Evidence for HGT of RubisCO form 1A to the common ancestor of the Paulinella chromatophore and α-cyanobacteria. The ML tree was inferred from RubisCO large subunit (rbcL) form 1 amino acid sequences (470 aligned positions) of Paulinella chromatophora, cyanobacteria, plastids and proteobacteria under the RtREV+I+Γ model of amino acid substitution. Numbers at branches are ML bootstrap values ≥ 50%. Strain designations (when available) and NCBI accession numbers are indicated after the species name. Newly determined sequences are given in bold. Greek letters in grey indicate α-, β-, or γ- proteobacteria. Arrowheads highlight strains for which the gene arrangement of the carboxysomal operon is shown in Figure 5.