Effect of shear on morphology and erythromycin production in Saccharopolyspora erythraea fermentations

A complex medium was used to investigate the effects of shear on the S. ery thraea fermentation at 7-1 scale. Maximum biomass was 11.1 +/- 0.5 g l(-1) at 1250 rpm (tip speed = 4.45 ms(-1)), whereas it was 12.7 +/- 0.2 g l(-1) at 350 rpm (tip speed = 1.07 ms(-1)). Specific erythromycin production was not stirrer speed dependent in the range of 350 to 1000 rpm and decreased b y 10% at stirrer speed of 1250 rpm. Morphological measurements using image analysis showed that the major axis of the mycelia (both freely dispersed a nd clumps) decreased after the end of the rapid growth phase to a relativel y constant value (equilibrium size) dependent on the stirrer speed. The mec hanical properties of the cell wall were examined by disruption of fermenta tion broth in homogeniser and it was shown that mechanical strength of the cell wall increased in a large extent during deceleration phase.