Insect antimicrobial peptides and their applications

ABC Transporter DerAB of Lactobacillus casei Mediates Resistance against Insect-Derived Defensins

Bce-like systems mediate resistance against antimicrobial peptides in Firmicutes bacteria. Lactobacillus casei BL23 encodes an "orphan" ABC transporter that, based on homology to BceAB-like systems, was proposed to contribute to antimicrobial peptide resistance. A mutant lacking the permease subunit was tested for sensitivity against a collection of peptides derived from bacteria, fungi, insects, and humans. Our results show that the transporter specifically conferred resistance against insect-derived cysteine-stabilized αβ defensins, and it was therefore renamed DerAB for defensin resistance ABC transporter. Surprisingly, cells lacking DerAB showed a marked increase in resistance against the lantibiotic nisin. This could be explained by significantly increased expression of the antimicrobial peptide resistance determinants regulated by the Bce-like systems PsdRSAB (formerly module 09) and ApsRSAB (formerly module 12). Bacterial two-hybrid studies in Escherichia coli showed that DerB could interact with proteins of the sensory complex in the Psd resistance system. We therefore propose that interaction of DerAB with this complex in the cell creates signaling interference and reduces the cell's potential to mount an effective nisin resistance response. In the absence of DerB, this negative interference is relieved, leading to the observed hyperactivation of the Psd module and thus increased resistance to nisin. Our results unravel the function of a previously uncharacterized Bce-like orphan resistance transporter with pleiotropic biological effects on the cell.IMPORTANCE Antimicrobial peptides (AMPs) play an important role in suppressing the growth of microorganisms. They can be produced by bacteria themselves-to inhibit competitors-but are also widely distributed in higher eukaryotes, including insects and mammals, where they form an important component of innate immunity. In low-GC-content Gram-positive bacteria, BceAB-like transporters play a crucial role in AMP resistance but have so far been primarily associated with interbacterial competition. Here, we show that the orphan transporter DerAB from the lactic acid bacterium Lactobacillus casei is crucial for high-level resistance against insect-derived AMPs. It therefore represents an important mechanism for interkingdom defense. Furthermore, our results support a signaling interference from DerAB on the PsdRSAB module that might prevent the activation of a full nisin response. The Bce modules from L. casei BL23 illustrate a biological paradox in which the intrinsic nisin detoxification potential only arises in the absence of a defensin-specific ABC transporter.

Partner-specific induction of Spodoptera frugiperda immune genes in response to the entomopathogenic nematobacterial complex Steinernema carpocapsae-Xenorhabdus nematophila

The Steinernema carpocapsae-Xenorhabdus nematophila association is a nematobacterial complex used in biological control of insect crop pests. The infection success of this dual pathogen strongly depends on its interactions with the host's immune system. Here, we used the lepidopteran pest Spodoptera frugiperda to analyze the respective impact of each partner in the induction of its immune responses. First, we used previously obtained RNAseq data to construct the immunome of S. frugiperda and analyze its induction. We then selected representative genes to study by RT-qPCR their induction kinetics and specificity after independent injections of each partner. We showed that both X. nematophila and S. carpocapsae participate in the induction of stable immune responses to the complex. While X. nematophila mainly induces genes classically involved in antibacterial responses, S. carpocapsae induces lectins and genes involved in melanization and encapsulation. We discuss putative relationships between these differential inductions and the pathogen immunosuppressive strategies.

De novo transcriptome of the whole-body of the gastropod mollusk Philomycus bilineatus, a pest with medical potential in China

Philomycus bilineatus is a highly common gastropod mollusk pest in China and is also utilized to treat infectious diseases. However, no genomic resources are available for this non-model species. In the present study, the transcriptomic analysis of P. bilineatus was completed. After sequencing using the next generation sequencing technology, 9.11 Gb of clean reads were obtained, which led to the assembly and annotation of 145,523 transcripts and 125,690 unigenes. Unigenes were functionally classified using Gene Ontology (GO), euKaryotic Ortholog Groups of proteins (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG). A total of 27,554 unigenes were assigned into 55 GO terms, 13,989 unigenes were differentiated into 26 KOG categories, and 16,368 unigenes were assigned to 229 KEGG pathways. Furthermore, 16,614 simple sequence repeats (SSRs), 38 olfactory genes, and 40 antimicrobial peptide/protein genes were identified. The transcriptome profile of P. bilineatus will provide a valuable genomic resource for further study, will promote the development of new pest management strategies through interference of chemosensory communication, and will support potential medicinal uses of this species.

The Effect of Hydrolyzed Insect Meals in Sea Trout Fingerling (Salmo trutta m. trutta) Diets on Growth Performance, Microbiota and Biochemical Blood Parameters

Simple Summary

The replacement of fishmeal by environmentally sustainable alternative meals has been one of the targets in aquaculture in recent decades. A number of factors support the use of insect meals, as a group of products characterized by high crude protein and crude fat content, in fish nutrition. Insects are readily accepted by a number of fish species, and they are part of the natural diet of omnivorous and carnivorous species. The present study was conducted to evaluate the effects of hydrolyzed Tenebrio molitor and Zophobas morio meals as a partial replacement for fishmeal in sea trout (Salmo trutta m. trutta) diets on growth performance, feed utilization, organosomatic indices, serum biochemistry, gut histology, and microbiota. In the present study, insect meals inclusion did not cause any adverse impacts on growth performance, feed utilization or gut histomorphology. However, an effect on the organosomatic indices, serum biochemistry, and microbiota was observed. In conclusion, hydrolyzed T. molitor and Z. morio meals seem to be promising alternative protein sources for sea trout nutrition.

