1. Chromatium gracile forms pure colonies in agar column, and when a pure colony is transfered into VAN NIEL'S solution, the growth of the bacteria takes place in a completely anaerobic condition. The organisms form pure colonies in a plate agar when the culture is enclosed in the gas which consists of H₂S, CO₂ and H₂ in the proportion 1:2:27.
2. As the nitrogenous source ammonium salts are more suitable for the growth of the purple sulphur bacteria than nitrates. Ammonium salts are effective for the growth of the organisms in the next order: NH₄NO₃> NH₄Cl>(NH₄)₂SO₄>(NH₄)₂HPO₄. Nitrates favourably affect the growth of the organisms in the next order: NH₄NO₃>NaNO₃>KNO₃> Ca(NO₃)₂.
3. NaHCO₃ and Na₂CO₃ are most suitable as a source of carbon, but in the absence of carbonates carbohydrates may be used by the organisms.
4. The pH-range under which the purple sulphur bacteria can develop is 6.0-8.0, and the optimum is 7.0 The pH-value of medium increases with the development of the purple sulphur bacteria. When Na₂CO₃ or NaHCO₃ are used as a source of carbon the rise of pH-value is remarkable, but if carbohydrates are used it is almost unchanged.
5. The ultra red light is most effective for the growth of the purple sulphur bacteria.