thermochromatium thermochromatium thermochromatium is a gram-negative and thermophilic genus of bacteria from the family of chromatiaceae with one known species (thermochromatium tepidum). the habitats of thermochromatium tepidum are hot springs which contain sulfide. thermochromatium tepidum was first isolated from the mammoth hot springs from the yellowstone national park in the united states. thermochromatium scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: chromatiales family: chromatiaceae genus: thermochromatiumimhoff et al. 1998 type species thermochromatium tepidum species t. tepidum