Characterization of an Insecticidal Toxin and Pathogenicity of Pseudomonas taiwanensis against Insects

Abstract

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.

Defensive repertoire of Drosophila larvae in response to toxic fungi

“…Pathogens, including those that are opportunistic, have been shown to manipulate immune responses of their hosts by different means (Rieber et al., ; Vallet‐Gely, Lemaitre, & Boccard, ), and secondary metabolites are suggested to be relevant agents (Chen et al., ; Vey, Matha, & Dumas, ; Vilcinskas, Matha, & Götz, ). While it remains speculative to invoke an active manipulation of larvae's responses by the fungus, these patterns might be indicative of an early but temporary impairment of insect classical detoxification countermeasures against the toxic secondary metabolites that fungi can produce.…”

A selective insecticidal protein from Pseudomonas mosselii for corn rootworm control

“…Monalysin, a b-pore-forming toxin from P. entomophila, showed lethal effects on Drosophila (Opota et al, 2011). P. taiwanensis, a broad-host-range entomopathogenic bacterium, exhibited insecticidal activity towards agricultural pests, and its large molecular weight multicomponent toxin complex (Tc) was found to play an essential role in the activity (Chen et al, 2014). Recently, novel insecticidal proteins with activity against key crop insect pests have been identified from non-Bt microbes.…”

A look into the toolbox of multi‐talents: insect pathogenicity determinants of plant‐beneficial pseudomonads

“…Gut colonization in presence of the resident microbiota may require type VI secretion-mediated competition (Cianfanelli et al, 2016;P echy-Tarr et al, unpublished). Potent insecticidal activity occurs also in certain other environmental pseudomonads, notably within the Pseudomonas putida (Opota et al, 2011;Chen et al, 2014), Pseudomonas syringae (Nadarasah and Stavrinides, 2011) and Pseudomonas aeruginosa (Kupferschmied et al, 2013) groups, and it may be rewarding to compare strategies and toolboxes they use. There are still numerous questions for future work.…”

“…by exploiting insects as containers to persist, multiply, and travel (or feed on) as it has been observed for various plant pathogens. Potent insecticidal activity occurs also in certain other environmental pseudomonads, notably within the Pseudomonas putida (Opota et al, 2011;Chen et al, 2014), Pseudomonas syringae (Nadarasah and Stavrinides, 2011) and Pseudomonas aeruginosa (Kupferschmied et al, 2013) groups, and it may be rewarding to compare strategies and toolboxes they use. In a longer-term perspective, specific strains of these competitive plant colonizers displaying activities both against plant pathogens and against herbivorous insects could be developed for biotechnological applications such as control of agricultural pests.…”