Table 1. Percent of hypervariable region tags from the RefSSU database that map to one or more taxa.

Hypervariable region V3
Number of Taxa	1	2	3	4	5+
Phylum	99.96% / 114328	0.04% / 42	0.00% / 42	0	0
Class	99.93% / 109352	0.07% / 77	0.00% / 2	0	0
Order	99.88% / 99682	0.12% / 113	0.00% / 4	0	0
Family	99.62% / 88015	0.34% / 297	0.04% / 34	0.00% / 3	0.00% / 3
Genus	99.11% / 69686	0.07% / 495	0.09% / 64	0.05% / 35	0.00% / 29
Hypervariable region V6
Number of Taxa	1	2	3	4	5+
Phylum	99.83% / 54728	0.17% / 94	<0.01% / 1	0	0
Class	99.68% / 51795	0.30% / 158	0.01% / 6	0	0
Order	99.30% / 45579	0.62% / 285	0.05% / 23	0.01% / 5	0.01% / 6
Family	98.77% / 40454	1.08% / 444	0.11% / 45	0.03% / 11	0.01% / 5
Genus	97.33% / 31463	2.07% / 670	0.35% / 112	0.15% / 50	0.01% / 31

For GAST to accurately identify microbial taxa, the same tag sequence must not be present in different taxa: each tag should only have one taxonomic source. Table 1 shows the percentage of hypervariable tags (V3 or V6) present in the RefSSU that map to single or multiple taxa. The results are displayed both as a percentage of tags and as a total number of tags.