Abstract
Corynebacterium species are members of gram-positive bacteria closely related to
Mycobacterium species, both of which are classified into the same taxonomic order Actinomycetales. Recently, three corynebacteria,
Corynebacterium efficiens, Corynebacterium glutamicum, and
Corynebacterium diphtheriae have been sequenced independently. We found that the order of orthologous genes in these species has been highly conserved though it has been disrupted in
Mycobacterium species. This synteny suggests that corynebacteria have rarely undergone extensive genome rearrangements and have maintained ancestral genome structures even after the divergence of corynebacteria and mycobacteria. This is the first report that the genome structures have been conserved in free-living bacteria such as
C. efficiens and
C. glutamicum, although it has been reported that obligate parasites such as
Mycoplasma and
Chlamydia have the stable genomes. The comparison of recombinational repair systems among the three corynebacteria and
Mycobacterium tuberculosis suggested that the absence of
recBCD genes in corynebacteria be responsible for the suppression of genome shuffling in the species. The genome stability in
Corynebacterium species will give us hints of the speciation mechanism with the non-shuffled genome, particularly the importance of horizontal gene transfer and nucleotide substitution in the genome.