Screening of nonfilamentous bacteria for production of cutin-degrading enzymes.

Two hundred thirty-two nonfilamentous bacterial strains, including saprophytes, plant pathogens, and opportunistic plant and human pathogens, were screened for the ability to produce cutinases (cutin-degrading esterases). Initially, esterase activity of culture filtrates of strains grown in nutrient broth-yeast extract medium supplemented with 0.4% apple or tomato cutin was determined by a spectrophotometric assay utilizing the model substrate p-nitrophenyl butyrate. The culture filtrates of the 10 Pseudomonas aeruginosa strains tested exhibited the highest esterase activity, with values of >500 nmol/min/ml. Of these 10 strains, 3 (K799, 1499A, and DAR41352) demonstrated significant induction (10-fold or above) of esterase activity by addition of cutin to nutrient broth-yeast extract medium. The ability of culture filtrates of the three strains to cause release of apple cutin monomers was confirmed by a novel high-performance liquid chromatography technique. Monomer identification was confirmed by gas chromatography-mass spectroscopy analyses. Addition of the nonionic detergent n-octylglucoside stimulated cutinase activity of culture filtrates from strains K799 and DAR41352, but not that of filtrates from strain 1499A. Time course studies in nutrient broth-yeast extract medium supplemented with apple cutin indicated maximal levels of cutinase in the culture fluids after cultures entered stationary phase. Incubation temperatures below the optimal temperature for growth (37 degrees C) led to maximal production of cutinase.