No abstract

The purpose of this study was to investigate the production of chitin and chitosan from both the exuvium and whole body of mealworm (Tenebrio molitor) larvae. Chitin from the exuvium and whole body of T. molitor larvae was chemically extracted with acid and alkali solutions to achieve demineralization (DM) and deproteinization (DP), respectively. The average DM (%) and DP (%) on a dry weight (DW) basis was 32.56 and 73.16% from larval exuvium, and 41.68 and 91.53% from whole body, respectively. To obtain chitosan, chitin particles from the exuvium and whole body of T. molitor larva were heated at various temperatures in different concentrations of NaOH. Average chitin yields were 18.01% and 4.92% of DW from the exuvium and whole body, respectively. The relative average yield of chitosan from whole body was 3.65% of DW. On average, over 90% of chitosan derived from whole body was deacetylated. The viscosity of chitosan from whole body was ranged from 48.0 cP to 54.0 cP. The chitin content of dry and wet byproducts from whole body were 17.32% and 16.94% respectively, compared to dry weight. The chitosan contents of byproducts on a DW basis were 14.48% in dry and 13.07% in wet byproduct. These results indicate that the exuvium and whole body of T. molitor larva may serve as a source of chitin and chitosan for use in domestic animal feed.

Chitin and chitosan were extracted from all specimens of Type I and II two-spotted field crickets (Gryllus bimaculatus) following chemical treatment with an acid and alkali. For chitin extraction, 2 N HCl and 1.25 N NaOH solutions were used to achieve demineralization and deproteinization, respectively. For chitosan extraction, 50 % NaOH (w/v) and 50 % NaOH (w/w) solutions were used to achieve deacetylation. Chitosan yielded from adult exoskeletons of G. bimaculatus in Test A of Type I was 1.76 and 8.40 % on a fresh weight (FW) and dry weight (DW) basis, respectively, after treatment with 50 % NaOH (w/v) at 95°C for 3 h. Furthermore, the chitosan yielded in Test D of Type II was 1.79 and 7.06 % on FW and DW basis, respectively, after treatment with 50 % NaOH (w/w) at 105°C for 3 h. The average yield of chitin and chitosan was 2.42 and 1.65 % on a FW basis, and 10.91 and 7.50 % on DW basis, respectively. The deacetylation (%) of chitosan extracted from adult exoskeletons in Tests A, B, C1, C2, D1, and D2 were 81.2 %, 14.5 %, 19.6 %, 90.7 %, 17.1 %, and 95.5 %, respectively. The viscosities of the chitosans extracted from adult exoskeletons in Tests A, C2, and D2 were 32.0, 21.6, and 62.4 cP (centi Poise), respectively. The molecular weight of chitosan from adult exoskeletons of G. bimaculatus was 308.3 kDa. Our results indicate that adult exoskeletons of G. bimaculatus could be used as a source of chitin and chitosan for use as functional additives in industrial animal feeds.

Dorsal, a member of the nuclear factor-kappa B (NF-κB) family of transcription factors, is a critical downstream component of the Toll pathway that regulates the expression of antimicrobial peptides (AMPs) against pathogen invasion. In this study, the full-length ORF of Dorsal was identified from the RNA-seq database of the mealworm beetle Tenebrio molitor (TmDorX2). The ORF of TmDorX2 was 1,482 bp in length, encoding a polypeptide of 493 amino acid residues. TmDorX2 contains a conserved Rel homology domain (RHD) and an immunoglobulin-like, plexins, and transcription factors (IPT) domain. TmDorX2 mRNA was detected in all developmental stages, with the highest levels observed in 3-day-old adults. TmDorX2 transcripts were highly expressed in the adult Malpighian tubules (MT) and the larval fat body and MT tissues. After challenging the larvae with Staphylococcus aureus and Escherichia coli, the TmDorX2 mRNA levels were upregulated 6 and 9 h post infection in the whole body, fat body, and hemocytes. Upon Candida albicans challenge, the TmDorX2 mRNA expression were found highest at 9 h post-infection in the fat body. In addition, TmDorX2-knockdown larvae exposed to E. coli, S. aureus, or C. albicans challenge showed a significantly increased mortality rate. Furthermore, the expression of 11 AMP genes was downregulated in the gut and fat body of dsTmDorX2-injected larvae upon E. coli challenge. After C. albicans and S. aureus challenge of dsTmDorX2-injected larvae, the expression of 11 and 10 AMPs was downregulated in the gut and fat body, respectively. Intriguingly, the expression of antifungal transcripts TmTenecin-3 and TmThaumatin-like protein-1 and -2 was greatly decreased in TmDorX2-silenced larvae in response to C. albicans challenge, suggesting that TmDorX2 regulates antifungal AMPs in the gut in response to C. albicans infection. The AMP expression profiles in the fat body, hemocytes, gut, and MTs suggest that TmDorX2 might have an important role in promoting the survival of T. molitor larvae against all mentioned pathogens.

Cactin was originally identified as an interactor of the Drosophila IκB factor Cactus and shown to play a role in controlling embryonic polarity and regulating the NF-κB signaling pathway. While subsequent studies have identified the roles for Cactin in the mammalian immune response, the immune function of Cactin in insects has not been described yet. Here, we identified a Cactin gene from the mealworm beetle, Tenebrio molitor (TmCactin) and characterized its functional role in innate immunity. TmCactin was highly expressed in prepupa to last instar stages, and its expression was high in the integument and Malpighian tubules of last instar larvae and adults. TmCactin was induced in larvae after infection with different pathogens and detectable within 3 hours of infection. The highest levels of TmCactin expression were detected at 9 hours post infection. TmCactin RNAi significantly decreased the survival rates of larvae after challenge with Escherichia coli and Staphylococcus aureus, but had no significant effect after challenge with Candida albicans. Furthermore, TmCactin RNAi significantly reduced the expression of seven antimicrobial peptide genes (AMPs) after bacterial challenge. Our results suggest that TmCactin may serve as an important regulator of innate immunity, mediating AMP responses against both Gram-positive and Gram-negative bacteria in T. molitor.