Enrichment and Isolation Procedures

A prerequisite for the successful enrichment and isolation of Thiopedia species is the use of an inoculum from anoxic water or mud samples in which the characteristic Thiopedia platelets were microscopically detected. For the isolation of pure cultures, it is advisable to prepare enrichment cultures in liquid media, as well as agar shake dilution cultures that are directly inoculated from the sample of the natural habitat. In liquid media, Thiopedia may be outgrown by other purple sulfur bacteria containing gas vesicles.

The culture medium and incubation conditions are similar to those described for Chromatium species. Not more than 1.5 mM sulfide and 3 mM acetate should be used for growth of Thiopedia, and the trace element solution must not contain a chelating agent (e.g., EDTA). Growth is enhanced by the addition of 100 |M dithionite to the medium. Incubation is carried out at a temperature of 20-25°C and a light intensity of 100-200 lux. Thiopedia species grow in the form of individual cells, or platelets with 4-128 cells. Colonies and cell suspensions of Thi-opedia rosea exhibit a unique bright purple-red color and can, therefore, be differentiated readily from other purple sulfur bacteria.

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