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There are two major shapes of bacteria, i.e., rod-shape and spherical shape. The genus Deinococcus consists of rod-shape and spherical shape species. The authors determined whether the common ancestor of Deinococcus was rod-shape or spherical.
The rod-shaped related proteins (MreB, MreC, MreD, MrdA, RodA, and RodZ)?have been identified. We compared the homologs of those proteins in various Deinococcus species and Thermus thermophilus. The evolutionary relationships among the Deinococcus species used in this study were shown by using comparison of their all ribosomal protein sequences.
D. actinosclerus, D. deserti, D. peraridilitoris, and D. puniceus had all the six rod-shape related genes. Homologs of mreC, mreD, and mrdA formed a conserved gene cluster, which were also conserved in T. thermophilus. Thus, although mrdA and rodA were found to be clustered in Escherichia coli, mrdA homolog was not clustered with rodA homolog in Deinococcus and T. thermophilus. Although mreB, mreC, and mreD were found clustered in E. coli, homologs of mreB, rodA, and rodZ were scattered in the genome of all the Deinococcus species.
Phylogenetic relationships inferred on the basis of rod-shape related genes showed that D. maricopensis and D. peraridilitoris had diverged prior to the separation of other Deinococcus species, which is in agreement with the evolution of Deinococcus species (phylogenetic relationships inferred from the ribosomal protein sequence comparison). The phylogenetic analyses indicated that major gene loss of the rod-shape related genes had occurred four times during the evolution of Deinococcus, which led to the generation of spherical shape species in the genus Deinococcus.
Our findings showed that each of the rod-shaped related genes had been inherited in most of rod-shaped species of Deinococcus during the evolution of Deinococcus species. Thus, the common ancestor of Deinococcus species was rod shaped.