MODELING OF HIGH CELL-DENSITY FED-BATCH CULTIVATION

Escherichia coli was grown in carbon- and energy source-limited fed ba tch cultures to study the effect of osmotic stress and different feed rates on the growth kinetics. An unstructured model based on the linea r equation for substrate consumption provided an adequate description of the bacterial growth during the first phase of biomass production ( 20 h), except for cultures exposed to osmotic stress by the addition o f 0.5 M NaCl. The addition of salt to the culture media had a large ef fect on the energetics, that could not simply be described in terms of an increased maintenance requirement. In the later phase of growth, a n extensive decline in viability for all cultures was observed. Coinci dentally, the specific sugar uptake rate approached a lower limit. It is concluded that the total obtainable biomass in a fed batch culture is strongly affected by the magnitudes of the substrate feed rate and the ionic strength of the culture medium.