Maintenance Procedures

Pure cultures of Chromatium species can be maintained in the defined mineral medium, preferably in 100-ml screw-capped bottles. The freshly grown cultures are supplemented with neutralized sulfide solution to a final concentration of 1.5 mM, and kept in the light for about 2 h until the cells have formed intracellular sulfur globules. At this stage, the stock cultures can be stored at 4°C for 2-3 months. The cultures keep well if they are put back under dim light at room temperature and supplemented again with neutralized sulfide solution. After formation of sulfur globules, the cultures are put back into the refrigerator.

Long-term preservation of Chromatium species is successfully performed by storage in liquid nitrogen. For this purpose, dense cell suspensions of liquid cultures are supplemented with DMSO as a protective agent to a final concentration of 5%, using an autoclaved 50% DMSO stock solution. Such suspensions are dispensed into 2-ml plastic ampules, which are then sealed and freeze-stored. Chromatium species do not survive lyophilization and cannot be preserved in this way.

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