In genetics, which organism had the first complete genome sequence published for a free-living organism?

In genetics, Haemophilus influenzae had the first complete genome sequence published for a free-living organism. The landmark sequence was reported in 1995 and contained 1,830,140 base pairs.

The bacterium’s genome was sequenced by whole-genome shotgun sequencing, an approach in which DNA is broken into many small fragments, each fragment is sequenced, and computer programs assemble the overlapping pieces. The project demonstrated that an entire microbial genome could be read without mapping every region first.

The published H. influenzae genome contained 1,743 protein-coding genes, along with genes for structural RNAs and other genetic functions. It was a major milestone in genomics because it provided a complete catalogue of the genetic instructions of a free-living organism.

People sometimes confuse this achievement with the first genome sequence of any organism. Viral genomes had been sequenced earlier, while H. influenzae was the first free-living organism to receive a complete published genome sequence. Mycoplasma genitalium followed in 1995 with a smaller genome.