A procedure for identifying and profiling cutinolytic esterases was developed by combining traditional plate screen assays with an automated robotic system. In the first phase, the micro-organisms were screened on agar plates with cutin or the model substrate polycaprolactone as the sole carbon sources. In the second phase, p-nitrophenyl esters of fatty acids were used as the substrates in an automated activity assay of liquid culture media. The variables used were pH and the carbon chain length of the fatty acid moiety of the p-nitrophenyl substrate. Finally, 3H-labelled cutin was used as a specific substrate to verify the positive hits and to validate the screening procedure. With pH as the variable in the automatic screen, esterase production of cutinase positive strains typically proceeded in two stages: first an esterase with neutral activity optimum was produced, after which a strong esterolytic response in the alkaline range was detected. With carbon chain length of the fatty acid as the variable best correlation with cutinase production was obtained with strains showing a high ratio of activities towards p-nitrophenyl-butyrate and p-nitrophenyl-palmitate.
- high throughput