The bacterium Rhodobacter sphaeroides, shown here undergoing cell division,belongs to the a-subdivision of the Proteobacteria. This group of bacteria are among the most metabolically diverse organisms known, being capable of growing in a wide variety of growth conditions. For example, R. sphaeroides possesses an extensive range of energy acquiring mechanisms including photosynthesis, lithotrophy, aerobic and anaerobic respiration. It can also fix molecular nitrogen, synthesize important tetrapyrroles, chlorophylls, heme, and vitamin B12.

It has extremely facile methodologies for genetic manipulations, gene transfer, genetic analyses, chromosomal mobilization, etc. In addition, R. sphaeroides 2.4.1 has been shown to detoxify a number of metal oxides and oxyanions and is the subject of ongoing studies on bioremediation. R. sphaeroides 2.4.1 is also the first free living bacterium known to utilize the regulatory systems associated with quorum-sensing. Other recent findings reveal that the methods of motility and environmental sensing in relation to bacterial taxis, and  movement in R. sphaeroides, are unique both genetically and physiologically.  This organism also possesses a number of traits and characteristics which show interesting similarities to those of the mammalian mitochondrion.

There are several natural isolates of R. sphaeroides, and most of those currently identified as R. sphaeroides appear to possess two chromosomes. The R. sphaeroides 2.4.1 genome consists of two circular chromosomes, chromosome I (CI, ~3.0 Mbp), chromosome II (CII, ~0.9 Mbp), and five other replicons. The advent of molecular genetic techniques and their uses in studying this organism has faciliated complex and detailed analyses of gene regulation and expression, but has also permitted genome analyses of this species. In our genome project, a large amount of DNA sequence data was obtained from the R. sphaeroides 2.4.1 genome for both chromosomes. There is now a substantial amount of data showing sequence duplication and divergence of genes on CI and CII. The complex genome architecture and considerable gene duplication in R. sphaeroides add an entirely new dimension to microbial diversity, microbial evolution, and the possible evolution of diploid-systems.