Abstract

The present study is the first introduction of hydrolyzed superworm meal in sea trout nutrition. It was conducted to evaluate the effects of inclusion in the diet of hydrolyzed insect meals as a partial replacement for fishmeal on growth performance, feed utilization, organosomatic indices, serum biochemical parameters, gut histomorphology, and microbiota composition of sea trout (Salmo trutta m. trutta). The experiment was performed on 225 sea trout fingerlings distributed into three groups (3 tanks/treatment, 25 fish/tank). The control diet was fishmeal-based. In the experimental groups, 10% of hydrolyzed mealworm (TMD) and superworm (ZMD) meals were included. The protein efficiency ratio was lower in the TMD and ZMD. Higher organosomatic indices and liver lipid contents were found in the group fed ZMD. The ZMD increased levels of aspartate aminotransferase, and decreased levels of alkaline phosphatase. The Aeromonas spp. and Enterococcus spp. populations decreased in the ZMD. The concentrations of the Carnobacterium spp. decreased in the ZMD and TMD, as did that of the Lactobacillus group in the TMD. In conclusion, insect meals may be an alternative protein source in sea trout nutrition, as they yield satisfying growth performance and have the capability to modulate biochemical blood parameters and microbiota composition.

Therapeutic potential of a designed CSαβ peptide ID13 in Staphylococcus aureus-induced endometritis of mice

Staphylococcus aureus is a common pathogen that can cause clinical and subclinical endometritis in humans and animals. In this study, a designed CSαβ peptide ID13 from DLP4 exhibited high stable antibacterial activity in simulated gastric fluid (90.79%), serum (99.54%), and different pH buffers (> 99%) against S. aureus CVCC 546 and lower cytotoxicity (89.62% viability) than its parent peptide DLP4 (74.14% viability) toward mouse endometrial epithelial cells (MEECs). ID13 caused a depolarization of bacterial membrane and downregulation of the expression of genes involved in membrane potential maintenance and biofilm formation. The in vitro efficacy analysis of ID13 showed a synergistic effect with vancomycin, ampicillin, rifampin, and ciprofloxacin; intracellular antimicrobial activity against S. aureus CVCC 546 in MEECs; and the ability to inhibit lipoteichoic acid-induced pro-inflammatory cytokines from RAW 264.7. In the S. aureus-induced endometritis of mice, similar to vancomycin, ID13 remarkably alleviated pathological conditions, inhibited the production of cytokines (TNF-α, IL-1ß, IL-6, and IL-10), and suppressed the TLR2-NF-κB signal pathway. Collectively, these results suggest that ID13 could be a potential candidate peptide for therapeutic application in S. aureus-induced endometritis. Key Points •Higher antibacterial activity and lower hemolysis of ID13 than DLP4. •ID13 could downregulate the genes of bacterial survival and infection. •ID13 could alleviate the S. aureus-induced endometritis of mice. •ID13 could regulate the cytokines and suppress the TLR2-NF-κB signal pathway.

An Enhanced Variant Designed From DLP4 Cationic Peptide Against Staphylococcus aureus CVCC 546

Insect defensins are promising candidates for the development of potent antimicrobials against antibiotic-resistant Staphylococcus aureus (S. aureus). An insect defensin, DLP4, isolated from the hemolymph of Hermetia illucens larvae, showed low antimicrobial activity against Gram-positive (G+) pathogens and high cytotoxicity, which limited its effective therapeutic application. To obtain more potent and low cytotoxicity molecules, a series of peptides was designed based on the DLP4 template by changing the conservative site, secondary structure, charge, or hydrophobicity. Among them, a variant designated as ID13 exhibited strong antibacterial activity at low MIC values of 4-8 μg/mL to G+ pathogens (S. aureus: 4 μg/mL; Staphylococcus epidermidis: 8 μg/mL; Streptococcus pneumoniae: 4 μg/mL; Streptococcus suis: 4 μg/mL), which were lower than those of DLP4 (S. aureus: 16 μg/mL; S. epidermidis: 64 μg/mL; S. pneumoniae: 32 μg/mL; S. suis: 16 μg/mL), and cytotoxicity of ID13 (71.4% viability) was less than that of DLP4 (63.8% viability). ID13 could penetrate and destroy the cell membrane of S. aureus CVCC 546, resulting in an increase in potassium ion leakage; it bound to genomic DNA (gDNA) and led to the change of gDNA conformation. After treatment with ID13, perforated, wrinkled, and collapsed S. aureus CVCC 546 cells were observed in electron microscopy. Additionally, ID13 killed over 99.99% of S. aureus within 1 h, 2 × MIC of ID13 induced a post-antibiotic effect (PAE) of 12.78 ± 0.28 h, and 10 mg/kg ID13 caused a 1.8 log10 (CFU/g) (CFU: colony-forming units) reduction of S. aureus in infected mouse thigh muscles and a downregulation of TNF-α, IL-6, and IL-10 levels, which were superior to those of DLP4 or vancomycin. These findings indicate that ID13 may be a promising peptide antimicrobial agent for therapeutic application.

