Index >> Bacterial Photosynthesis >> Chlorobiaceae (Formerly Chlorobacteriaceae) Non Motile Green and Brown Sulphur Bacteria

Elemental sulphur is formed as an intermediate product of oxidation, and is excreted into the medium to form sulphur globules. Sulphur is then more or less completely oxidized to sulphate under conditions of limiting sulphide

The Chlorobiaceae characterized by the presence of chlorobium chlorophylls BChl, c or d which form the major components. In addition small amounts of B.Chl a are present. The reaction centre pigment is BChl a Carotenoids of group 5 form accessory pigments. In 1968 Pfenning identified two brown species, Chlorobium phaeobacteroides and Chlorobium, phaeovibrioides, and since then several brown species have been isolated.

In Chlorobium and Chloropseudomonas the primary photochemical reaction centre is P840. Electron transport chains of both cyclic and noncyclic photophosphorylation are found. Chlorobium thiosulfatophilum possesses ferredoxin (Fd) whose sole function appears to be reduction of NAD+. Rubredoxin has been found in C. thiosulfatophilum and Chloropseudomonas ethylicum, but Dot in the purple bacteria.

It appears to link bacterial and plant ferredoxins. Three types of quinones have been isolated from C. thiosulfatophilum and Chloropseudomonas ethylicum. Chlorobium quinone is present only in sulphide adapted cells. Polar menaquinone is believed to be a precursor of chlorobium quinone. Menaquinone-7 is the third quinone.