Immuno-physiological adaptations confer wax mothGalleria mellonellaresistance toBacillus thuringiensis

Abstract

Microevolutionary mechanisms of resistance to a bacterial pathogen were explored in a population of the Greater wax moth, Galleria mellonella, selected for an 8.8-fold increased resistance against the entomopathogenic bacterium Bacillus thuringiensis (Bt) compared with a non-selected (suspectible) line. Defense strategies of the resistant and susceptible insect lines were compared to uncover mechanisms underpinning resistance, and the possible cost of those survival strategies. In the uninfected state, resistant insects exhibited enhanced basal expression of genes related to regeneration and amelioration of Bt toxin activity in the midgut. In addition, these insects also exhibited elevated activity of genes linked to inflammation/stress management and immune defense in the fat body. Following oral infection with Bt, the expression of these genes was further elevated in the fat body and midgut of both lines and to a greater extent some of them in resistant line than the susceptible line. This gene expression analysis reveals a pattern of resistance mechanisms targeted to sites damaged by Bt with the insect placing greater emphasis on tissue repair as revealed by elevated expression of these genes in both the fat body and midgut epithelium. Unlike the susceptible insects, Bt infection significantly reduced the diversity and richness (abundance) of the gut microbiota in the resistant insects. These observations suggest that the resistant line not only has a more intact midgut but is secreting antimicrobial factors into the gut lumen which not only mitigate Bt activity but also affects the viability of other gut bacteria. Remarkably the resistant line employs multifactorial adaptations for resistance to Bt without any detected negative trade off since the insects exhibited higher fecundity.

Phenological asynchrony between host plant and gypsy moth reduces insect gut microbiota and susceptibility to Bacillus thuringiensis

“…The level of insect resistance to B. thuringiensis as well as to many other pathogens is determined by the status of its innate immunity (Dubovskiy et al., ; Ma, Sarjan, Preston, Asgari, & Schmidt, ). One of the main parameters mediating the outcome of insect–bacteria interactions is the prevalence of lysozyme and lower molecular weight antimicrobial peptides (AMPs) (Hwang & Kim, ; Johnston & Rolff, ).…”

More wrinkles to Bt susceptibility

“…5 In this issue of Virulence, the authors of the article "Immuno-physiological adaptations confer wax moth Galleria mellonella resistance to Bacillus thuringiensis" utilized an artificial selection experiment to identify traits that lead to Bt resistance, focusing on several characteristics previously implicated in toxin resistance. 6 Following selection for Bt resistance over 20 generations, Dubovskiy et al first measured the expression of 15 genes with roles in immune, stress, and inflammation responses in both the midgut (site of toxin binding) and the fat body, which is an important metabolic and homeostatic organ in the body cavity that produces many stress and immune effectors. Comparison between larvae from susceptible and resistant lines showed that resistant larvae had significantly higher expression levels of an inducible metalloprotease inhibitor, which inhibits proteases that contribute to Bt toxin activation, 2 growth factors in the midgut, and slightly elevated expression of additional immune and stress response genes.…”

Is there a transgenerational inheritance of host resistance against pathogens? Lessons from the Galleria mellonella-Bacillus thuringiensis interaction model

“…a higher fecundity) and a decrease in the diversity of the gut microbiota. 20 Change in epigenetic patterns in a Galleria resistant line after 30 generations of selection.…”

“…The understanding of the tolerance mechanisms of Galleria to Bt-Cry biocides has improved significantly thanks to the resistance evolution model in Galleria 20,9 There is now a need to explore in detail the relative importance on the selected resistance phenotype of Cry toxins and the other virulence factors expressed by Bt during infection. 15 Another important issue raised by this work is whether similar phenomena occur in insect pests, which are of high economical importance, such as Plutella xylostella.…”

“…In a pioneer study, Dubovskiy et al 20 developed an evolutionary model focused on the resistance of G. mellonella against Bt spore-Cry mixtures. After a long-term selection process for 20 generations, they obtained a resistant Galleria line, which was about 9-fold more resistant to the pathogen than the non-selected control.…”