridium thermocellum produces a highly efficient cellulolytic extracellular complex, termed the cellulosome, for hydrolyzing plant cell wall biomass. The composition of the cellulosome is affected by the presence of extracellular polysaccharides; however, the regulatory mechanism is unknown. Recently, we have identified in C. thermocellum a set of putative sigma and anti-sigma s factors that include extracellular polysaccharide-sensing components [Kahel-Raifer et al. (2010) FEMS Microbiol Lett 308:84-93]. These factor-encoding genes are homologous to the Bacillus subtilis bicistronic operon sigI-rsgI, which encodes for an alternative s I factor and its cognate anti-sigma(1) regulator RsgI that is functionally regulated by an extracytoplasmic signal. In this study, the binding of C. thermocellum putative anti-s I factors to their corresponding s factors was measured, demonstrating binding specificity and dissociation constants in the range of 0.02 to 1 mu M. Quantitative real-time RT-PCR measurements revealed three-to 30-fold up-expression of the alternative s factor genes in the presence of cellulose and xylan, thus connecting their expression to direct detection of their extracellular polysaccharide substrates. Cellulosomal genes that are putatively regulated by two of these s factors, sigma(I1) or sigma(I6), were identified based on the sequence similarity of their promoters. The ability of sigma(I1) to direct transcription from the sigI1 promoter and from the promoter of celS (encodes the family 48 cellulase) was demonstrated in vitro by runoff transcription assays. Taken together, the results reveal a regulatory mechanism in which alternative s factors are involved in regulating the cellulosomal genes via an external carbohydrate-sensing mechanism.
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