Researchers Find Smallest Cellular Genome

Here's another thing to remember in case you're at a party and running our of conversational ideas. The living creature (other than viruses) with the smallest number of genes is the bacterium Carsonella ruddii – just 182 genes and 159,662 base-pairs of DNA.

Researchers Find Smallest Cellular Genome

The bacteria Carsonella ruddii has the fewest genes of any cell. The bacteria's newly sequenced genome, the complete set of DNA for the organism, is only one-third the size of the previously reported "smallest" cellular genome.

"It's the smallest genome -- not by a bit but by a long way," said co-author Nancy A. Moran, UA Regents' Professor of ecology and evolutionary biology and a member of the National Academy of Sciences. "It's very surprising. It's unbelievable, really. We would not have predicted such a small size. It's believed that more genes are required for a cell to work."

Carsonella ruddii has only 159,662 base-pairs of DNA, which translates to only 182 protein-coding genes, reports a team of scientists from The University of Arizona in Tucson and from Japan.

Of course, C. ruddii is cheating a little. It lives only in certain specialized cells of a sap-eating insect (Pachypsylla venusta). The bacterium has no genes needed for certain enzymes (required for replication) and nutrients such as folic acid, so it must rely on its host for these. Consequently, C. ruddii is not a good guide for identifying a minumum set of genes needed for a free-living organism.

If you want to sound really well-informed about this, here are some other things to read:

Bacteria boast the 'tiniest genomes' to date – New Scientist

Tiny Genome May Reflect Organelle in the Making – Scientific American

Smallest Genome of Living Creature Discovered – LiveScience

The 160-Kilobase Genome of the Bacterial Endosymbiont Carsonella and The Bacterial World Gets Smaller – Science [subscription rqd. for full access]

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