Isolation of Members of the Family Rhodospirillaceae
The purple nonsulfur bacteria (Rhodospirillaceae) comprise different morphological types of photo-trophic bacteria that can photoassimilate simple organic compounds under anaerobic conditions. They are also capable of chemotrophic growth under aerobic con
- PDF / 1,591,960 Bytes
- 7 Pages / 595.32 x 790.92 pts Page_size
- 53 Downloads / 268 Views
Isolation of Members of the Family Rhodospirillaceae HANNa BIEBL and NORBERT PFENNIG
The purple nonsulfur bacteria (Rhodospirillaceae) comprise different morphological types of phototrophic bacteria that can photoassimilate simple organic compounds under anaerobic conditions. They are also capable of chemotrophic growth under aerobic conditions, but not all species develop under full atmospheric oxygen tension. At oxygen concentrations between 0.5% and 5%, photosynthesis and oxidative metabolism may function simultaneously. Although several species would grow under aerobic conditions at rates comparable to those observed under anaerobic phototrophic conditions, incubation with organic substrates in the light with oxygen excluded is the only way to enrich selectively for the purple nonsulfur bacteria. The first enrichment procedures (Molisch, 1907; see also van Niel, 1971) made use of the natural decomposition processes of organic matter to liberate adequate nutrients and to provide anaerobic conditions. Solid organic material of plant, or preferably, animal origin such as hay, seagrass, boiled eggs, smashed bones, dead aquatic or soil animals were put onto the bottom of glass cylinders and covered with mud. The cylinders were filled with river water, and placed in diffuse daylight. Reddish brown coloration of the water was observed after several weeks. Later authors separated and immobilized the material to be decomposed with a layer of soil and sand (Buder, 1919; Schneider, 1930). It was van Niel's merit to elaborate a physiological basis for the enrichment of purple nonsulfur bacteria (van Niel, 1944). He developed a defined medium that contained a single organic compound and only small amounts of a complex substrate as a source for growth factors. Furthermore, he introduced closed bottles as culture vessels and incubated in continuous light. By appropriate choice of the carbon source, the species composition of the enrichment could be influenced to some extent (see also: Drews, 1965; Pfennig, 1967; Pfennig, Eimhjellen, and Liaaen-Jensen, 1965; Scher, Scher, and Hutner, 1963; van Niel, 1971). For isolation, a diluted sample of the enrichment culture was inoculated in agar tubes (Schneider, 1930) or plated on agar surfaces by later authors (Drews, 1965). M. P. Starr et al. (eds.), The Prokaryotes © Springer-Verlag Berlin Heidelberg 1981
In this contribution a third method, which does not require an enrichment step in liquid medium, is recommended and described in detail (Biebl and Drews, 1969; Swoager and Lindstrom, 1971). The sample from nature is directly inoculated into or onto a solid medium so as to allow each cell of purple nonsulfur bacteria to develop separately. The method avoids the outgrowth of some species by other species that regularly prevail in liquid enrichments. The colonies of Rhodospirillaceae that appear after anaerobic incubation in the light are easily recognized by their strong pigmentation. Membrane filters are used when the expected cell density of Rhodospirillaceae is low. When the med
Data Loading...
