Current ideas on the nature and development of the chromatophores of photosynthetic bacteria are reviewed. A simple method of obtaining purified chromatophores by sucrose density gradient centrifuging of cell-free extracts of
Rhodopseudomonas spheroides
is described. Such preparations consist of about 60% protein, 20% phospholipid and 10% pigment, most of which is bacteriochlorophyll. Small quantities of carbohydrate, but only traces of nucleic acid, are found. The material was fairly homogeneous on electron microscopy.
Rps. spheroides
was also grown under pure oxygen in the dark. A particulate preparation from cells cultured under these conditions was similar to the chromatophores with respect to its high content of protein and of phospholipid but had a much greater content of nucleic acid and no bacteriochlorophyll. In addition, it contained amino sugars and diaminopimelic acid which are not found in chromatophores. These differences in chemical composition were correlated with the electron microscope appearances of the different subcellular fractions. It is concluded that the particulate preparation from cells grown under oxygen represents the cytoplasmic membrane of the micro-organism, but as isolated it is heavily contaminated with fragments of the cell wall from which it cannot be readily separated.
Isolation and characterization of low nucleic acid (LNA)-content bacteria
