Coimmobilized aerobic/anaerobic mixed cultures in shaked flasks

The freely suspended aerobic fungus, Aspergillus awamori, and the anaerobic bacterium, Zymomonas mobilis were cultivated in synthetic medium in a stirred tank reactor. Their immobilized monocultures and coimmobilized mixed cultures were cultivated in shaked flasks in synthetic medium on various substrates. The biological variables of the freely suspended and immobilized monocultures were determined on soluble potato starch, maltose and glucose as substrates, respectively. In the coimmobilized mixed culture the fungus, which grows in the outer aerobic shell and the surface of the beads, converts the starch and maltose to glucose. Glucose is consumed by both of the microorganisms. Z. mobilis growing in the anaerobic core of the beads, converts a part of glucose to ethanol. The influence of the spore concentration of the fungus, bacterial inoculum amount and the kind of substrate on the cell growth and ethanol formation were evaluated. Repeated batch cultivation was maintained for 200 h.