Why Sequence Rhodobacter sphaeroides?

How can a photosynthetic bacterium help us understand a fundamental question in evolutionary biology? The acquisition and loss of genetic information permits the adaptation of an organism to an ever-changing environment. However, this genetic flux is a double-edged sword. On the one hand, it permits the acquisition of new adaptive traits, but this process may result in the damage or loss of functioning genetic systems, with possibly dire consequences for the individual or species. How can such genomic plasticity occur without being severely disruptive to the ongoing lifestyle of an organism?  One possible solution to this dilemma is the presence of genomic “safe zones,” where the insertion or deletion of DNA is not disruptive to the genome at large. Such safe zones may also provide a “molecular workshop,” where genetic tinkering may permit the evolution of novel traits to meet the demands of environmental change. The photoheterotrophic bacterium Rhodobacter sphaeroides possesses two chromosomes, one of which contains a high density of information content.  The second, chromosome II, has a much lower coding density and could serve as a reservoir for the exchanges and manipulations described above. This hypothesis will be tested by sequence comparisons of chromosome II from six to ten different isolates of Rhodobacter sphaeroides.  Researchers will be looking for genetic content differences between these chromosomes. Such differences may include the relative numbers and types of essential and nonessential genes, the age of genes (i.e., recently acquired vs. more ancient genes), breakpoints where genetic exchanges occur, and a mechanism by which these exchanges could take place. These findings should relate directly to the origin and evolution of the microbial genome and are likely to have mechanistic implications for the evolution of the eukaryotic cell.

CSP project participants: Samuel Kaplan (proposer, Univ. of Texas Med. School, Houston) and Timothy J. Donohue (proposer, Univ. of Wisconsin-Madison).

Genome Portal Sites: Rhodobacter sphaeroides ATCC17025 and Rhodobacter sphaeroides ATCC17029