Prediction of critical cell growth behavior of Pseudomonas putida to maximize the cometabolism of 4-chlorophenol with phenol and sodium glutamate as carbon sources

In our study on cometabolism of 4-chlorophenol (4-cp) by Pseudomonas putida ATCC 49451 in the presence of phenol and a conventional carbon source, sodium glutamate (SG), a new biphasic cell growth pattern characterized by two exponential growth phases separated by an intermediate lag phase was observed. This biphasic growth pattern results from the toxicity disparity of 4-cp to phenol-degrading enzyme and SG-degrading enzyme activities. This paper presents further experimental study and model analysis to predict the occurrence of the biphasic growth pattern. Experimental results show that this growth pattern occurs at a high 4-cp concentration accompanied by a low phenol concentration and/or a high SG concentration. Using a set of growth kinetics equations developed earlier, which incorporates the cross-inhibition between the structurally dissimilar growth substrates (phenol and SG) and interactions between growth and non-growth substrates, as well as the toxicity of 4-cp, a criterion is proposed for predicting the occurrence of the biphasic growth pattern. These findings and model predictions not only help us to better understand the substrate interactions in the mixture and the toxicity of 4-cp, but they are also of practical significance in process control and design of a cometabolism system involving multiple substrates. For example, using the kinetics model, the ratio of phenol to 4-cp and the addition of SG to enhance cometabolism can be better defined to optimize the cometabolic treatment process.