Interactions between Bacillus thuringiensis subsp. kurstaki HD-1 and midgut bacteria in larvae of gypsy moth and spruce budworm

Midgut microbiota and host immunocompetence underlieBacillus thuringiensiskilling mechanism

“…This approach allowed us to study, in a realistically physiological context characterized by an unaltered midgut microbiota, the role of the enteric flora in the induction of lethal septicemia following B. thuringiensis toxin-induced damage. This is a controversial hypothesis that has been widely debated over the last decade (22,23,27,28,40).…”

“…A heated debate on the B. thuringiensis killing mechanism started almost a decade ago, and a consensus has not yet been reached. Indeed, divergent opinions persist on the role played by the microbiota residing in the midgut of lepidopteran hosts and the septicemia it may cause after toxin-induced disruption of the lining epithelium (22)(23)(24)(25)(26)(27)(28)(29)(30)(31). Whether the gut paralysis and associated feeding cessation observed in larvae exposed to Cry pore-forming toxins or the septicemia induced by bacterial proliferation in the insect body cavity is the major factor contributing to eventual death remains to be resolved (5,32) Significance Bacillus thuringiensis and its toxins are widely used for insect control.…”

“…To circumvent the problems associated with the manipulation of the midgut microbiota with antibiotics (22)(23)(24)(25)(27)(28)(29)(30)(31) or of the immune response with immunosuppressive molecules (26,34), both of which have unpredictable multiple effects, we performed selective RNAi-mediated silencing of an immune gene (102 Sl, 102 Spodoptera littoralis), recently identified in Spodoptera littoralis (35). This gene is highly expressed in the immune cells circulating in the hemolymph (i.e., hemocytes) and modulates their incorporation in multilayered capsules formed around foreign intruders entering the body cavity (i.e., the hemocoel) (35).…”

Host and symbiont jointly control gut microbiota during complete metamorphosis

“…Here we exploit an ancient [19], facultative and prevalent [20][21][22][23][24][25][26] symbiosis between Lepidoptera and enterococci to reconcile these approaches by studying the role of host immunity and bacterial competition during metamorphosis within a single system. The gut microbiota of Lepidoptera is limited to a handful of bacterial species that varies with habitat and diet but often is dominated by enterococci that persist through metamorphosis [12].…”

More wrinkles to Bt susceptibility

“…[10][11][12] This model launched a heated debate in the field, as others showed that while elimination of the gut microbiota by antibiotic feeding could reduce susceptibility, the mechanism of gut microbiota suppression was due to a direct effect of antibiotics on the Bt toxin. [13][14][15] More recently, a number of studies, including this issues' paper and previous work from Dubovskiy and colleagues 16 have described impacts of Bt on the microbiome and contributions of microbiota and the immune response to host susceptibility. Similarly, a recent paper from Caccia et al 17 reported on a related mechanism of Bt-induced lethality in which septicemia caused by the midgut bacteria of another lepidopteran host, Spodoptera littoralis, was more pronounced in immunocompromised hosts following RNAi knockdown of a specific immune gene.…”