chromatium chromatium chromatium is a genus of photoautotrophic gram-negative bacteria which are found in water. the cells are straight rod-shaped or slightly curved. they belong to the purple sulfur bacteria and oxidize sulfide to produce sulfur which is deposited in intracellular granules of the cytoplasm. chromatium scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: chromatiales family: chromatiaceae genus: chromatiumperty 1852 type species chromatium okenii species c. buderi c. glycolicum c. gracile c. minus c. minutissimum c. okenii c. purpuratum c. salexigens c. tepidum c. vinosum c. violascens c. armingii c. weisii c. gracile