Diverse sophisticated phylogenetic analyses update the phylogeny of the Alphaproteobacteria and show that the parasitic Holosporales is a derived group within the Rhodospirillales order which comprises primarily free-living alphaproteobacteria.

A number of microbial eukaryotes have adapted to low oxygen conditions by acquiring a gene that allows their mitochondrial electron transport chain to continue to function when oxygen is scarce.