Mathematical analysis of catabolic function loss in a population of Pseudomonas putida mt-2 during non-limited growth on benzoate.

Pseudomonas putida mt-2, harbouring the TOL plasmid PWW0, was grown continuously on benzoate in a phauxostat at a non-limited rate. The gradual decrease in the population carrying the complete TOL plasmid was caused predominantly by a growth-rate advantage of spontaneous mutants carrying a partially deleted plasmid (TOL- cells). The growth-rate difference (v) was quantified both by measuring the increase in the dilution rate (from 0.68 to 0.79 h-1; v = 0.11 h-1) and by mathematical analysis of the ingrowth of TOL- cells (v = 0.12 h-1). The latter procedure also established that the segregation rate was of the order of magnitude 10(-5) h-1. Similar values for the growth-rate advantage and the segregation rate were found when both benzoate and succinate were present in non-limiting concentrations. It is suggested that the growth-rate disadvantage of the wild-type strain is caused by inhibitory effects of an intermediate in the degradation of benzoate via the plasmid-encoded meta-pathway.