Predation of bacteria by the protozoa Tetrahymena pyriformis in toluene-degrading cultures

The influence of the toluene concentration on predation of toluene-degradin g bacteria by the protozoa Tetrahymena pyriformis was investigated in suspe nded batch cultures continuously aerated with toluene-contaminated air. At gas phase concentrations of 0.035 to 0.74 g m(-3), toluene did not signific antly affected protozoan activity and the final bacteria concentration was reduced by growing protozoa by 98 to 99.9% compared to protozoa-free contro ls. As the toluene concentration was increased to 1.16-1.33 g m(-3), the re duction of the bacteria cell concentration was 80%. At 3.35 g toluene m(-3) , growth of T. pyriformis was completely inhibited. Overall, the results pr esented herein demonstrate that protozoa grazing on bacteria play a major r ole in controlling bacterial cell concentration, but that the toxicity of t he treated pollutants to the protozoa is an important factor that needs to be taken into account in biological treatment processes.