Isolation and optimization of thermophilic lipase producing bacteria from soil contaminated with used engines oil

Abstract

Thirty two of thermophilic bacterial isolates producing lipase were selectively isolated from soil samples contaminated with used engines oil using Tributyrin agar medium. The qualitative assay of lipase activity was done on Tributyrin agar plates by measuring diameter of the clear zone. The isolates 6T, 14T and 29T of the isolated strains exhibited a greater zone of clearance than the others, indicating higher lipase activity. Secondary screening for lipase production was done using liquid basal medium with 1% (w/v) olive oil and pH 7. Results from quantitative assay showed that 6T, 14T and 29T isolates appeared highest ability to produce lipase enzyme 4 U/ml, 10 U/ml and 7 U/mlrespectively. Therefore, the 14T isolate was selected and identified based on their morphological and physiological characteristics which was subsequently identified and designated as Bacillus licheniformis. The effect of incubation time, temperature and pH influencing lipase production from Bacillus licheniformis14T isolate was determine. Results showed that the maximal lipase production was 11 U\ml after 3 day of incubation at medium pH7 and temperature 50 0C.