Insight Into the Effects of Nisin and Cecropin on the Oral Microbial Community of Rats by High-Throughput Sequencing

The oral microbiome has major impacts on oral health and disease. Antimicrobial peptides (AMPs), such as nisin and cecropin, have been widely used as food preservatives or feed additives, and are thus inevitably ingested by consumers through their oral cavity. However, as broad-spectrum antimicrobial reagents, the effect of AMPs on the oral microbiome of consumer's remains poorly characterized. In this study, we performed 16S rDNA high-throughput sequencing to investigate the effect of nisin and cecropin on the oral microbiomes of rats. Our results suggest that although nisin and cecropin have different effects on the oral microbiome of rats, both AMPs impact the composition of oral microbial communities at the phylum and genus levels. Cecropin significantly reduced the diversity and richness of rat oral microbial communities. Notably, the relative abundance of the pathogen Acinetobacter baumannii increased in the oral microbial community of rats fed cecropin-containing feed. In addition, nisin significantly reduced the amount of secretory immunoglobulin A in the saliva of rats.

A Hybrid Peptide DEFB-TP5 Expressed in Methylotrophic Yeast Neutralizes LPS With Potent Anti-inflammatory Activities

DEFB-TP5 is a novel auspicious health-beneficial peptide derivative from two naturally occurring peptides, β-Defensin (DEFB) and thymopentin (TP5), and shows strong anti-inflammatory activity and binds to LPS without cytotoxicity and hemolytic effect. Furthermore, the application of DEFB-TP5 peptide is inadequate by its high cost. In the current study, we developed a biocompatible mechanism for expression of the DEFB-TP5 peptide in Pichia pastoris. The transgenic strain of hybrid DEFB-TP5 peptide with a molecular weight of 6.7kDa as predictable was obtained. The recombinant DEFB-TP5 peptide was purified by Ni-NTA chromatography, estimated 30.41 mg/L was obtained from the cell culture medium with 98.2% purity. Additionally, The purified DEFB-TP5 peptide significantly (p< 0.05) diminished the release of nitric oxide (NO), TNF-α, IL-6, IL-1β in LPS-stimulated RAW264.7 macrophages in a dose-dependent manner. This study will not only help to understand the molecular mechanism of expression that can potentially be used to develop an anti-endotoxin peptide but also to serve as the basis for the development of antimicrobial and anti-inflammatory agents as well, which also provides a potential source for the production of recombinant bioactive DEFB-TP5 at the industrial level.

iTRAQ-Based Comparative Proteomic Analysis of Larval Midgut From the Beet Armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) Challenged With the Entomopathogenic Bacteria Serratia marcescens

Entomopathogenic bacteria Serratia marcescens is widely used as an environmentally friendly biocontrol agent against various pests, including Spodoptera exigua. Understanding the immune defense mechanism of S. exigua through comparative proteomic analysis can identify the key proteins expressed in response to the microbial infection. Here, we employed the as isobaric tags for relative and absolute quantification (iTRAQ) technique to investigate the effects of S. marcescens on the proteomic expression of S. exigua. Based on the molecular functional analysis, the differentially expressed proteins (DEPs) were mainly involved in the binding process and catalytic activities. Further bioinformatics analysis revealed important DEPs that played a crucial role in innate immunity of S. exigua with recognition (C-type lectin), melanization (propanol oxidase 3, serine protease, Serine-type carboxypeptidase activity, clip domain serine protease 4), antimicrobial activity (lysozyme, lysozyme-like, gloverin, cecropin B), detoxification (acetyl-CoA C-acetyltransferase, 3-dehydroecdysone 3-alpha-reductase, glucuronosyltransferase, glutathione S-transferase) and others. The Quantitative real-time PCR (qRT-PCR) results further indicated the significant upregulation of the immune-related genes in Spodoptera exigua following S. marcescens infection. To the best of our knowledge, this is the first iTRAQ based study to characterize S. marcescens mediated proteomic changes in S. exigua and identified important immune-related DEPs. The results of this study will provide an essential resource for understanding the host-pathogen interactions and the development of novel microbial biopesticides against various pests.

Immunological Function of the Antibacterial Peptide Attacin-Like in the Chinese Oak Silkworm, Antheraea pernyi

BACKGROUND

Antibacterial peptides play important roles in the innate immune system of insects and are divided into four categories according to their structures. Although many antibacterial peptides have been reported in lepidopteran insects, the roles of an attacin-like gene in immune response of Antheraea pernyi remain unclear.

OBJECTIVE

In this study, the cloning and immunological functions of an attacin-like gene from Antheraea pernyi were investigated.

