3.1.9. Chromatiaceae

Freshwater Chromatiaceae including *Chromatium*, *Allochromatium,* and *Thiocystis* species lack betaine and ectoine biosynthesis and corresponding transport systems (Table 3), Marine and halophilic Chromatiaceae can synthesize betaine from glycine and have the

BetT transport system, but lack ectoine biosynthesis. With the exception of *Marichromatium gracile* and *Thiorhodococcus drewsii*, betaine biosynthesis from choline is absent. The group of marine representatives including the *Marichromatium, Thiorhodococcus,* and *Imhoffiella* species, *Thiocapsa marina* and *Thiocystis violacea* DSM 208 has an *opuA* gene cluster, but lacks the ProW permease protein of ProU. An exception is *Thiorhodococcus minor,* which has a ProU (type W1) instead of the OpuA system (Table 3) like all other marine and halophilic Chromatiaceae.
