Characterization of an insecticidal toxin and pathogenicity of Pseudomonas taiwanensis against insects

• Published in: PLoS pathogens Vol. 10; no. 8; p. e1004288
• Main Authors: Chen, Wen-Jen, Hsieh, Feng-Chia, Hsu, Fu-Chiun, Tasy, Yi-Fang, Liu, Je-Ruei, Shih, Ming-Che
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.08.2014; Public Library of Science (PLoS)
• Subjects: Agricultural pests; Animals; Apoptosis; Bacteria; Bacterial Toxins - genetics; Bacterial Toxins - metabolism; Biology and Life Sciences; Blotting, Western; Control; Distribution; Flow Cytometry; Gene Knockout Techniques; Genes; Immunohistochemistry; Infections; Insecta - parasitology; Insecticides; Insects; Laboratory animals; Mortality; Moths - parasitology; Pathogenesis; Pest Control, Biological - methods; Proteins; Pseudomonas; Pseudomonas - genetics; Pseudomonas - metabolism; Pseudomonas - pathogenicity; Real-Time Polymerase Chain Reaction; Virulence; Taiwan
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1004288

Pseudomonas taiwanensis is a broad-host-range entomopathogenic bacterium that exhibits insecticidal activity toward agricultural pests Plutella xylostella, Spodoptera exigua, Spodoptera litura, Trichoplusia ni and Drosophila melanogaster. Oral infection with different concentrations (OD = 0.5 to 2) of wild-type P. taiwanensis resulted in insect mortality rates that were not significantly different (92.7%, 96.4% and 94.5%). The TccC protein, a component of the toxin complex (Tc), plays an essential role in the insecticidal activity of P. taiwanensis. The ΔtccC mutant strain of P. taiwanensis, which has a knockout mutation in the tccC gene, only induced 42.2% mortality in P. xylostella, even at a high bacterial dose (OD = 2.0). TccC protein was cleaved into two fragments, an N-terminal fragment containing an Rhs-like domain and a C-terminal fragment containing a Glt symporter domain and a TraT domain, which might contribute to antioxidative stress activity and defense against macrophagosis, respectively. Interestingly, the primary structure of the C-terminal region of TccC in P. taiwanensis is unique among pathogens. Membrane localization of the C-terminal fragment of TccC was proven by flow cytometry. Sonicated pellets of P. taiwanensis ΔtccC strain had lower toxicity against the Sf9 insect cell line and P. xylostella larvae than the wild type. We also found that infection of Sf9 and LD652Y-5d cell lines with P. taiwanensis induced apoptotic cell death. Further, natural oral infection by P. taiwanensis triggered expression of host programmed cell death-related genes JNK-2 and caspase-3.