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Applied and Environmental Microbiology, July 2004, p. 3831-3838, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.3831-3838.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Purification and Characterization of Two Distinct Metalloproteases Secreted by the Entomopathogenic Bacterium Photorhabdus sp. Strain Az29

C. M. Cabral, A. Cherqui, A. Pereira, and N. Simões^*

CIRN and Departamento de Biologia, Universidade dos Açores, Azores, Portugal

Received 2 December 2003/ Accepted 14 March 2004

Photorhabdus sp. strain Az29 is symbiotic with an Azorean nematode of the genus Heterorhabditis in a complex that is highly virulent to insects even at low temperatures. The virulence of the bacteria is mainly attributed to toxins and bacterial enzymes secreted during parasitism. The bacteria secrete proteases during growth, with a peak at the end of the exponential growth phase. Protease secretion was higher in cultures growing at lower temperatures. At 10°C the activity was highest and remained constant for over 7 days, whereas at 23 and 28°C it showed a steady decrease. Two proteases, PrtA and PrtS, that are produced in the growth medium were purified by liquid chromatography. PrtA was inhibited by 1,10-phenantroline and by EDTA and had a molecular mass of 56 kDa and an optimal activity at pH 9 and 50°C. Sequences of three peptides of PrtA showed strong homologies with alkaline metalloproteases from Photorhabdus temperata K122 and Photorhabdus luminescens W14. Peptide PrtA-36 contained the residues characteristic of metzincins, known to be involved in bacterial virulence. In vitro, PrtA inhibited antibacterial factors of inoculated Lepidoptera and of cecropins A and B. PrtS had a molecular mass of 38 kDa and was inhibited by 1,10-phenanthroline but not by EDTA. Its activity ranged between 10 and 80°C and was optimal at pH 7 and 50°C. PrtS also destroyed insect antibacterial factors. Three fragments of PrtS showed homology with a putative metalloprotease of P. luminescens TTO1. Polyclonal antibody raised against PrtA did not recognize PrtS, showing they are distinct molecules.

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* Corresponding author. Mailing address: Departamento de Biologia, Universidade dos Açores, 9501-801 Ponta Delgada, Azores, Portugal. Phone: 351-296-650-119. Fax: 351-296-650-100. E-mail: simoes{at}notes.uac.pt.

Present address: Faculté des Sciences, Laboratoire de Biologie des Entomophages, Université de Picardie Jules Verne, Amiens 80039, France.

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Applied and Environmental Microbiology, July 2004, p. 3831-3838, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.3831-3838.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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