The industrially important bacterium Clostridium acetobutylicum is characterized by its biphasic fermentation metabolism: at high pH-values, it produces the acids butyrate and acetate, and lowering the pH leads to drastic changes in the metabolism, whereas the acids are converted to the neutral solvents butanol and acetone.
In a systematic approach employed here, comprehensive analyses of the cell growth with its characteristic products, accompanying proteome (2D PAGE) and transcriptome (DNA micro array) data were compared at different pH values using chemostat cultures. This study elucidates the critical pH value where the metabolic change takes place and the organism switches between acid and solvent production. Moreover, key proteins and genes of acidogenic and solventogenic cells were identified. A knock-out mutant of a potential key protein of acidogenic cells, which presumably plays a significant role in the metabolic switch, was investigated at different pH values regarding growth, proteome and transcriptome. Using additional butanol stress experiments, transcription patterns of specific genes related to the presence of butanol or lowering the pH value, respectively, were exhibited.
In conclusion, this study provides a global view of protein and transcription patterns of chemostat cells at different pH values and provides new insights of the metabolic switch of C. acetobutylicum.