Characteristics[edit]
The Alphaproteobacteria is a diverse order and comprises several phototrophic genera, several genera metabolising C1-compounds (e.g., Methylobacterium spp.), symbionts of plants (e.g., Rhizobium spp.), endosymbionts of arthopods (Wolbachia) and intracellular pathogens (eg. Rickettsia). Moreover the class includes (as an extinct member) the protomitochondrion, the bacterium that was engulfed by the eukaryotic ancestor and gave rise to the mitochondria, which are organelles in eukaryotic cells (See endosymbiotic theory).[2] A species of technological interest is Rhizobium radiobacter (formerly Agrobacterium tumefaciens): scientists often use this species to transfer foreign DNA into plant genomes.[5] Aerobic anoxygenic phototrophic bacteria, such as Pelagibacter ubique, are alphaproteobacteria that are a widely distributed marine plankton that may constitute over 10% of the open ocean microbial community.