Metabolic responses of microorganisms growing on inhibitory substrates in nonsteady state culture

The dynamics of metabolic activity of Pseudomonas putida cultured on phenol in a nonsteady state, resulting from simultaneous step increases (or decreases) in dilution rate and feed phenol concentration, were studied. Metabolic activity was determined by the uptake rate, defined as the mass of phenol degraded by a unit mass of bacteria in unit time. A minimum duration of nonsteady state was necessary to induce the metabolic pathway. The induction time for Pseudomonas putida cultured on phenol was approximately 30 min, irrespective of the type of disturbance applied. The Monod-Haldane equation was applied to fit the experimental values of uptake rate and the best kinetic parameters were calculated by the nonlinear least squares technique. Values of the kinetic parameters differed both for each parameter and type of disturbance investigated. For simultaneous step increases in dilution rate and feed phenol concentration, the value of u_m in the transient state first increased monotonically approximately four times and then decreased monotonically to the new steady state value after three residence times. Values of K_s and K_i attained those at the new steady state after three residence times, the highest being approximately three times greater than those of the steady state prior to disturbance. For simultaneous step decreases in D and S_O, values of u_m, K_s and K_i reached those at the new steady state values after four residence times.