A second chromosomal copy of the catA gene endows Pseudomonas putida mt-2 with an enzymatic safety valve for excess of catechol

Pseudomonas putida mt-2 harbours two different routes for catabolism of catechol, namely one meta pathway encoded by the xyl genes of the TOL plasmid pWW0 and one ortho pathway determined by the chromosomal ben and cat genes. P. putida mt-2 has a second chromosomal copy of the catA gene (named catA2) located downstream of the ben operon that encodes an additional catechol-1,2-dioxygenase. The metabolic and regulatory phenotypes of strains lacking one enzyme, the other and both of them in cells with and without the TOL plasmid were evaluated. The data consistently indicated that induction of the ortho pathway by benzoate plasmid-less strain P. putida KT2440 led to catechol surplus, the toxicity of which at high concentrations being counteracted by CatA2. Cells carrying pWW0 but lacking catA2 experienced both a rapid loss of the plasmid when grown on benzoate (a substrate of the lower pathway) and a slowdown of their growth rate when cultured with benzylalcohol (a substrate converted to benzoate by the upper pathway). These data reveal the role of CatA2 as a type of metabolic safety valve for excess catechol that alleviates the metabolic conflict generated by simultaneous expression of the meta and ortho pathways, thereby facilitating their co-existence.