Table 2. Average nucleotide composition (mean% ± SE) of whole genomes and 16S rRNA genes of mesophiles and thermophiles.

Nucleotide	Mesophile	Thermophile	Significancea
(A) Nucleotide composition of entire genome, for the 31 genomes listed in Table 1
A	27.2 ± 1.47	27.8 ± 1.26	NSb
C	22.8 ± 1.48	22.1 ± 1.26	NS
G	22.8 ± 1.46	22.2 ± 1.22	NS
T	27.2 ± 1.47	27.8 ± 1.22	NS
(B) Nucleotide composition of 16S rRNA genes
A	26.1 ± 0.38	20.3 ± 0.41	P < 0.001
C	21.6 ± 0.31	28.8 ± 0.49	P < 0.001
G	30.5 ± 0.38	36.0 ± 0.47	P < 0.001
T	21.8 ± 0.31	14.9 ± 0.55	P < 0.001

^aProbability of Mann–Whitney U-test of respective nucleotide composition in the two sets of mesophiles and thermophiles.

^bNS, not significant (P > 0.5).