Technically Speaking: Alpha-Proteobacteria

The evolution of Eukaryotes is thought to have resulted from several major symbiotic events. This technical document describes the alpha-proteobacteria as an important initial source of genetic diversity among eukarya, as described in the background of this article. Ancestral relatives of these germs are thought to have provided the original mitochondrion.

The alpha-proteobacteria are a highly intriguing group, being identified in Rickettsia and subcuticular bacteria, a poorly understood endosymbiont in marine invertebrates. Furthermore, alpha-proteobacteria are thought to be the cause of juvenile oyster disease (JOD).

So, the alpha-proteobacteria are thought to 1) have been the precursor to eukaryotic mitochondria, 2) are curious, poorly understood endosymbionts of at least one highly successful phylum of marine invertebrates, and 3) are causative agents of disease in both marine organisms and man. But, there's more. One diverse group of alpha-Proteobacteria are those belonging to the genus Wolbachia. This intracellular symbiont is known to occur among a wide array of arthropods, often affecting the reproductive fitness of their hosts. More on Wolbachia can be found here. There is much current research involving genome mapping of Wolbachia from a variety of hosts archived in massive databases.

Are these microbes providing us a modern picture of earliest evolutionary events from which life diversified? Are there any examples of alpha-proteobacteria that are not pathogenic/parasitic, but rather represent a symbiont in a commensal or mutually beneficial arrangement?