Solventogenic enzymes of Clostridium acetobutylicum: catalytic properties, genetic organization, and transcriptional regulation

Abstract

The enzymes acetoacetate decarboxylase and coenzyme A transferase catalyse acetone production from acetoacetyl-CoA in Clostridium acetobutylicum. The adc gene encoding the former enzyme is organized in a monocistronic operon, while the ctf genes form a common transcription unit with the gene (adhE) encoding a probable polyfunctional aldehyde/alcohol dehydrogenase. This genetic arrangement could reflect physiological requirements at the onset of solventogenesis. In addition to AdhE, two butanol dehydrogenase isozymes and a thiolase are involved in butanol synthesis. RNA analyses showed a sequential order of induction for the different butanol dehydrogenase genes, indicating an in vivo function of BdhI in low level butanol formation. The physiological roles of AdhE and BdhII most likely involve high level butanol formation, with AdhE being responsible for the onset of solventogenesis and BdhII ensuring continued butanol production. Addition of methyl viologen results in artificially induced butanol synthesis which seems to be mediated by a still unknown set of enzymes. Although the signal that triggers the shift to solventogenesis has not yet been elucidated, recent investigations suggest a possible function of DNA supercoiling as a transcriptional sensor of the respective environmental stimuli.

Toxins, Butyric Acid, and Other Short-Chain Fatty Acids Are Coordinately Expressed and Down-Regulated by Cysteine in Clostridium difficile

“…The enzyme 3-hydroxybutyryl-CoA dehydrogenase was among the most prominent cysteine-regulated proteins. This enzyme is involved in fatty acid metabolism, particularly the production of butyric acid and butanol (solventogenesis) in C. acetobutylicum (5,22). Solventogenesis is a process in C. acetobutylicum cultures in which certain SCFAs become converted to ketones and alcohols.…”

“…Solventogenesis is linked to sporulation in this organism, and mutants unable to convert, e.g., butyric acid to butanol sporulate poorly (15). Conversion of accumulated acids (acidogenesis) to solvents (solventogenesis) is probably induced to detoxify the acidic environment, and this process enables the bacteria to complete endospore formation and survive (5). Solventogenesis can thus be considered to be a stress response, and, in parallel with solvent-producing enzymes, heat shock proteins are induced (19).…”

Acetone and Butanone Metabolism of the Denitrifying Bacterium "Aromatoleum aromaticum" Demonstrates Novel Biochemical Properties of an ATP-Dependent Aliphatic Ketone Carboxylase

“…They are produced in several biological processes, for example, during solvent fermentation by many Clostridia, which produce acetone by decarboxylation of acetoacetate (6,9). Moreover, both compounds are heavily used as solvents or synthetic precursors in industry and constitute significant groundwater contaminants due to their high solubility in water.…”

Control of Butanol Formation in Clostridium acetobutylicum by Transcriptional Activation

“…It has been proposed that the sol operon is controlled by two promoters, based on primer extension studies (9,21). The sequence of the putative distal promoter, designated P 1 or S 2 , exhibited almost perfect homology to the consensus sequence of housekeeping promoters (just one mismatch), whereas the sequence of the putative proximal promoter (P 2 or S 1 ) had at least five mismatches (in the 12 nucleotides comprising the Ϫ35 and Ϫ10 regions) and unusual spacing of the two promoter boxes (8,9,21). Nevertheless, based on signal intensities obtained in primer extension experiments, most of the transcripts are initiated at this transcription start point (9).…”