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Published on: January 12, 2017
A metalloprotease secreted by the insect pathogen Photorhabdus luminescens induces melanization
Kiara G Held1, Christopher N LaRock, David A D'Argenio
1Department of Microbiology, University of Washington, Box 357242, Seattle, WA 98195, USA.
Abstract:
Photorhabdus luminescens is a gram-negative insect pathogen that enters the hemocoel of infected hosts and produces a number of secreted proteins that promote colonization and subsequent death of the insect. In initial studies to determine the exact role of individual secreted proteins in insect pathogenesis, concentrated culture supernatants from various P. luminescens strains were injected into the tobacco hornworm Manduca sexta. Culture supernatants from P. luminescens TT01, the genome-sequenced strain, stimulated a rapid melanization reaction in M. sexta. Comparison of the profiles of secreted proteins from the various Photorhabdus strains revealed a single protein of approximately 37 kDa that was significantly overrepresented in the TT01 culture supernatant. This protein was purified by DEAE ion-exchange and Superdex 75 gel filtration chromatography and identified by matrix-assisted laser desorption ionization-time of flight analysis as the product of the TT01 gene plu1382 (NCBI accession number NC_005126); we refer to it here as PrtS. PrtS is a member of the M4 metalloprotease family. Injection of PrtS into larvae of M. sexta and Galleria mellonella and into adult Drosophila melanogaster and D. melanogaster melanization mutants (Bc) confirmed that the purified protein induced the melanization reaction. The prtS gene was transcribed by P. luminescens injected into M. sexta before death of the insect, suggesting that the protein was produced during infection. The exact function of this protease during infection is not clear. The bacteria might survive inside the insect despite the melanization process, or it might be that the bacterium is specifically activating melanization in an attempt to circumvent this innate immune response.
Insights
Photorhabdus luminescens secretes a metalloprotease, PrtS, that triggers insect melanization. This response may help the bacteria evade or manipulate the insect
Area of Science:
- Insect pathology
- Bacterial pathogenesis
- Protease function
Background:
- Photorhabdus luminescens is a Gram-negative insect pathogen.
- Secreted proteins aid in insect colonization and host death.
Purpose of the Study:
- To identify secreted proteins involved in insect pathogenesis.
- To determine the role of specific P. luminescens proteins in host immune responses.
Main Methods:
- Injection of bacterial culture supernatants and purified proteins into insect models (Manduca sexta, Galleria mellonella, Drosophila melanogaster).
- Protein purification using ion-exchange and gel filtration chromatography.
- Protein identification via mass spectrometry.
- Gene transcription analysis.
Main Results:
- Culture supernatants from P. luminescens TT01 induced melanization in M. sexta.
- A 37 kDa metalloprotease, PrtS (product of plu1382), was identified as the inducer.
- PrtS injection triggered melanization in multiple insect species and mutants.
- prtS gene transcription was detected during infection.
Conclusions:
- PrtS is a secreted metalloprotease from P. luminescens that induces insect melanization.
- The function of PrtS in pathogenesis may involve immune evasion or manipulation.
- Further research is needed to clarify PrtS's precise role during P. luminescens infection.
