Biosurfactants Induce Antimicrobial Peptide Production through the Activation of TmSpatzles in Tenebrio molitor

Abstract

Biosurfactant immunomodulatory activities in mammals, nematodes, and plants have been investigated. However, the immune activation property of biosurfactants in insects has not been reported. Therefore, here, we studied the defense response triggered by lipopeptides (fengycin and iturin A), glycolipids (rhamnolipid), and cyclic polypeptides (bacitracin) in the coleopteran insect, mealworm Tenebrio molitor. The in vitro antimicrobial activities against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and fungi (Candida albicans) were assessed by mixing these pathogens with the hemolymph of biosurfactant-immune-activated larvae. E. coli growth was remarkably inhibited by this hemolymph. The antimicrobial peptide (AMP) induction results also revealed that all biosurfactants tested induced several AMPs, exclusively in hemocytes. The survivability analysis of T. molitor larvae challenged by E. coli (106 CFU/µL) at 24 h post biosurfactant-immune activation showed that fengycin, iturin A, and rhamnopid significantly increased survivability against E. coli. Biosurfactant-induced TmSpatzles activation was also monitored, and the results showed that TmSpz3 and TmSpz-like were upregulated in the hemocytes of iturin A-injected larvae, while TmSpz4 and TmSpz6 were upregulated in the fat bodies of the fengycin-, iturin A-, and rhamnolipid-injected larvae. Overall, these results suggest that lipopeptide and glycolipid biosurfactants induce the expression of AMPs in T. molitor via the activation of spätzle genes, thereby increasing the survivability of T. molitor against E. coli.

Emerging Evidence on Tenebrio molitor Immunity: A Focus on Gene Expression Involved in Microbial Infection for Host-Pathogen Interaction Studies

“…Although it was expressed in all tissues and the whole body, the highest expression was observed in the intestine, fat bodies, and MTs 24 hours after microbial infection. Furthermore, in agreement with previous studies [ 99 , 100 ], Tm-Spz-like knockdown larvae exposed to E. coli exhibited significantly lower viability. These findings endorsed the downregulation of 11 encoding Gram-negative AMP genes (out of 15 genes tested).…”

“…After that, in 2020 the same authors reported the response of biosurfactants (bacitracin, fengycin, iturin A, and rhamnolipids) in modulating several T.molitor Spätzle, namely Spz3 (Genbank CAH1376064), Spz4 (Genbank MT075617), Spz6 (Genbank CAH1365756), and Spz-like (Genbank MZ708792) along with AMP expression [ 100 ]. In larvae inoculated with biosurfactants, the expression of AMPs through activation of Tm-Spz genes in hemocytes was observed.…”

“…Moreover, the biosurfactants’ effect on Spz-silenced larvae was investigated to confirm the protein involvement in the immune response induced by biosurfactants. Tm-Spz knockdown larvae were more susceptible to E. coli infection despite immuno-stimulation with biosurfactants compared to the control group larvae [ 100 ].…”

TmSpz-like Plays a Fundamental Role in Response to E. coli but Not S. aureus or C. albican Infection in Tenebrio molitor via Regulation of Antimicrobial Peptide Production

“…This suggests that Spz proteins have promiscuous roles in the innate immunity of insects against pathogens [ 4 ]. Furthermore, Tm Spz proteins can function as central immune modulators for biosurfactant-mediated AMP production in T. molitor [ 5 ].…”

Host–Pathogen Interaction 3.0

“…Other established model systems are protozoa such as Acanthamoeba castellanii , which was used to study Salmonella enterica sv. Typhimurium [ 2 ], the yellow mealworm Tenebrio molitor , which was analyzed in respect to antimicrobial peptide production in several of the submitted manuscripts [ 3 , 4 , 5 ], and larvae of the greater wax moth Galleria mellonella [ 6 ].…”