FIG 4 .
Distribution of nitrogen assimilation genes in the Alphaproteobacteria. Maximum likelihood tree constructed with concatenated 16S-23S rRNA genes. Most members of the SAR11 clade (highlighted in red) and some Alphaproteobacteria that are intracellular parasites (blue) are missing the PII genes glnB and glnK. Monophyletic groups in which all members had the same pattern of genes present and absent were collapsed, except for SAR11. Bootstrap values (n = 1,000) are indicated at the nodes. The scale bar indicates 0.1 change per position. “+” indicates at least one homolog present in the genome, while “−” indicates that no homolog was identified.