METHODS

The open reading frame of Ap-attacin-like gene was cloned by PCR using the specific primers and then was ligated to the pET-32a vector to construct the recombinant plasmids Ap-attacin- like-pET-32a. The recombinant Ap-attacin-like protein was expressed in E. coli (BL21 DE3) cells and purified by Ni-NTA affinity chromatography. The expression patterns of Ap-attacin-like in different tissues or under microorganism challenges were investigated by real-time PCR and western blotting. Finally, agar well diffusion assay was performed to determine the antimicrobial activity of the recombinant Ap-attacin-like proteins based on the inhibition rate.

RESULTS

The expression level of Ap-attacin-like was highest in the fat body compared with the other examined tissues. The expression of Ap-attacin-like in the fat body was significantly elevated after E. coli, Beauveria bassiana, Micrococcus luteus or Nuclear Polyhedrosis Virus challenges. In addition, the recombinant Ap-attacin-like proteins had obvious antibacterial activity against E. coli.

CONCLUSION

Ap-attacin-like was highly expressed in immune-related tissues and its expression level was significantly induced by different microorganism challenges, suggesting that Ap-attacin-like participated in the innate immunity of A. pernyi.

Dual oxidase Duox and Toll-like receptor 3 TLR3 in the Toll pathway suppress zoonotic pathogens through regulating the intestinal bacterial community homeostasis in Hermetia illucens L

Black soldier fly (BSF; Hermetia illucens L.) larvae can convert fresh pig manure into protein and fat-rich biomass, which can then be used as aquafeed for select species. Currently, BSF is the only approved insect for such purposes in Canada, USA, and the European Union. Pig manure could serve as a feed substrate for BSF; however, it is contaminated with zoonotic pathogens (e.g., Staphylococcus aureus and Salmonella spp.). Fortunately, BSF larvae inhibit many of these zoonotic pathogens; however, the mechanisms employed are unclear. We employed RNAi, qRT-PCR, and Illumina MiSeq 16S rDNA high-throughput sequencing to examine the interaction between two immune genes (Duox in Duox-reactive oxygen species [ROS] immune system and TLR3 in the Toll signaling pathway) and select pathogens common in pig manure to decipher the mechanisms resulting in pathogen suppression. Results indicate Bsf Duox-TLR3 RNAi increased bacterial load but decreased relative abundance of Providencia and Dysgonomonas, which are thought to be commensals in the BSF larval gut. Bsf Duox-TLR3 RNAi also inactivated the NF-κB signaling pathway, downregulated the expression of antimicrobial peptides, and diminished inhibitory effects on zoonotic pathogen. The resulting dysbiosis stimulated an immune response by activating BsfDuox and promoting ROS, which regulated the composition and structure of the gut bacterial community. Thus, BsfDuox and BsfTLR3 are important factors in regulating these key gut microbes, while inhibiting target zoonotic pathogens.

Proline-Rich Antimicrobial Peptides in Medicinal Maggots of Lucilia sericata Interact With Bacterial DnaK But Do Not Inhibit Protein Synthesis

In the search for new antibiotics to combat multidrug-resistant microbes, insects offer a rich source of novel anti-infectives, including a remarkably diverse array of antimicrobial peptides (AMPs) with broad activity against a wide range of species. Larvae of the common green bottle fly Lucilia sericata are used for maggot debridement therapy, and their effectiveness in part reflects the large panel of AMPs they secrete into the wound. To investigate the activity of these peptides in more detail, we selected two structurally different proline rich peptides (Lser-PRP2 and Lser-PRP3) in addition to the α-helical peptide Lser-stomoxyn. We investigated the mechanism of anti-Escherichia coli action of the PRPs in vitro and found that neither of them interfered with protein synthesis but both were able to bind the bacterial chaperone DnaK and are therefore likely to inhibit protein folding. However, unlike Lser-stomoxyn that permeabilized the bacterial membrane by 1% at the low concentration (0.25 µM) neither of the PRPs alone was able to permeabilize E. coli membrane. In the presence of this Lser-stomoxyn concentration significant increase in anti-E. coli activity of Lser-PRP2 was observed, indicating that this peptide needs specific membrane permeabilizing agents to exert its antibacterial activity. We then examined the AMPs-treated bacterial surface and observed detrimental structural changes in the bacterial cell envelope in response to combined AMPs. The functional analysis of insect AMPs will help select optimal combinations for targeted antimicrobial therapy.

Mitochondrial and Innate Immunity Transcriptomes from Spodoptera frugiperda Larvae Infected with the Spodoptera frugiperda Ascovirus

