3.2.1. Chromatiaceae

Among the phototrophic *Gammaproteobacteria*, marine and halophilic phototrophic *Chromatiaceae* and *Ectothiorhodospiraceae* species have the ability to produce betaine from glycine. Marine and halophilic species encoding this pathway of betaine biosynthesis are found in different phylogenetic lineages with (a) the halophilic species of the genus *Halochromatium*, *Lamprobacter modestohalophilus*, *Thiohalocapsa halophila* forming one branch and (b) the marine species of *Marichromatium, Thiocapsa*, *Thiorhodococcus*, *Thiorhodovibrio,* and *Thiocystis violacea* DSM 208, *Rhabdochromatium marinum*, together with *Thiococcus pfennigii* and *Thioflavicoccus mobilis*, forming a second one (Figure 1). In both of these branches of *Chromatiaceae,* including the separate lineages of *Thiohalobacter thiocyanaticus* and *Imhoffiella purpurea*, just the two methyltransferases (GMT and DMT) form a distinct gene cluster (Table 3).
