New cell growth pattern on mixed substrates and substrate utilization in cometabolic transformation of 4-chlorophenol

The effect of varying phenol concentration on cometabolic transformation of 4-chlorophenol (4-CP) by Pseudomonas putida in the presence of a conventional carbon source, sodium glutamate (SG), was investigated. When SG was provided as the sole growth substrate, both the extent and efficiency of 4-CP transformation were severely reduced compared with that when phenol was the sole growth substrate. By supplementing phenol to the mixture of SG and 4-CP, both the rate and extent of cometabolic transformation of 4-CP were greatly enhanced. Nevertheless, the presence of SG attenuated the toxicity of 4-CP on cell growth and minimized the amount of phenol required for the complete transformation of 4-CP. A new cell growth pattern characterized by two exponential growth phases separated by an intermediate lag phase was observed in this cometabolism process. Cells preferentially utilized phenol in the first growth phase while SG was mainly utilized in the second growth phase. With increase of phenol concentration, however, it was found that an increasing amount of SG was consumed concurrently with phenol in the first growth phase and the length of the intermediate lag phase was found to decrease linearly with phenol concentration until only one growth phase was observed. Analysis of experimental results suggests that the disparity of the toxicity of 4-CP to phenol-oxidizing and SG-oxidizing enzyme activities is the cause of this new cell growth pattern.