Which bacterium was the first organism whose complete genome was published, in 1995?

Haemophilus influenzae was the first free-living organism to have its complete genome published, in 1995.

The landmark sequence came from strain Rd and was reported by a team led by J. Craig Venter and Claire Fraser. The genome contained about 1.83 million base pairs and approximately 1,740 protein-coding genes. Its publication demonstrated that automated DNA sequencing could produce a complete microbial genome rather than isolated gene fragments.

H. influenzae is a small Gram-negative bacterium that can inhabit the human respiratory tract. Some strains cause disease, including meningitis and respiratory infections, while the nonencapsulated strain used for sequencing was a laboratory strain. Its name is historically misleading: the bacterium was incorrectly blamed for the 1918 influenza pandemic before influenza viruses were understood. The genome project helped launch comparative genomics, allowing scientists to examine which genes are essential, how bacteria evolve, and why related strains differ in disease-causing ability.