TURBULENT BREAKAGE OF FILAMENTOUS MICROORGANISMS IN SUBMERGED CULTUREIN MECHANICALLY STIRRED BIOREACTORS

A discussion is presented suggesting that hyphal breakage in mechanica lly stirred fermenters is likely to occur by direct tensile stresses a cting on the opposite ends of the hypha of filamentous microorganisms. These stresses originate from the dynamic pressure fluctuations of ed dies with scales in the inertial convection subrange of the turbulent energy spectrum. The maximum strain energy theory of failure of an ela stic material under this mode of stress is used to set up a relationsh ip between the stable length of hyphae and some of the physical parame ters affecting it, including the mean energy dissipation rate in the b ioreactor. Experimental data are reported for the rate of breakage of hyphae obtained under different operating conditions during the fermen tation of Penicillium chrysogenum in a 7 and 150 1 mechanically stirre d bioreactor. Data on the stable size of hyphae agree well with the mo del based on the maximum energy criterion. The experimental data furth er suggest that hyphal breakage is approximately a first-order kinetic process with a rate constant which appears to be moderately dependent on the product of the mean energy dissipation rate and the reciprocal of the impeller circulation time.