Biodegradation kinetics of 4-chlorophenol, an inhibitory co-metabolite

Kinetic experiments were performed with batch reactors containing a pure culture of Pseudomonas putida PpG4 and 4-chlorophenol as the only organic substrate present. 4-Chlorophenol behaved as a cometabolite because its transformation, possible only with cells previously grown on phenol, did not yield any increase in cell mass. Exponential decay described the time-dependent biomass concentrations reasonably well; the estimated decay coefficient was 0.013/h (0.3/day). The 4-chlorophenol-transformation rate was controlled by the 4-chlorophenol/biomass (I:X) ratio. For low I:X ratios, the system was uninhibited, complete 4-chlorophenol transformation was observed, and the 4-chlorophenol-transformation rate was proportional to the biomass-oxidation rate. The link in the rates was observed probably because the electrons consumed during the 4-chlorophenol transformation were produced by way of biomass oxidation. The constant of proportionality between the rates of 4-chlorophenol transformation and biomass decay corresponds to the cells shunting about 9% of the electrons provided by biomass oxidation to 4-chlorophenol transformation. For high I:X ratios, the system was inhibited by 4-chlorophenol itself, the initial 4-chlorophenol transformation was slow, it further slowed, and it rapidly reached a zero rate, leaving a significant fraction of the 4-chlorophenol untransformed.