Table 1.

An example showing how Bray-Curtis dissimilarity was calculated between strain I and strain J. (Note: dissimilarity calculation in real case would be more complex because typical microbial genomes usually comprise thousands of genes)

Orthologous groups	# genes mapped in strain I	# genes mapped in strain J	C n *	C ij #	S i $	S j %	BC ij&
OG1	1	1	1	7	9	11	0.3
OG2	2	4	2
OG3	4	2	2
OG4	0	2	0
OG5	2	2	2

^* C _n was the number of common genes assigned to the same orthologous group, the lesser number of mapped genes was used

^# C _ij was the sum of C _n, and represented the total number of genes assigned to common orthologous groups between strain I and J

^$ S _i was the total number of genes in strain I mapped to orthologous groups in eggNOG database

^% S _j was the total number of genes in strain J mapped to orthologous groups in eggNOG database

& BC _ij is the Bray-Curtis dissimilarity between strain I and J