These bacteria were discovered by the German microbiologist Klaus Heckmann in the cytoplasm of the ciliate Euplotes aediculatus and designated as Omikron (Omicron in English literature).
[2] In 1987 Omikron / Omicron was scientifically described by Klaus Heckmann and Helmut Schmidt as the new species (and genus) Polynucleobacter necessarius.
[3] Later free-living Polynucleobacter bacteria were discovered in the water columns of lakes and ponds.
These planktonic, non-endosymbiontic members of the genus Polynucleobacter were initially assigned to a new subspecies of the species P. necessarius [4] but later transferred to separate species.
This is in contrast to other species of the genus Polynucleobacter, which exclusively harbour free-living bacteria dwelling in the water column of freshwater systems (lake, ponds, puddles and running waters).