TABLE 1.

Genome size range and divergence in 16S rDNA for representative bacterial taxa

Organism	% 16S rDNA divergence	Genome size range (Mb)	% Difference in genome size	Source or reference (for genome size)
Free-living/opportunistic pathogens
Escherichia coli	<1	4.5–5.5	22	4
Salmonella typhi	<1	3.9–4.9	25	23
Bacillus cereus	1	2.4–5.3	121	5
Chronic pathogens
Spotted fever group of Rickettsia spp.	<3	1.2–2.1	75	21
Mycoplasma hominis	<1	0.70–0.83	19	14, 18
Mycoplasma genitalium-M. pneumoniae	2	0.58–0.82	41	9, 11
Chlamydia psittaci-C. trachomatis	5	1.0–2.65	165	10, 22
Vertically transmitted symbiont
Buchnera aphidicola	6–8	0.63–0.64	<3	7; this study