Unrooted maximum likelihood amino-tree of DNA polymerase A with sequences from amplicons (Labonté et al., 2009; Breitbart et al., 2004), as well as phage isolates and metagenomic sequences. Bootstrap values are indicated as black (90% to 100%) or gray (70% to 89%) dots at the nodes (100 replicates). The groups are labeled as follows: P-60, marine cyanopodoviruses; T7, Enterobacter podoviruses; SIO1-like, Roseobacter viruses. PUP clade was identified by Breitbart et al. (2004), Env clade 1–3 were identified by Labonté et al. (2009). Env-4 was identified by Schmidt et al. (2014). Env 5 is a new environmental clade that includes cyanophage S-EIV1. Scale bar represents amino-acid substitutions per site.