Ascoviruses are large, enveloped DNA viruses that induce remarkable changes in cellular architecture during which the cell is partitioned into numerous vesicles for viral replication. Previous studies have shown that these vesicles arise from a process resembling apoptosis yet which differs after nuclear lysis in that mitochondria are not degraded but are modified by the virus, changing in size, shape, and motility. Moreover, infection does not provoke an obvious innate immune response. Thus, we used in vivo RNA sequencing to determine whether infection by the Spodoptera frugiperda ascovirus 1a (SfAV-1a) modified expression of host mitochondrial, cytoskeletal, and innate immunity genes. We show that transcripts from many mitochondrial genes were similar to those from uninfected controls, whereas others increased slightly during vesicle formation, including those for ATP6, ATP8 synthase, and NADH dehydrogenase subunits, supporting electron microscopy (EM) data that these organelles were conserved for virus replication. Transcripts from 58 of 106 cytoskeletal genes studied increased or decreased more than 2-fold postinfection. More than half coded for mitochondrial motor proteins. Similar increases occurred for innate immunity transcripts and their negative regulators, including those for Toll, melanization, and phagocytosis pathways. However, those for many antimicrobial peptides, such as moricin, increased more than 20-fold. In addition, transcripts for gloverin-3, spod_x_tox, Hdd23, and lebocin, also antimicrobial, increased more than 20-fold. Interestingly, a phenoloxidase inhibitor transcript increased 12-fold, apparently to interfere with melanization. SfAV-1a destroys most fat body cells by 7 days postinfection, so innate immunity gene transcripts apparently occur in remaining cells in this tissue and possibly other major tissues, namely, epidermis and tracheal matrix.IMPORTANCE Ascoviruses are large DNA viruses that infect insects, inducing a cellular pathology that resembles apoptosis but which differs by causing enormous cellular hypertrophy followed by cleavage of the cell into numerous viral vesicles for replication. Previous EM studies suggest that mitochondria are important for vesicle formation. Transcriptome analyses of Spodoptera frugiperda larvae infected with SfAV-1a showed that mitochondrial transcripts were similar to those from uninfected controls or increased slightly during vesicle formation, especially for ATP6, ATP8 synthase, and NADH dehydrogenase subunits. This pattern resembles that for chronic disease-inducing viruses, which conserve mitochondria, differing markedly from viruses causing short-term viral diseases, which degrade mitochondrial DNA. Though mitochondrial transcript increases were low, our results demonstrate that SfAV-1a alters host mitochondrial expression more than any other virus. Regarding innate immunity, although SfAV-1a destroys most fat body cells, certain immunity genes were highly upregulated (greater than 20-fold), suggesting that these transcripts may originate from other tissues.

Analogs of Periplanetasin-4 Exhibit Deteriorated Membrane-Targeted Action

Periplanetasin-4 is an antimicrobial peptide with 13 amino acids identified in cockroaches. It has been reported to induce fungal cell death by apoptosis and membrane-targeted action. Analogs were designed by substituting arginine residues to modify the electrostatic and hydrophobic interactions accordingly and explore the effect of periplanetasin-4 through the increase of net charge and the decrease of hydrophobicity. The analogs showed lower activity than periplanetasin-4 against gram-positive and gram-negative bacteria. Similar to periplanetasin-4, the analogs exhibited slight hemolytic activity against human erythrocytes. Membrane studies, including determination of changes in membrane potential and permeability, and fluidity assays, revealed that the analogs disrupt less membrane integrity compared to periplanetasin-4. Likewise, when the analogs were treated to the artificial membrane model, the passage of molecules bigger than FD4 was difficult. In conclusion, arginine substitution could not maintain the membrane disruption ability of periplanetasin-4. The results indicated that the attenuation of hydrophobic interactions with the plasma membrane caused a reduction in the accumulation of the analogs on the membrane before the formation of electrostatic interactions. Our findings will assist in the further development of antimicrobial peptides for clinical use.

Midgut de novo transcriptome analysis and gene expression profiling of Spodoptera exigua larvae exposed with sublethal concentrations of Cry1Ca protein

Spodoptera exigua (Hübner) is a polyphagous pest on agricultural crops, whose control is based mainly on the application of chemical insecticides. Bacillus thuringiensis (Bt) is one of the most important biological agents that have been successfully applied as a biological control, and Cry1Ca protein is considered to be active against S. exigua. Therefore, to understand the response of S. exigua to Cry1Ca protein, high-throughput sequencing was used to analyse the S. exigua larval midgut after treatment with sublethal concentrations of Cry1Ca protein. Transcriptome data showed that a total of 98,571 unigenes with an N50 value of 1135 bp and a mean length of 653 bp were obtained. Furthermore, 2962 differentially expressed genes (DEGs) were identified after Cry1Ca challenge, including 1508 up-regulated and 1454 down-regulated unigenes. Among these DEGs, detoxification (CYP, CarE, and GST) and Bt resistance (ALP, APN, and ABC transporter)-related genes were differentially expressed in the midgut of S. exigua after Cry1Ca treatment. However, most DEGs of protective enzymes were down-regulated, while most DEGs related with serine protease and REPAT were up-regulated. Furthermore, almost all DEGs related to the immune signaling pathway, antimicrobial protein, and lysozyme were up-regulated by Cry1Ca treatment. These results indicated that the detoxification enzyme, protective enzymes, Bt resistance-related genes, serine protease, REPAT, and the immune response might have been involved in the response of S. exigua to Cry1Ca protein. In summary, analysis of the transcriptomal expression of genes involved in Cry1Ca protein against S. exigua provided potential clues for elucidating the host response processes and defensive mechanisms underlying Cry1Ca toxicity.

