Multiple stable states and hysteresis in continuous, oscillating cultures of budding yeast

The conditions that precede the onset of autonomous oscillations in continu ous yeast cultures were studied in three different types of experiments. It was found that the final state of the culture depended on the protocol use d to start up the reactor. Batch cultures, switched to continuous operation at different stages of the batch growth curve, all exhibited similar dynam ics-ethanol depletion followed by autonomous oscillations. Small perturbati ons of the distribution of states in the reactor, achieved by addition of e xternally grown cells, were able to quench the oscillatory dynamics, Reachi ng the desired operating point by slow dilution rate changes gave rise to d ifferent final states, two oscillatory states and one steady state, dependi ng on the rate of change in dilution rate. The multiplicity of stable state s at a single operating point is not explained by any current distributed m odel and points toward a segregated mechanism of these oscillations. (C) 20 01 John Wiley & Sons, Inc.