Enrichment and Isolation Procedures

Media and culture conditions are the same as described for Chro-matium species. Lamprocystis species, like other purple sulfur bacteria containing gas vesicles, may be selectively enriched by making use of the buoyancy of their cells at lower temperatures of 4-10°C (Pfennig et al., 1968). For enrichment cultures, an inoculum from a natural habitat, in which the presence of Lam-procystis cells and cell aggregates was established microscopically, should be used. The culture medium and incubation conditions are the same as described for the genus Chromatium. Low sulfide concentrations (1-2 mM) and low light intensity (100-300 lux) with diurnal light and dark periods (e.g., 18 h light, 6 h dark) are employed at a room temperature of about 20°C. The bottles are incubated in a lying position to avoid accumulation of cells in the nonilluminated area under the screw cap. After two or three supplementations of the enrichment culture with neutralized sulfide solution, the well-developed culture is stored in a refrigerator in an upright position. This is not done until the various types of purple sulfur bacteria have almost completely oxidized the sulfur globules inside the cells. After 1-2 weeks of storage at a temperature between 4 and 10°C, purple sulfur bacteria with gas vesicles, including Lamprocystis species, accumulate at the surface of the liquid medium under the screw cap. A small amount of the floating material is removed with an inoculation loop and inspected microscopically under brightfield illumination. For further enrichment, the floating cell mass is carefully pipetted from the surface and transferred to fresh medium. Alternatively, or in addition, the enriched material is used to inoculate one or two series of agar shake cultures as described for the isolation of Chromatium species.

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