ABSTRACT
Abstract Clostridium acetobutylicum and C. beijerinckii are able to produce industrially important solvents such as acetone, butanol, and 2-propanol. The respective enzymes are induced shortly before the transition from exponential to stationary growth phase. The bacteria thus counteract the deleterious effects of butyric and acetic acids that had been synthesized during active growth. Regulation of solventogenesis is closely coupled to that of sporulation, a developmental program that guarantees long-time survival. Five operons are meanwhile known that are essential for acetone and butanol synthesis. Their regulation is complex, involving probably several transcription factors (among them SpoOA, the master regulator of sporulation), RNA processing, and co-or posttranslational modification of the gene product. DNA supercoiling plays an important role in signal transduction. Solventogenesis is also coupled to the stress response and a number of other metabolic reactions, as revealed by RNA analyses, two-dimensional gel electrophoresis, and DNA microarrays. Characterization of the genes and the still growing understanding of their regulation has allowed the metabolic engineering of recombinant strains with improved solvent formation ability and with clostridial genes for the production of commercially important polyesters.
