Table 1.

Number and percentage of bacterial genomes with each nucleotide showing the least at each codon position^a.

	A		T		C		G
	Genome number	Genome percentage	Genome number	Genome percentage	Genome number	Genome percentage	Genome number	Genome percentage
Firstb	0	0	13,872	69.7	6,039	30.3	0	0
Second	176	0.9	0	0	3	0.0	19,732	99.1
Third	10,496	52.7	827	4.2	6,224	31.3	2,364	11.9

^aFor each genome, we calculated frequency of four nucleotides at each codon position and chose the least nucleotides for this genome.

^bTaking the first codon position as an example, we explain the meaning of the genome number and genome percentage. As we know, a total of 19,911 genomes are involved. Among them, 13,872 genomes have T as the least nucleotide out of the four nucleotides at the first codon position and 6,039 genomes have C as the least nucleotide at this codon position. No genomes have A and G as the least nucleotide at this position. In other words, T constitutes the least nucleotides at the codon position in more genomes than A, C, and G.

The bold values indicate the least nucleotides at each codon position.