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Isolation and Preliminary Characterization of Extracellular Proteases Produced by Strains of Xylella fastidiosa from Grapevines. S. M. Fry, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; J.-S. Huang, and R. D. Milholland. professors, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 84:357-363. Accepted for publication 16 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-357.

Virulent and weakly virulent grape strains of Xylella fastidiosa grew well on PD3 amended with gelatin and produced zones of hydrolysis on this medium, indicating the presence of proteolytic activity. Proteases also were produced in PD3 broth and degraded gelatin, azocasein, and azocoll. Gelatin was the best substrate for the proteases. In addition to using the gelatin assay, native activity and sodium dodecyl sulfate activity gels aided in visualizing and monitoring protease activity. Strain P of X. fastidiosa produced at least two proteases, designated P1 and P2, of 54 and 50 kDa, respectively. Protease activity was most abundant in the 31–60% ammonium sulfate fractions. Protease production was positively correlated with bacterial growth in PD3 broth and reached a maximum near the stationary phase of bacterial growth. P2 became more and P1 became less predominant over time in PD3 broth. Protease activity was not diminished by temperatures up to 60 C and was optimal at 50 C and pH 9.0. P1 and P2 were similarly affected by pH and temperature.

Additional keywords: Pierce’s disease.