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Cat M. Haglund studied the bacterial protein Sca2 as a mediator of actin-based movement in Rickettsia. The work identified formin-like activity, connecting a bacterial surface protein with the assembly of host actin filaments.^[ref]

Rickettsia is a genus of intracellular bacteria, many associated with arthropods. Some species cause disease in vertebrate hosts, but a genus name does not identify one universal vector, disease or cellular mechanism. Dependence on host cells makes retained and lost metabolic functions especially informative.

The genome of Rickettsia prowazekii contains respiratory and citric-acid-cycle machinery alongside extensive biosynthetic losses. Comparisons with mitochondrial gene sets helped investigate the bacterial ancestry of mitochondria. ^[ref] Shared features and a reconstructed relationship are evidence about evolutionary history; they do not make a living rickettsial species the unchanged ancestor of every modern mitochondrion.