thiococcus thiococcus thiococcus is a gram-negative, non‐motile, obligately phototrophic and strictly anaerobic genus of bacteria from the family of chromatiaceae with one known species (thiococcus pfennigii). thiococcus pfennigii was first isolated from salt marshes. thiococcus scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: chromatiales family: chromatiaceae genus: thiococcusimhoff et al. 1998 type species thiococcus pfennigii species t. pfennigii