can be salt tolerant enough to grow in coastal habitats. Thiocapsa roseopersicina and Lamprocystis roseopersicina are among the well-known species of this group; the first one lacks gas vesicles, while in the second one gas vesicles and flagella-dependent movements occur. Marichromatium spp. and Thiorhodococcus spp. They are typical marine bacteria and capable of flagellar movements, but they differ from each other for their cell shape, which is rod and spherical, respectively. The species Thiophaeococcus mangrovi is associated to this group. The fourth group is phylogenetically more distant to the others and is composed by halophilic (Halochromatium spp. and Thiohalocapsa spp.), marine (Thiorhodovibrio spp., Rhabdochromatium spp. and Isochromatium spp.) and bacteriochlorophyll b-containing genera (Thiococcus spp., Thioflavicoccus spp. and Thioalkalicoccus spp.). Some species belonging to the last three genera are characterized by the presence of tubular internal membranes, a feature which distinguishes them from all the other genera of the family Chromatiaceae, which instead have internal membrane systems arranged as vesicles. Distinctive features There is a great variety among Chromatiaceae species. From a physiological and morphological point of view, individual members can be distinguished from each other on the basis of cell size and shape (sphere, rod, vibrio, spirillum), motility (polar flagella-dependent motility or nonmotile members), presence of gas vesicles and ability to form cellular aggregates. Unlike Ectothiorhodospiraceae and Chlorobiaceae bacteria, which store elemental sulfur outside their cells, the intracellularly formed elemental sulfur by Chromatiaceae bacteria gives them great advantages. The chemical element, as it is inaccessible to other bacteria, could serve as a useful personal reserve: of electron donors for photosynthesis in the case of external sulfide depletion; of electron acceptors for endogenous respiration in the absence of light (dark, oxic conditions); of electron acceptors for endogenous fermentation in the absence of both light and oxygen (dark, anoxic conditions). Regarding their photosynthetic pigment composition, in the Chromatiaceae can be found bacteriochlorophyll a or b and different types of carotenoids, according to the species. They confer to these bacteria their characteristic pigmentation, and if the amount of cells in the medium is high enough, the coloring may also be visible to the naked eye. Most of them have bacteriochlorophyll a, with a maximum absorption wavelength of 800-900 nm, and a number of species uniquely biosynthesize the red-colored aromatic carotenoid okenone. Okenone has an absorption peak around 500 nm and is involved in both photosynthesis and photoprotection. Bacteriochlorophylls and carotenoids are part of