Rj. Fischer et al., CLONING, SEQUENCING, AND MOLECULAR ANALYSIS OF THE SOL OPERON OF CLOSTRIDIUM-ACETOBUTYLICUM, A CHROMOSOMAL LOCUS INVOLVED IN SOLVENTOGENESIS, Journal of bacteriology, 175(21), 1993, pp. 6959-6969
A DNA region of Clostridium acetobutylicum contiguous with the adc ope
ron has been cloned and sequenced. Structural genes encoding the aceto
acetyl coenzyme A:acetate/butyrate:coenzyme A transferase (ctfB and ct
fA) and an alcohol/aldehyde dehydrogenase (adhE) could be identified.
These three genes together with a small open reading frame (ORF) of un
known function (upstream of adhE) formed an operon (sol operon), as sh
own by mRNA analyses. The complete sol operon was transcriptionally in
duced or derepressed before the onset of solventogenesis, thus confirm
ing earlier results of Northern hybridizations with a ctfB gene probe
(U. Gerischer and P. Durre, J. Bacteriol. 174:426-433, 1992). Upstream
of the sol operon, we identified two putative promoters that were loc
ated in regions with possible stem-loop structures formed by several i
nverted repeats. The distal promoter P1 showed only minor transcriptio
n initiation in solventogenic C acetobutylicum cells but was recognize
d in Escherichia coli, presumably because of its high similarity to th
e sigma70 consensus sequence. The adhE-proximal promoter P2 directed t
he major transcription start point in solventogenic C acetobutylicum b
ut was not recognized in E. coli. The clostridial AdhE showed high sim
ilarity to a novel family (type III) of alcohol dehydrogenases. Two ot
her ORFs (ORF 5 and ORF 6) were found on the cloned DNA region that sh
owed no significant similarity to sequences in various available data
bases. mRNA studies revealed that ORF 5 formed a monocistronic operon
and showed increased expression before onset of solventogenesis.