The genome of Carsonella ruddi was found in special cells inside an insect.  It is the smallest genome of any known living creature.

With only about 160,000 base pairs of DNA, the genome of Carsonella ruddi [image] is less than half the size thought to be the minimum necessary for life.

"It's the smallest genome, not by a bit but by a long way," said study team member Nancy Moran of the University of Arizona.

An organism's genome carries all of the instructions it needs to make the proteins required for life. Carsonella's genome codes for 182 proteins. The human genome, by comparison, contains about 3 billion DNA base pairs and codes for about 35,000 proteins.

Carsonella lives inside a leaf-munching insect, called a psyllid [image]. They have a symbiotic relationship. The bacteria's sheltered life has allowed it to pare its genome down to the bare minimum. There are certain genes necessary for life that the bacteria's genome lacks, but these are compensated for by its insect host.