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Clostridium thermocellum cellulosomal genes are regulated by extracytoplasmic polysaccharides via alternative sigma factors.
- Source :
-
Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2010 Oct 26; Vol. 107 (43), pp. 18646-51. Date of Electronic Publication: 2010 Oct 11. - Publication Year :
- 2010
-
Abstract
- 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 σ and anti-σ 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 σ(I) factor and its cognate anti-σ(I) regulator RsgI that is functionally regulated by an extracytoplasmic signal. In this study, the binding of C. thermocellum putative anti-σ(I) factors to their corresponding σ factors was measured, demonstrating binding specificity and dissociation constants in the range of 0.02 to 1 μM. Quantitative real-time RT-PCR measurements revealed three- to 30-fold up-expression of the alternative σ 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 σ factors, σ(I1) or σ(I6), were identified based on the sequence similarity of their promoters. The ability of σ(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 σ factors are involved in regulating the cellulosomal genes via an external carbohydrate-sensing mechanism.
- Subjects :
- Amino Acid Sequence
Bacterial Proteins genetics
Bacterial Proteins metabolism
Base Sequence
Cellulose metabolism
DNA, Bacterial genetics
Gene Expression Regulation, Bacterial
Gene Expression Regulation, Enzymologic
Kinetics
Models, Biological
Molecular Sequence Data
Operon
Promoter Regions, Genetic
Sigma Factor genetics
Thermodynamics
Cellulase genetics
Cellulase metabolism
Clostridium thermocellum genetics
Clostridium thermocellum metabolism
Genes, Bacterial
Multienzyme Complexes genetics
Multienzyme Complexes metabolism
Polysaccharides, Bacterial metabolism
Sigma Factor metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1091-6490
- Volume :
- 107
- Issue :
- 43
- Database :
- MEDLINE
- Journal :
- Proceedings of the National Academy of Sciences of the United States of America
- Publication Type :
- Academic Journal
- Accession number :
- 20937888
- Full Text :
- https://doi.org/10.1073/pnas.1012175107