FIG. 2.
Phylogenetic analysis of nifH genes obtained from oceanic picoplankton and zooplankton included in α, β, and γ proteobacteria and cyanobacterial clades. The tree includes nifH sequences representing cultivated organisms (genus and species) and uncultivated organisms (e.g., from termites and from marine [e.g., Tomales Bay] samples) (GenBank sequence numbers are indicated). The data set was bootstrapped 100 times, and bootstrap values greater than 50% are indicated at the relevant nodes (distance and parsimony methods are represented by values above and below the nodes, respectively). Sample information and identifications are given in Table 1. GP, gram positive; •, diatom associated; ⧫, picoplankton; 
, zooplankton associated.