This study focuses on capability of Pseudomonas pseudoalcaligenes C70 to degrade phenol and salicylate. These persistent and toxic aromatic compounds may reach to the environment as pollution from industries or as a result of oil pollution. Strain C70 has a great potential for the bioremediation of contaminated areas as it possesses two catechol meta pathways. To study the role of two key enzymes, catechol 2,3-dioxygenases (C23O), a mutant strain was constructed. Based on the conducted experiments it can be stated that the studied mutant strain C70∆pheB possessing only one C23O cannot function in the proper way on phenol – naphthalene route’s C23O is not able to replace phenol route C23O. Two copies of C23O in wt strain allow to grow on higher concentrations of contamination.