TmSpz6 Is Essential for Regulating the Immune Response to Escherichia Coli and Staphylococcus Aureus Infection in Tenebrio Molitor

Spätzle is an extracellular protein that activates the Toll receptor during embryogenesis and immune responses in Drosophila. However, the functions of the spätzle proteins in the innate immune response against bacteria or fungi in T. molitor are not well understood. Therefore, in this study, the open reading frame (ORF) of TmSpz6 was identified and its function in the response to bacterial and fungal infections in T. molitor was investigated using RNAi. The highest expression of TmSpz6 was in prepupae, and 3- and 6-day-old pupae, while remarkable expression was also observed in other stages. The tissue-specific expression analysis showed that TmSpz6 expression was highest in the hemocytes of larvae. TmSpz6 expression was highly induced when challenged with Escherichia coli, Staphylococcus aureus, or Candida albicans at 6 h post-injection; however, TmSpz6-silenced larvae were significantly more susceptible to only E. coli and S. aureus infection. The antimicrobial peptides (AMPs) gene expression analysis results show that TmSpz6 mainly positively regulated the expression of TmTencin-2 and -3 in response to E. coli and S. aureus infection. Collectively, these results suggest that TmSpz6 plays an important role in regulating AMP expression and increases the survival of T. molitor against E. coli and S. aureus.

Intestinal responses of the oriental fruit fly Bactrocera dorsalis (Hendel) after ingestion of an entomopathogenic bacterium strain

BACKGROUND

Bactrocera dorsalis (Hendel) is the main fruit fly pest of tropical and subtropical countries. The application of insecticides to manage this pest has led to serious resistance problems; therefore, new ways to control B. dorsalis are required. Pathogenic bacteria are sources of biocontrol agents for pest management.

RESULTS

We determined that a pathogenic bacterial strain, Serratia marcescens PS-1, isolated from a moribund striped flea beetle (Phyllotreta striolata), was lethal to B. dorsalis adults following ingestion. Histological analyses revealed that PS-1 damaged the intestinal epithelium, resulting in cell death within 24 h. We then generated a gut transcriptomic data set using RNA-Seq at two time points (6 and 24 h) after PS-1 infection. We found that genes encoding the peritrophic matrix constituent were down-regulated, whereas genes involved in lipid and glycan metabolism, and renewal of the gut epithelium, along with genes encoding digestive enzymes and stress response factors, were up-regulated. In addition, 14 cecropin genes were identified and cloned from B. dorsalis. To our knowledge, the number of cecropins identified in the present study is greater than that reported in the insects of earlier studies. Moreover, some of the cecropins identified were significantly down-regulated after PS-1 treatment.

CONCLUSION

Our findings provide new insights into the insect gut response to pathogenic bacterial invasion and may aid the development of new strategies for the biological control of B. dorsalis. © 2019 Society of Chemical Industry.

The unique antimicrobial peptide repertoire of stick insects

The comparative analysis of innate immunity across different insect taxa has revealed unanticipated evolutionary plasticity, providing intriguing examples of immunity-related effector gene expansion and loss. Phasmatodea, the stick and leaf insects, is an order of hemimetabolous insects that can provide insight into ancestral innate immunity genes lost by later insect clades. We injected the stick insect Peruphasma schultei with a mixture of microbial elicitors to activate a strong immune response, followed by RNA-Seq analysis to screen for induced immunity-related effector genes. This revealed a highly diverse spectrum of antimicrobial peptides (AMPs) belonging to the attacin, coleoptericin, defensin, thaumatin, and tachystatin families. In addition, we identified a large group of short, cysteine-rich putative AMPs, some of which were strongly elicited. The immunity-related effector gene repertoire also included c-type and i-type lysozymes and several pattern-recognition proteins, such as proteins that recognize Gram-negative bacteria and peptidoglycans. Finally, we identified 45 hemolymph lipopolysaccharide-binding protein sequences, an unusually large number for insects. Taken together, our results indicate that at least some phasmids synthesize a broad spectrum of diverse AMPs that deserve further in-depth analysis.

Antimicrobial peptides fromBombyx mori: a splendid immune defense response in silkworms

Bombyx mori L., a primary producer of silk, is the main tool in the sericulture industry and provides the means of livelihood to a large number of people. Silk cocoon crop losses due to bacterial infection pose a major threat to the sericulture industry. Bombyx mori L., a silkworm of the mulberry type, has a sophisticated inherent innate immune mechanism to combat such invasive pathogens. Among all the components in this defense system, antimicrobial peptides (AMPs) are notable due to their specificity towards the invading pathogens without harming the normal host cells. Bombyx mori L. so far has had AMPs identified that belong to six different families, namely cecropin, defensin, moricin, gloverin, attacin and lebocin, which are produced by the Toll and immune deficiency (IMD) pathways. Their diverse modes of action depend on microbial pathogens and are still under investigation. This review examines the recent progress in understanding the immune defense mechanism of Bombyx mori based on AMPs.

AMPs produced by B. mori induced by microbial challenge in the fat body.

