Table 4.

Probability that g20 sequence clusters are non-random with respect to the salinity at the site from which they were collected.

Environmental category	Salinity (ppt)	# Sequences	Unifrac P-value
Sewage	N/A	6	≤ 0.0001
Fresh	< 0.50	149	≤ 0.0001
Estuarine	0.5–17.99	6	0.0096
Brackish	18–32.99	183	0.1456
Ocean	33–38	286	0.0006
Hypersaline	> 38	8	0.0474

The Unifrac distance metric (Lozupone et al., 2006) was used for the analysis. Salinity values, when not available from the published work, were obtained from the communicating author of the paper in which the g20 sequence was first reported. All freshwater samples were assumed to have a salinity of < 0.50 ppt. All but the sequences from brackish waters clustered non-randomly (P< 0.05) with respect to the habitat type as defined by salinity.