INVOLVEMENT OF CHROMOSOMALLY-ENCODED GENES IN MALATHION UTILIZATION BY PSEUDOMONAS AERUGINOSA AA112 ALY E. ABO-AMER Department of Botany, Division of Microbiology, Faculty of Science, Sohag University, Sohag, Egypt (Received: 14 January 2007; accepted: 7 March 2007) Malathion is an organophosphate insecticide that has been widely used for both domestic and commercial agricultural purposes. However, malathion has the po- tential to produce toxic effects in mammalian systems. In this study, Pseudomonas aeruginosa AA112 which was isolated from soil using enrichment technique could utilize the malathion as a sole carbon source and a source of energy. Pseudomonas aeruginosa AA112 was able to grow in MSMPY medium containing 42.75 mg/ml malathion. However, the optimum concentration of malathion which supported the maximum bacterial growth was found to be 22. 8 mg/ml. Malathion was used as an ini- tial source of energy and carbon when it was found without additional carbon sources (in MSM medium) while it was utilized as second source of energy and carbon in a nu- trient-supplemented medium (in MSMPY medium). Moreover, lead acetate test indi- cated that malathion was first attacked at a sulphur site 1–2 hours after the start of incu- bation. TLC and IR analysis indicated that malathion was completely degraded into di- ethyl succinate, hydrogen sulphide and phosphates. Therefore a malathion degrada- tion pathway was proporsed. The degradation of malathion is attributed to the genes located on the chromosome and at least three proteins of high molecular size might be involved in malathion utilization. Bacteria able to use malathion as a food source or metabolize its residues in the environment to inactive, less toxic, and harmless com- pounds, could be used in bioremediation of an environmental pollution caused by the pesticide. Keywords: Pseudomonas aeruginosa, biodegradation of malathion, plasmid, chromosome, SDS-PAGE 1217-8950/$20.00 © 2007 Akadémiai Kiadó, Budapest Acta Microbiologica et Immunologica Hungarica, 54 (3), pp. 261–277 (2007) DOI: 10.1556/AMicr.54.2007.3.3 Phone: 0020934609346; Mobile: 002 0103823361; Fax: 0020934601159; E-mail: abo-amer@lycos.com