Genome sequence and comparative analysis of the solvent-producing bacterium Clostridium acetobutylicum

The genome sequence of the solvent-producing bacterium Clostridium acetobut ylicum ATCC 824 has been determined by the shotgun approach. The genome con sists of a 3.94-Mb chromosome and a 192-kb megaplasmid that contains the ma jority of genes responsible for solvent production. Comparison of C. acetob utylicum to Bacillus subtilis reveals significant local conservation of gen e order, which has not been seen in comparisons of other genomes with simil ar, or, in some cases closer, phylogenetic proximity. This conservation all ows the prediction of many previously undetected operons in both bacteria. However, the C. acetobutylicum genome also contains a significant number of predicted operons that are shared with distantly related bacteria and arch aea but not with B. subtilis. Phylogenetic analysis is compatible with the dissemination of such operons by horizontal transfer. The enzymes of the so lventogenesis pathway and of the cellulosome of C. acetobutylicum comprise a new set of metabolic capacities not previously represented in the collect ion of complete genomes. These enzymes show a complex pattern of evolutiona ry affinities, emphasizing the role of lateral gene exchange in the evoluti on of the unique metabolic profile of the bacterium. Many of the sporulatio n genes identified in B. subtilis are missing in C. acetobutylicum, which s uggests major differences in the sporulation process. Thus, comparative ana lysis reveals both significant conservation of the genome organization and pronounced differences in many systems that reflect unique adaptive strateg ies of the two gram-positive bacteria.