The characterization of Clostridium beijerinckii NRRL B592 cells transformed with plasmids containing the butanol-production genes under the control of constitutive promoters

Clostridium beijerinckii is a spore-forming, obligate anaerobe that is capable of producing butanol, acetone and isopropanol. These industrial chemicals are traditionally known as solvents. The regulation of solventogenic fermentation is linked to the onset of sporulation, so that by the time the organism begins to produce solvents, it is also entering into spore formation and metabolic slowdown. The goal of this research project was to study the effect of placing the solvent-production genes from C. beijerinckii under the control of constitutive promoters from other genes, in an attempt to allow an earlier start of butanol production during the growth phase than is the case with the wild-type cells.

The aldehyde dehydrogenase from C. beijerinckii NRRL B593 (ald) and alcohol dehydrogenase from C. beijerinckii NRRL B592 (adhA) were placed under the control of the promoter from the acid-producing operon (the BCS operon) in one vector, and under the control of the promoter from the ferredoxin gene in another. In both cases, aldehyde dehydrogenase activity was produced earlier in the growth phase in transformed cells, but alcohol dehydrogenase activity was not.

The adhA gene from C. beijerinckii NRRL B592 was paired with the adhB gene from the same organism in a third vector, both under the control of the promoter from the BCS operon. In cells transformed with this vector, alcohol dehydrogenase activity was observed earlier in the growth phase than it was in wild-type NRRL B592 cells.