Assessment of inhibition kinetics of the growth of strain P5 on pentachlorophenol under steady-state conditions in a nutristat.

A bacterium degrading pentachlorophenol (PCP) as the only source of carbon and energy was grown in a nutristat , i.e., a continuous culture with on-line measurement and control of the substrate concentration. We improved the PCP nutristat by incorporation of a personal computer with a proportional integral derivative (PID) algorithm for controlling the medium feed pump. The controlled value deviated from the average (set-point) value by 1% maximally. In the PCP nutristat (30 degrees C), the steady-state dilution rate, and hence, specific growth rate, showed a maximum value of 0.142 +/- 0.004 h-1 at set-point PCP concentrations between 37 and 168 microM. At PCP concentrations above 168 microM, the steady-state growth rate decreased because of inhibition. The growth yield coefficient was not seriously affected by the PCP concentration, suggesting that uncoupling was not the inhibitory mechanism. It was concluded that the PCP nutristat is very useful for establishing steady-state conditions that maintain growth-inhibitory PCP concentrations and high cell concentrations, conditions for which the chemostat is not suitable.