Characterization of the active fragments of Spodoptera litura Lebocin-1

Insects can produce various antimicrobial peptides (AMPs) upon immune stimulation. One class of AMPs are characterized by their high proline content in certain fragments. They are generally called proline-rich antimicrobial peptides (PrAMPs). We previously reported the characterization of Spodoptera litura lebocin-1 (SlLeb-1), a PrAMP proprotein. Preliminary studies with synthetic polypeptides showed that among the four deductive active fragments, the C-terminal fragment SlLeb-1 (124-158) showed strong antibacterial activities. Here, we further characterized the antibacterial and antifungal activities of 124-158 and its four subfragments: 124-155, 124-149, 127-158, and 135-158. Only 124-158 and 127-158 could agglutinate bacteria, while 124-158 and four subfragments all could agglutinate Beauveria bassiana spores. Confocal microscopy showed that fluorescent peptides were located on the microbial surface. Fragment 135-158 lost activity completely against Escherichia coli and Staphylococcus aureus, and partially against Bacillus subtilis. Only 124-149 showed low activity against Serratia marcescens. Negative staining, transmission, and scanning electron microscopy of 124-158 treated bacteria showed different morphologies. Flow cytometry analysis of S. aureus showed that 124-158 and four subfragments changed bacterial subpopulations and caused an increase of DNA content. These results indicate that active fragments of SlLeb-1 may have diverse antimicrobial effects against different microbes. This study may provide an insight into the development of novel antimicrobial agents.

Insect Defense Proteins and Peptides

The composition of insect hemolymph can change depending on many factors, e.g. access to nutrients, stress conditions, and current needs of the insect. In this chapter, insect immune-related polypeptides, which can be permanently or occasionally present in the hemolymph, are described. Their division into peptides or low-molecular weight proteins is not always determined by the length or secondary structure of a given molecule but also depends on the mode of action in insect immunity and, therefore, it is rather arbitrary. Antimicrobial peptides (AMPs) with their role in immunity, modes of action, and classification are presented in the chapter, followed by a short description of some examples: cecropins, moricins, defensins, proline- and glycine-rich peptides. Further, we will describe selected immune-related proteins that may participate in immune recognition, may possess direct antimicrobial properties, or can be involved in the modulation of insect immunity by both abiotic and biotic factors. We briefly cover Fibrinogen-Related Proteins (FREPs), Down Syndrome Cell Adhesion Molecules (Dscam), Hemolin, Lipophorins, Lysozyme, Insect Metalloproteinase Inhibitor (IMPI), and Heat Shock Proteins. The reader will obtain a partial picture presenting molecules participating in one of the most efficient immune strategies found in the animal world, which allow insects to inhabit all ecological land niches in the world.

Enzymatic hydrolysis of insectAlphitobius diaperinustowards the development of bioactive peptide hydrolysates

Edible insects are a promising protein source for the future generation, due to their nutritional composition, sustainability and low environmental impact.

Pattern recognition receptors in Drosophila immune responses

Insects, which lack the adaptive immune system, have developed sophisticated innate immune system consisting of humoral and cellular immune responses to defend against invading microorganisms. Non-self recognition of microbes is the front line of the innate immune system. Repertoires of pattern recognition receptors (PRRs) recognize the conserved pathogen-associated molecular patterns (PAMPs) present in microbes, such as lipopolysaccharide (LPS), peptidoglycan (PGN), lipoteichoic acid (LTA) and β-1, 3-glucans, and induce innate immune responses. In this review, we summarize current knowledge of the structure, classification and roles of PRRs in innate immunity of the model organism Drosophila melanogaster, focusing mainly on the peptidoglycan recognition proteins (PGRPs), Gram-negative bacteria-binding proteins (GNBPs), scavenger receptors (SRs), thioester-containing proteins (TEPs), and lectins.

Insect Cecropins, Antimicrobial Peptides with Potential Therapeutic Applications

The alarming escalation of infectious diseases resistant to conventional antibiotics requires urgent global actions, including the development of new therapeutics. Antimicrobial peptides (AMPs) represent potential alternatives in the treatment of multi-drug resistant (MDR) infections. Here, we focus on Cecropins (Cecs), a group of naturally occurring AMPs in insects, and on synthetic Cec-analogs. We describe their action mechanisms and antimicrobial activity against MDR bacteria and other pathogens. We report several data suggesting that Cec and Cec-analog peptides are promising antibacterial therapeutic candidates, including their low toxicity against mammalian cells, and anti-inflammatory activity. We highlight limitations linked to the use of peptides as therapeutics and discuss methods overcoming these constraints, particularly regarding the introduction of nanotechnologies. New formulations based on natural Cecs would allow the development of drugs active against Gram-negative bacteria, and those based on Cec-analogs would give rise to therapeutics effective against both Gram-positive and Gram-negative pathogens. Cecs and Cec-analogs might be also employed to coat biomaterials for medical devices as an approach to prevent biomaterial-associated infections. The cost of large-scale production is discussed in comparison with the economic and social burden resulting from the progressive diffusion of MDR infectious diseases.

