Fig. 2.

Evolutionary relationships determined using 554 base pairs of the portal protein gene (g20) from 769 available g20 sequences. Clusters defined by Zhong and colleagues (2002) are identified as culture-based clusters I–III and environmental-sequence-only clusters A–F. New clusters defined since Zhong and colleagues (2002) are indicated with the preface ‘new cluster’, a number and a brief description. The tree shown is the consensus (majority rules) tree from 11 GARLI iterations inferred using the maximum likelihood criterion (see Experimental procedures), with the Aeromonas phage Aeh1 g20 sequence used as an outgroup to root the tree. Three colour rings reflect the habitat type from which the g20 sequence originated. For most of these sequences (GOS sequences), there is ribotype dot-blot and metagenomic information about the microbial community structure at the site, while for non-GOS sequences such information was assumed where reasonable to do so (see Table 3 legend). The inner ring is the microbial community structure information listed as Rusch and colleagues (2007)-defined environmental categories, while the other two rings reflect the temperature and salinity of the original sampling site.