Change of mycelial morphology in tylosin production by batch culture of Streptomyces fradiae under various shear conditions

Morphological change during culture of the tylosin producer Streptomyces fradiae under various shear conditions was investigated using an image analysis system. The morphology was classified as filament, entangled filament, or pellet by measuring the mycelial area and convex perimeter. At fermentor agitation rates of 400 rpm and higher, filament and entangled filament morphology comprised more than 50%. However, in cultures at agitation rates lower than 400 rpm, pellet morphology increased gradually and until it comprised more than 50%; in an air-lift reactor, the pellet ratio reached 80% after 160-h culture. The average areas of pellets and mycelia in the air-lift reactor were respectively 100- and 20-fold those under high shear condition. Both pellet area and mycelial morphology changed during the culture period according to the shear conditions. Among the various shear conditions, tylosin production and rapeseed oil consumption were lowest in the airlift fermentor culture with against in the fermentor at 400 rpm. From the viewpoint of tylosin production, the optimal mycelial area that gave the maximum production rate under various shear conditions was around 4 × 103 μm2. When the mycelia and pellet areas exceeded 4 × 103 μm2, the tylosin production rate decreased drastically.