Bacteria identified that were domesticated for cellular power packs billions of year ago. Update.

Power packs are the magenta structures.

A common family of marine bacteria (SAR11) has been identified as a genetic source for the power packs inside every living cell (mitochondria).   It's been known for some time that cells must have swallowed some bacteria billions of years ago and domesticated them on the inside to provide energy.  Connecting the dots to specific bacteria is the news. "An astounding evolutionary event".     Mitochondria described here.

Representation of one mitochondrion.
Bacterial relic.

Story at Science Daily News
Added: Related story at Wired Science: Human Cells a Chimera of Ancient Life

UPDATE September 19th:  The SAR11 family contains 30% of the bacteria population in the oceans and operates on a fraction of its original genome. The DNA research into SAR11 turned up a hitherto unknown type of bacteria whose protein package resembles that of mitochondria.  "They are very similar to mitochondria. Our findings thus indicate that the origin of mitochondria might be the oceans, but that they are not related to the SAR11 group as was previously thought," says Thijs Ettema.