Turbulent breakage of the S. erythraea filamentous actinomycete has been studied using a 7 L laboratory scale and a 450 1 pilot scale mechanically stirred fermenter. A model of hyphal breakage is set up based on stress cycling (fatigue) resulting from continuous recirculation of the mycelia through the high stress zone of the impeller. The model is based on the critical strain energy criterion of failure reported by the authors in a previous publication. However, in the present study, the mycelium is assumed to have fractal properties and the individual hypha is assumed to behave elastically with a wall thickness which is assumed to increase linearly with the distance away from the growing tip. The experimental data obtained as part of this study and the limited results on the breakage of filamentous actinomycete from the literature are used to examine the general applicability of the model equation. The analysis shows reasonable agreements.