Transcriptomic analysis of Clostridium thermocellum ATCC 27405 cellulose fermentation

Babu Raman, Catherine K. McKeown, Miguel Rodriguez, Steven D. Brown, Jonathan R. Mielenz

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Abstract

Background: The ability of Clostridium thermocellum ATCC 27405 wild-type strain to hydrolyze cellulose and ferment the degradation products directly to ethanol and other metabolic byproducts makes it an attractive candidate for consolidated bioprocessing of cellulosic biomass to biofuels. In this study, whole-genome microarrays were used to investigate the expression of C. thermocellum mRNA during growth on crystalline cellulose in controlled replicate batch fermentations. Results: A time-series analysis of gene expression revealed changes in transcript levels of ∼40% of genes (∼1300 out of 3198 ORFs encoded in the genome) during transition from early-exponential to late-stationary phase. K-means clustering of genes with statistically significant changes in transcript levels identified six distinct clusters of temporal expression. Broadly, genes involved in energy production, translation, glycolysis and amino acid, nucleotide and coenzyme metabolism displayed a decreasing trend in gene expression as cells entered stationary phase. In comparison, genes involved in cell structure and motility, chemotaxis, signal transduction and transcription showed an increasing trend in gene expression. Hierarchical clustering of cellulosome-related genes highlighted temporal changes in composition of this multi-enzyme complex during batch growth on crystalline cellulose, with increased expression of several genes encoding hydrolytic enzymes involved in degradation of non-cellulosic substrates in stationary phase. Conclusions: Overall, the results suggest that under low substrate availability, growth slows due to decreased metabolic potential and C. thermocellum alters its gene expression to (i) modulate the composition of cellulosomes that are released into the environment with an increased proportion of enzymes than can efficiently degrade plant polysaccharides other than cellulose, (ii) enhance signal transduction and chemotaxis mechanisms perhaps to sense the oligosaccharide hydrolysis products, and nutrient gradients generated through the action of cell-free cellulosomes and, (iii) increase cellular motility for potentially orienting the cells' movement towards positive environmental signals leading to nutrient sources. Such a coordinated cellular strategy would increase its chances of survival in natural ecosystems where feast and famine conditions are frequently encountered.

Original languageEnglish
Article number134
JournalBMC Microbiology
Volume11
DOIs
StatePublished - 2011

Funding

The authors would like to thank Meghan Drake for assistance with qRT-PCR studies, and Brian Davison and Dale Pelletier for critically reviewing the manuscript and for providing valuable feedback. This work was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory and through the BioEnergy Science Center (BESC). BESC is a U.S. Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. Oak Ridge National Laboratory is managed by UT-Battelle LLC for the U.S. D.O.E. under contract no. DE-AC05-00OR22725.

FundersFunder number
BioEnergy Science Center
U.S. Department of Energy Bioenergy Research Center
Office of Science
Biological and Environmental Research
Oak Ridge National Laboratory
UT-BattelleDE-AC05-00OR22725

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