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Genome-wide gene expression analysis of the switch between acidogenesis and solventogenesis in continuous cultures of Clostridium acetobutylicum

Abstract (Expand)

Clostridium acetobutylicum is able to switch from acidogenic growth to solventogenic growth. We used phosphate-limited continuous cultures that established acidogenic growth at pH 5.8 and solventogenic … growth at pH 4.5. These cultures allowed a detailed transcriptomic study of the switch from acidogenesis to solventogenesis that is not superimposed by sporulation and other growth phase-dependent parameters. These experiments led to new insights into the physiological role of several genes involved in solvent formation. The adc gene for acetone decarboxylase is upregulated well before the rest of the sol locus during the switch, and pyruvate decarboxylase is induced exclusively for the period of this switch. The aldehyde-alcohol dehydrogenase gene adhE1 located in the sol operon is regulated antagonistically to the paralog adhE2 that is expressed during acidogenic conditions. A similar antagonistic pattern can be seen with the two paralogs of thiolase genes, thlA and thlB. Interestingly, the genes coding for the putative cellulosome in C. acetobutylicum are exclusively transcribed throughout solventogenic growth. The genes for stress response are only induced during the shift but not in the course of solventogenesis when butanol is present in the culture. Finally, the data clearly indicate that solventogenesis is independent from sporulation.

Authors: Christina Grimmler, , , , , , Wolfgang Liebl,

Date Published: 6th Jan 2011

Publication Type: Not specified

A systems biology approach to investigate the effect of pH-induced gene regulation on solvent production by Clostridium acetobutylicum in continuous culture

Abstract (Expand)

Background: Clostridium acetobutylicum is an anaerobic bacterium which is known for its solvent-producing capabilities, namely regarding the bulk chemicals acetone and butanol, the latter being a highly … efficient biofuel. For butanol production by C. acetobutylicum to be optimized and exploited on an industrial scale, the effect of pH-induced gene regulation on solvent production by C. acetobutylicum in continuous culture must be understood as fully as possible. Results: We present an ordinary differential equation model combining the metabolic network governing solvent production with regulation at the genetic level of the enzymes required for this process. Parameterizing the model with experimental data from continuous culture, we demonstrate the influence of pH upon fermentation products: at high pH (pH 5.7) acids are the dominant product while at low pH (pH 4.5) this switches to solvents. Through steady-state analyses of the model we focus our investigations on how alteration in gene expression of C. acetobutylicum could be exploited to increase butanol yield in a continuous culture fermentation. Conclusions: Incorporating gene regulation into the mathematical model of solvent production by C. acetobutylicum enables an accurate representation of the pH-induced switch to solvent production to be obtained and theoretical investigations of possible synthetic-biology approaches to be pursued. Steady-state analyses suggest that, to increase butanol yield, alterations in the expression of single solvent-associated genes are insufficient; a more complex approach targeting two or more genes is required.

Editor:

Date Published: 2011

Publication Type: Not specified

A proteomic and transcriptional view of acidogenic and solventogenic steady-state cells of Clostridium acetobutylicum in a chemostat culture

Abstract (Expand)

The complex changes in the life cycle of Clostridium acetobutylicum, a promising biofuel producer, are not well understood. During exponential growth, sugars are fermented to acetate and butyrate, and … in the transition phase, the metabolism switches to the production of the solvents acetone and butanol accompanied by the initiation of endospore formation. Using phosphate-limited chemostat cultures at pH 5.7, C. acetobutylicum was kept at a steady state of acidogenic metabolism, whereas at pH 4.5, the cells showed stable solvent production without sporulation. Novel proteome reference maps of cytosolic proteins from both acidogenesis and solventogenesis with a high degree of reproducibility were generated. Yielding a 21% coverage, 15 protein spots were specifically assigned to the acidogenic phase, and 29 protein spots exhibited a significantly higher abundance in the solventogenic phase. Besides well-known metabolic proteins, unexpected proteins were also identified. Among these, the two proteins CAP0036 and CAP0037 of unknown function were found as major striking indicator proteins in acidogenic cells. Proteome data were confirmed by genome-wide DNA microarray analyses of the identical cultures. Thus, a first systematic study of acidogenic and solventogenic chemostat cultures is presented, and similarities as well as differences to previous studies of batch cultures are discussed.

Authors: , , , Birgit Voigt, Michael Hecker, ,

Date Published: 1st Aug 2010

Publication Type: Not specified

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