Fig. 2: Evolution of (semi-)essential amino acid (AA) biosynthesis pathways in Donaciinae symbionts.

a Comparison of symbiont genomes across 26 species of Donaciinae. Phylogenomic tree represents the relationships among symbionts, based on an alignment of 49 marker genes. Blue and magenta arrowheads indicate methionine and tryptophan biosynthesis genes, respectively, that have been lost in the symbionts of particular host taxa. Coloring of genes is the same as in Fig. 1f, g. b Schematic AA biosynthesis pathways as well as glycolysis and TCA cycle in reed beetle symbionts, with important intermediates and enzymes highlighted. Enzymatic steps in green are present across all symbiont genomes, those in gray are absent from all genomes. Colored steps indicate loss of enzymatic steps in particular taxa (see legend). Amino acids are colored according to the inferred capacity of the symbionts to produce them. Note that the loss of ilvE in Macroplea is assumed to be compensated for by alternative symbiont or host enzymes²².