methanophilic bacteria

butyric acid bacteria

Streptococcus lactin.

can induce root nodules on many plant species

can fix nitrogen in the free-living state

cannot fix specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids

like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex.

observable characteristics of existing organisms

the ancestral lineage of existing organisms

dendrogram based on DNA characteristics.

sexual characteristics.

DNA is not present at any stage in the life cycle of retroviruses.

Retroviruses carry gene for RNA-dependent DNA polymerase.

The genetic material in mature retroviruses is RNA.

Retroviruses are causative agents for certain kinds of cancer in man.