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The nutritional requirements of limnic bacterial populations were determined using the methods developed by Lochhead and co-workers. Samples were taken from Ekoln (one of the basins of Lake Malaren) and from the central part of Lake Hjalmaren. Many of the isolated bacteria from the spring and summer samples required organic nitrogen, only a few showed maximal growth in media with only inorganic nitrogen. During late autumn and winter the requirements of the bacteria were simpler and about 50 % required only inorganic nitrogen. Throughout the year most of the bacteria needed vitamins or other growth factors. The requirements of bacterial populations isolated from the two lakes were different. Bacteria requiring yeast extract and/or peptone were most common when phytoplankton (diatoms) was abundant. Not all bacteria showed significant growth density within a 5 day period at 20'C. The requirements of the slower growing bacteria were different from those of the other bacteria. The former needed yeast extract and peptone to a greater degree than the fast-growing types. Pe3ioMe IHccneJAoBanH nliHeLBbIe HOTpe6HOCTH 03epHbIX |
