A NEW EXPERIMENTAL-METHOD TO REVEAL DENSITY-DEPENDENT CHEMICAL FACTORS INVOLVED IN MICROBIAL-POPULATION GROWTH-CONTROL

Experiments based on an earlier developed theory with a culture of Esc herichia coli 0-124 were undertaken to determine the feedback strength (FBS) in growth control. FBS is defined as the change in growth accel eration brought about by a discontinuous reduction in microbial concen tration under conditions of constant chemical composition of the mediu m, and is an over-all measure of the regulatory influence of all chemi cal factors dependent on biomass concentration. FBS was determined for batch cultivation with glucose. In various growth phases the culture was diluted by its own filtrate and then the change in growth accelera tion as compared to the control was measured. FBS was reliably differe nt from zero at the end of the exponential phase and in the phase of d ecelerated growth and was of the order of -20 to -200 (h.g/liter)(-1). The feedback component due to glucose alone was estimated using the o btained relation between specific growth rate and glucose concentratio n (mu(max) = 0.55 +/- 0.05 h(-1), K-s = 2.5 +/- 0.7 mg/liter). The glu cose-dependent regulatory contribution to FBS was found to be as low a s 0.5 to 40%, which suggests the presence of other growth control fact ors. Upon accuracy improvements, this method may develop into an accep ted microbiological tool for identifying major density-dependent facto rs involved in microbial growth control.