Bacillus cereus and Pseudomonas aeruginosa were isolated from the effluent of the Kaduna refining and petrochemical company, using standard methods. These were UV-irradiated for 30mins and thereafter subjected to nitrous acid treatment. Determination of essential amino acids
required by both parents and mutants for growth showed that the mutant of Pseudomonas aeruginosa did not require valine and histidine for growth. The mutational treatments resulted in a sense mutation with beneficial effects of increased petroleum degradation. The amino acids
requirement for growth could thus be used as a genetic marker for organisms that are subjected to mutational treatments.