Ref ID : 1167
Hans Gude; Grazing by protozoa as selection factor for activated sludge bacteria. Microbial Ecology 5:225-237, 1979
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In continuous culture enrichments that were inoculated with activated sludge and were fed with polymeric substrates, freely dispersed single-celled bacteria belonging to the Cytophaga group dominated among the initial populations, irrespective of the activated sludge source. These populations were grazed by flagellated protozoa which after several days reached high cell densities. Other morphologic bacterial groups such as spiral-shaped or filamentous bacteria then became dominant. In defined mixed culture experiments with bacterial isolates from the enrichment cultures, it was shown that a "grazing-resistant" Microcyclus strain outgrew a Cytophaga strain in the presence of grazing protozoa. In contrast, the Cytophaga strain competed successfully with the Microcyclus strain and with other "grazing-resistant" strains under protozoa-free conditions. Furthermore, it was demonstrated that assumed grazing resistance factors such as floccing or filamentous growth were lost by some of the strains when they were grown for several generations in continuous culture under the same conditions, but in the absence of protozoa.