Assessment of Yersinia entomophaga as a control agent of the diamondback moth Plutella xylostella

The construction and evaluation of secretory expression engineering bacteria for the trans-Cry3Aa-T-HasA fusion protein against the Monochamus alternatus vector

Pine wood nematode disease is currently the most deadly forest disease in China, and the Monochamus alternatus is its primary vector. Controlling the M. alternatus is crucial for managing pine wood nematode disease. This study, based on the selected HasA (pGHKW4) secretory expression vector, used electroporation to combine the genetically modified high-toxicity toxin Cry3Aa-T with the entomopathogenic bacterium Yersinia entomophaga isolated from the gut of the M. alternatus. The SDS-PAGE and Western blotting techniques were employed to confirm the toxin protein's secretion capability. The engineered bacteria's genetic stability and effectiveness in controlling M. alternatus were assessed for their insecticidal activity. The results of the SDS-PAGE and Western blotting analyses indicate that the HasA system effectively expresses toxin protein secretion, demonstrates certain genetic stability, and exhibits high insecticidal activity against M. alternatus. This study constructed a highly toxic entomopathogenic engineered bacterial strain against M. alternatus larvae, which holds significant implications for controlling M. alternatus, laying the foundation for subsequent research and application of this strain.

Antifeeding and Oviposition Deterrent Effect of Ludwigia spp. (Onagraceae) against Plutella xylostella (Lepidoptera: Plutellidae)

Plants produce a wide variety of bioactive compounds with insecticidal properties, such as secondary metabolites capable of interfering with the nutrition and reproduction of pest species such as Plutella xylostella. Thus, the objective of this study was to evaluate the effects of aqueous and ethanolic extracts of Ludwigia spp. (Onagraceae) on the feeding and oviposition of P. xylostella. Choice bioassays were performed using aqueous and ethanolic extracts. The aqueous extract of L. tomentosa resulted in an approximately 81% reduction in larval feeding compared to that in the control, with an antifeedant index (AI) of 52%. The aqueous and ethanolic extract of L. nervosa acted by stimulating larval feeding. The oviposition was significantly reduced in the kale leaves treated with aqueous and ethanolic extracts of Ludwigia spp. The aqueous extracts promoted an average 90% reduction in oviposition when compared to that in the control, and an oviposition deterrent index (ODI) above 61% was classified as an oviposition deterrent. In addition, ethanolic extracts affected 81% of oviposition, with an ODI above 41%. Bioassays should be performed to clarify the use of aqueous and ethanolic extracts of L. nervosa as they acted as phagostimulants in the feeding tests and as deterrents in the oviposition tests. The phenolic compounds-flavonoids, condensed tannins, and alkaloids-were more abundant in L. nervosa, L. tomentosa, L. sericea, and L. longifolia. The extracts of L. longifolia and L. tomentosa showed the best results, interfering with the host choice for feeding and oviposition in P. xylostella and representing an alternative for the control of diamondback moths.

In vivo transcriptome analysis provides insights into host-dependent expression of virulence factors by Yersinia entomophaga MH96, during infection of Galleria mellonella

The function of microbes can be inferred from knowledge of genes specifically expressed in natural environments. Here, we report the in vivo transcriptome of the entomopathogenic bacterium Yersinia entomophaga MH96, captured during initial, septicemic, and pre-cadaveric stages of intrahemocoelic infection in Galleria mellonella. A total of 1285 genes were significantly upregulated by MH96 during infection; 829 genes responded to in vivo conditions during at least one stage of infection, 289 responded during two stages of infection, and 167 transcripts responded throughout all three stages of infection compared to in vitro conditions at equivalent cell densities. Genes upregulated during the earliest infection stage included components of the insecticidal toxin complex Yen-TC (chi1, chi2, and yenC1), genes for rearrangement hotspot element containing protein yenC3, cytolethal distending toxin cdtAB, and vegetative insecticidal toxin vip2. Genes more highly expressed throughout the infection cycle included the putative heat-stable enterotoxin yenT and three adhesins (usher-chaperone fimbria, filamentous hemagglutinin, and an AidA-like secreted adhesin). Clustering and functional enrichment of gene expression data also revealed expression of genes encoding type III and VI secretion system-associated effectors. Together these data provide insight into the pathobiology of MH96 and serve as an important resource supporting efforts to identify novel insecticidal agents.

Assessment of toxicity and persistence of Yersinia entomophaga and its Yen-Tc associated toxin

BACKGROUND

The insect-pathogenic bacterium Yersinia entomophaga MH96 is currently under development as a microbial pesticide active against various pasture and crop pests such as the diamondback moth Plutella xylostella and the cotton bollworm Helicoverpa armigeria. To enable nonrestricted field trials of Y. entomophaga MH96, information on the persistence and nontarget effects of the bacterium and its Yen-Tc proteinaceous toxin are required.

RESULTS

The Y. entomophaga Yen-Tc associated toxin was found to have limited persistence on foliage and is inactivated by UV light. The Yen-Tc was rapidly degraded in ovine or bovine rumen fluid or the intestinal fluid of H. armigera. In H. armigera an intestinal protein of >50 kDa was found to cleave the Yen-Tc bond. Assessment of Y. entomophaga persistence on foliage and in soil found that after 42 days the bacterium could not be detected in soil at 20% soil moisture content but persisted for 72 days at 30-40% soil moisture. Nontarget effects of Y. entomophaga towards earthworms found that the bacterium afforded no adverse effects on worm growth or behavior. A summary of historic Yen-Tc and Y. entomophaga persistence and toxicity data is presented.

CONCLUSION

The bacterium Y. entomophaga and its Yen-Tc associated toxin have limited persistence in the environment, with the Yen-Tc being susceptible to UV inactivation and proteolytic degradation, and the bacterium persisting longer in soil of a high moisture content. © 2020 Society of Chemical Industry.