Summary: Steady-state chemostat cultures of growing on a carbon-limited medium were challenged with pulses of carbon sources, and the resultant changes in dissolved oxygen tension were shown to reflect changes in respiration rate. These changes were used to study the kinetics of induction of citrate-oxidizing capacity, which is most probably limited by citrate permease, and the return to the preinduced state. Previously unexposed cells showed a lag phase, the duration of which decreased with increasing growth rate, with a minimum of 10min, followed by an induction phase of linear increase of citrate oxidation rate which continued as long as citrate was present. The rate of increase in activity, which can be equated to the rate of induction of citrate permease, was independent of citrate concentration but increased with growth rate. Previously exposed cells showed no lag and some residual activity before further induction. The kinetics of return to the preinduced state were unusual in that activity was short-lived with a half-life of 16 to 23 min while the lag took over 8 h to re-establish. The rate of decay of activity decreased with increasing growth rate.


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