What was the name of the first bacterium shown to acquire hereditary traits through transformation?

Streptococcus pneumoniae was the first bacterium shown to acquire hereditary traits through transformation.

In 1928, Frederick Griffith studied two strains of the pneumococcus bacterium. Smooth, capsule-forming bacteria caused disease in mice, whereas rough bacteria lacking the capsule did not. When heat-killed smooth cells were mixed with living rough cells, the mice died and living smooth bacteria were recovered.

Griffith called the process transformation and proposed that a transferable substance changed the harmless bacteria. In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty identified that substance as DNA.

Transformation is now understood as uptake of external DNA by a cell followed by its maintenance or incorporation. It is distinct from transduction, which uses bacteriophages, and conjugation, which transfers DNA through cell-to-cell contact.