Expression of prtA from Photorhabdus luminescens in Bacillus thuringiensis enhances mortality in lepidopteran larvae by sub-cutaneous but not oral infection

Abstract

The prtA gene from Photorhabdus luminescens encodes the virulence factor Protease A. When P. luminescens is injected into the hemocoel of insects by entomopathogenic nematodes, PrtA is a key component of pathogenicity thought to help degrade the immune system. The prtA gene was cloned and introduced on a plasmid into Bacillus thuringiensis. PrtA was shown to be actively expressed in vitro by cleavage of a specific Dabcyl-Edans heptapeptide substrate. There was no difference in the speed or level of mortality when spores and δ-endotoxins crystals of the transformed strain were fed to larvae of Pieris brassicae, as compared to the wild-type strain. When vegetative cells were injected into the hemocoel of larvae of Galleriamellonella, however, there was a significant increase in the rate and level of mortality over the wild type. The yield of B. thuringiensis per cadaver was a hundred-fold greater in the PrtA-secreting strain. The increased pathogenicity from intrahemocoelic infection may have been due to a greater ability to overcome the immune response of G. mellonella while other factors such as resident gut bacteria may have negated this advantage after oral dosage.

Larvicidal activities of indigenousBacillus thuringiensisisolates and nematode symbiotic bacterial toxins against the mosquito vector Culex pipiens(Diptera: Culicidae)

“…Further evidence has been provided by Vani and Lalithambika (2014) who recorded 93.32% mortality for the 3 rd larval instar of Anopheles gambiae when he used 100ng/ml of the extracellular proteins (from 20–97 KDa) of the outer membrane of Xenorhabdus sp bacteria isolated from Steinernema sp nematode. Moreover, Bishop (2014) has successfully cloned and introduced the prtA gene (encodes the protease A virulence factor) from Ph. luminescens into Bacillus thuringiensis which enhanced the mortality in larvae of the lepidopteran moth, Pieris brassicae and Galleria mellonella when taken orally and injected into the hemocoel respectively compared to the wild type of B. thuringiensis .…”

From Insect to Man: Photorhabdus Sheds Light on the Emergence of Human Pathogenicity

“…However, it has been suggested that PrtA is used to generate the amino acids required for nutrition during bioconversion of the insect cadaver, as it is only detectable 24 h after infection [ 63 ]. In a recent study, the heterologous expression of this PrtA in Bacillus thuringinesis increases both the virulence and final bacterial yield in insect blood [ 64 ] suggesting a potential additional role in immune evasion. This suggestion is also supported by the finding that PrtA can cleave six M .…”

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

“…In the case of histopathological sections, in both S. frugiperda and Pl. xylostella, pathological features of both midgut epithelial cell disruption (a typical symptom caused by Bt) and cell vacuolation with increased vesicle formation (a typical symptom caused by Pl) were observed in the mixed treatments of Pl and Bt, confirming the occurrence of a synergistic effect [19,23,24,39,[41][42][43][44].…”