Isolation and characterisation of the entomopathogenic bacterium, Photorhabdus temperata producing a heat stable insecticidal toxin

Abstract

Entomopathogenic nematodes symbiotically associated with Photorhabdus spp. invade the larvae of susceptible insects and Photorhabdus bacteria are released into the insect hemolymph, which produce toxins and kill the insect larvae. In this study, five symbiotic bacteria isolates from soil nematodes, Heterorhabditis spp., have been reported. The bacteria were screened for insecticidal toxicity against larvae of Galleria mellonella. All were identified as different strains of Photorhabdus temperata via 16 s rDNA sequencing. The insecticidal activity was highest after 3-4 days of pure culture and the level of toxicity was higher in culture supernatant than in the cell pellet. The heat stability of the insecticidal activity was tested by heat treatments for 30 min at the range of 25°C to 100°C. Out of all isolated strains, P. temperata strains J4 and J5 produced heat-stable toxins. The supernatants extracted from the culture of these strains preserved up to 95% of insecticidal activity after heat treatment for 30 min at 80°C. The insecticidal activities of culture supernatants of all the selected strains were mostly maintained after proteinase K treatment. Based upon these findings, it can be inferred that the insecticidal toxins produced by Photorhabdus spp. were not pure protein substances.

Exploring the Insect Control and Plant Growth Promotion Potentials of Endophytes Isolated From Calotropis procera Present in Jeddah KSA

“…14,15 Application of CE exhibited a high level of insecticidal activity against G. mellonella larvae whilst the toxin was highly heat stable and proteinase-K stable. The results were supported by the findings of Jang et al 16 and Salvadori et al 17 deducing that the extracellular metabolites produced by entomopathogenic bacteria exclusively cause toxicity against a diverse group of insects. The stability of the toxin against heat and proteinase-K refers to its nonproteinous nature.…”

Synergistic Insecticidal Effect of Photorhabdus luminescens and Bacillus thuringiensis against Fall Armyworm (Spodoptera frugiperda)

“…A similar situation was observed with extracts from Photorhabdus temperata J4 and J5, where culture supernatants retained 95% of their insecticidal activity after 30 min of heat treatment at 80 • C, demonstrating their heat stability. Meanwhile, treatment with proteinase K did not change the insecticidal activity of the culture supernatants from all screened strains [71]. The above information shows that Photorhabdus can produce various metabolites with insecticidal and antimicrobial properties that possess heat stability and UV resistance, highlighting its potential as a novel microbial formulation.…”

Isolation and identification of entomopathogenic nematodes and their symbiotic bacteria from Kurdistan province in Iran

“…Isolation and identification of symbiotic bacteria of different EPNs were performed through several studies that identified different species including P. luminescens subsp. lumondii, P. temperate, X. bovienii, X. budapestensis, X. nematophila, X. poinarii (Iraki et al, 2000;Hazir et al, 2004;Bussaman et al, 2009;Agazadeh, et al, 2010;Jang et al, 2011;Karimi et al, 2011). The aims of this study were to: a: identify the entomopathogenic nematodes by morphological, morphometric and molecular data, b: find and introduce frequent native EPN species in Kurdistan province, c: characterize the symbiotic bacteria associated with EPNs based on biochemical and molecular approaches.…”