[New methods for the observation and isolation of unusual or little known water bacteria].

Abstract

Techniques are described which allow the direct observation of water bacteria in their unchanged environment. Bacteria attaching to and growing on glass slides were observed with a partially submerged light microscope. Similarly, undisturbed living bacteria were studied in previously submerged PERFIL'EV glass capillaries, a necessity in the case of the fragile Gallionella or Metallogenium spp. Many new bacterial forms and surface structures were discovered when formvar-coated electron microscope grids were used as the substrate for attached growth („Aufwuchs”). Several water bacteria can be obtained by covering slides with layers of agar media and coating these with thin, transparent plastic foil to encourage specific attachment. The foil was used like a cover slip on water agar-coated slides. After microscopic observation the foil was peeled off and the colonies observed previously could then be isolated. Growth of pure cultures was successfully attempted in disposable Nalgene membrane filter units or in membrane-covered chambers which had been submerged in the aquatic environment to facilitate nutrient and waste exchange with the outside. Natural bacterial populations could be transferred with only little disturbance from stratified sediments to the laboratory. This was achieved by keeping aquaria in the water for an extended period of time to allow for re-establishment of the normal layering. During transportation, the aquaria were covered with plastic plates. In the laboratory some of the environmental factors such as the proper temperature and light were restored. With this method layered populations of even rare water bacteria could be kept alive for several months. Finally, an agar diffusion gradient plate is described. It enables one to grow and isolate unusually demanding, i.e. „stenobiotic” bacteria.