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Appl Environ Microbiol, March 1998, p. 914-921, Vol. 64, No. 3
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Biochemical and Genetic Characterization of an Extracellular Protease from Pseudomonas fluorescens CY091

Ching-Hsing Liao* and Daniel E. McCallusdagger

Eastern Regional Research Center, Agricultural Research Service, USDA, Wyndmoor, Pennsylvania 19038

Received 10 September 1997/Accepted 17 December 1997

Pseudomonas fluorescens CY091 cultures produce an extracellular protease with an estimated molecular mass of 50 kDa. Production of this enzyme (designated AprX) was observed in media containing CaCl2 or SrCl2 but not in media containing ZnCl2, MgCl2, or MnCl2. The requirement of Ca2+ (or Sr2+) for enzyme production was concentration dependent, and the optimal concentration for production was determined to be 0.35 mM. Following ammonium sulfate precipitation and ion-exchange chromatography, the AprX in the culture supernatant was purified to near electrophoretic homogeneity. Over 20% of the enzyme activity was retained in the AprX sample which had been heated in boiling water for 10 min, indicating that the enzyme is highly resistant to heat inactivation. The enzyme activity was almost completely inhibited in the presence of 1 mM 1,10-phenanthroline, but only 30% of the activity was inhibited in the presence of 1 mM EGTA. The gene encoding AprX was cloned from the genome of P. fluorescens CY091 by isolating cosmid clones capable of restoring the protease production in a nonproteolytic mutant of strain CY091. The genomic region of strain CY091 containing the aprX gene was located within a 7.3-kb DNA fragment. Analysis of the complete nucleotide sequence of this 7.3-kb fragment revealed the presence of a cluster of genes required for the production of extracellular AprX in P. fluorescens and Escherichia coli. The AprX protein showed 50 to 60% identity in amino acid sequence to the related proteases produced by Pseudomonas aeruginosa and Erwinia chrysanthemi. Two conserved sequence domains possibly associated with Ca2+ and Zn2+ binding were identified. Immediately adjacent to the aprX structural gene, a gene (inh) encoding a putative protease inhibitor and three genes (aprD, aprE, and aprF), possibly required for the transport of AprX, were also identified. The organization of the gene cluster involved in the synthesis and secretion of AprX in P. fluorescens CY091 appears to be somewhat different from that previously demonstrated in P. aeruginosa and E. chrysanthemi.

* Corresponding author. Mailing address: Eastern Regional Research Center, USDA Agricultural Research Service, Wyndmoor, PA 19038. Phone: (215) 233-6471. Fax: (215) 233-6406. E-mail: cliao{at}arserrc.gov.

dagger Present address: Apollon Inc., Malvern, PA 19355-1423.




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