Microbial lipases today occupy a place of prominence among biocatalysts owing to their ability to catalyze a wide variety of reactions. Out of 14 bacterial isolates obtained from wastewater sample. The isolates were grown on a selective medium agar that contained tween 80 or olive oil as the only source of carbon for detection of lipase activity 6 exhibited lipase activity. Pseudomonas aeruginosa (Ps₅) was the maximum clear zone (22 mm) around the colony and was selected for physicochemical studies. It was found that maximum lipase activity was 37 U.ml^-1 in liquid medium. Various physicochemical parameters such as pH, temperature and effect of different medium composition were studied in order to determine the optimum conditions for lipase production. The lipase present in the broth was purified with ammonium sulphate precipitation and DEAE cellulose chromatography to obtain 4 folds pure enzymes. The enzyme activity of the P. aeruginosalipase was enhanced by Ca²⁺ and Mg²⁺ but strongly inhibited by heavy metals Zn²⁺, Cu²⁺and Mn²⁺.

Key words: Pseudomonas aeruginosa, lipase activity, purification, biomass, heavy metals.