Antimicrobial peptides: new hope in the war against multidrug resistance

The discovery of antibiotics marked a golden age in the revolution of human medicine. However, decades later, bacterial infections remain a global healthcare threat, and a return to the pre-antibiotic era seems inevitable if stringent measures are not adopted to curb the rapid emergence and spread of multidrug resistance and the indiscriminate use of antibiotics. In hospital settings, multidrug resistant (MDR) pathogens, including carbapenem-resistant Pseudomonas aeruginosa, vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamases (ESBL) bearing Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae are amongst the most problematic due to the paucity of treatment options, increased hospital stay, and exorbitant medical costs. Antimicrobial peptides (AMPs) provide an excellent potential strategy for combating these threats. Compared to empirical antibiotics, they show low tendency to select for resistance, rapid killing action, broad-spectrum activity, and extraordinary clinical efficacy against several MDR strains. Therefore, this review highlights multidrug resistance among nosocomial bacterial pathogens and its implications and reiterates the importance of AMPs as next-generation antibiotics for combating MDR superbugs.

Exploring the Role of Relish on Antimicrobial Peptide Expressions (AMPs) Upon Nematode-Bacteria Complex Challenge in the Nipa Palm Hispid Beetle, Octodonta nipae Maulik (Coleoptera: Chrysomelidae)

The humoral immune responses of the nipa palm hispid beetle Octodonta nipae involves the inducible expression of the genes coding for antimicrobial peptides (AMPs) which are mediated by immune deficiency signaling pathways. In insects, the nuclear factor-κB (NF-κB) transcription factor, Relish, has been shown to regulate AMP gene expressions upon microbial infections. Here, we dissect the expression patterns of some AMPs in O. nipae during infections by entomopathogenic nematodes (EPNs) and their symbionts, before and after Relish knock down. Our results indicate that, prior to gene silencing, the AMPs attacin C1, attacin C2, and defensin 2B were especially expressed to great extents in the insects challenged with the nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora as well as with their respective symbionts Xenorhabdus nematophila and Photorhabdus luminescens. The study also established the partial sequence of OnRelish/NF-κB p110 subunit in O. nipae, with an open reading frame coding for a protein with 102 amino acid residues. A typical Death domain-containing protein was detected (as seen in Drosophila) at the C-terminus of the protein. Phylogenetic analysis revealed that in O. nipae, Relish is clustered with registered Relish/NF-κB p110 proteins from other species of insect especially Leptinotarsa decemlineata from the same order Coleoptera. Injection of OnRelish dsRNA remarkably brought down the expression of OnRelish and also reduced the magnitude of transcription of attacin C1 and defensin 2B upon S. carpocapsae and H. bacteriophora and their symbionts infections. Altogether, our data unveil the expression pattern of OnRelish as well as that of some AMP genes it influences during immune responses of O. nipae against EPNs and their symbionts.

Functional Characterization of Outer Membrane Proteins (OMPs) in Xenorhabdus nematophila and Photorhabdus luminescens through Insect Immune Defense Reactions

Xenorhabdus nematophila and Photorhabdusluminescens are entomopathogenic bacterial symbionts that produce toxic proteins that can interfere with the immune system of insects. Herein, we show that outer membrane proteins (OMPs) could be involved as bacterial virulence factors. Purified totals OMPs of both bacterial species were injected into fifth instar larvae of Spodopteraexigua Hübner. Larvae were surveyed for cellular defenses fluctuations in total haemocyte counts (THC) and granulocyte percentage and for the humoral defenses protease, phospholipase A2 (PLA₂), and phenoloxidase (PO) activities at specific time intervals. Changes in the expression of the three inducible antimicrobial peptides (AMPs), cecropin, attacin, and spodoptericin, were also measured. Larvae treated with OMPs of both bacterial species had more haemocytes than did the negative controls. OMPs of X. nematophila caused more haemocyte destruction than did the OMPs of P. luminescens. The OMPs of both bacterial species initially activated insect defensive enzymes post-injection, the degree of activation varying with enzyme type. The AMPs, attacin, cecropin, and spodoptericin were up-regulated by OMP injections compared with the normal larvae. The expression of these three AMPs was maximal at four hours post injection (hpi) with P. luminescens OMPs treatment. Expression of the three AMPs in X. nematophila treated insects was irregular and lower than in the P. luminescens OMPs treatment. These findings provide insights into the role of OMPs of entomopathogenic nematode bacterial symbionts in countering the physiological defenses of insects.

Molecular Identification of a Moricin Family Antimicrobial Peptide (Px-Mor) From Plutella xylostella With Activities Against the Opportunistic Human Pathogen Aureobasidium pullulans

Antimicrobial peptides (AMPs) represent the largest group of endogenous compounds and serves as a novel alternative to traditional antibiotics for the treatment of pathogenic microorganisms. Moricin is an important α-helical AMP plays a crucial role in insect humoral defense reactions. The present study was designed to identify and characterize novel AMP moricin (Px-Mor) from diamondback moth (Plutella xylostella) and tested its activity against bacterial and fungal infection including the opportunistic human pathogen Aureobasidium pullulans. Molecular cloning of Px-Mor using rapid amplification of cDNA ends revealed a 482 bp full length cDNA with 198 bp coding region. The deduced protein sequence contained 65 amino acids, and the mature peptides contained 42 amino acid residues with a molecular mass of 4.393 kDa. Expression analysis revealed that Px-Mor was expressed throughout the life cycle of P. xylostella with the highest level detectable in the fourth instar and prepupa stage. Tissue specific distribution showed that Px-Mor was highly expressed in fat body and hemocyte. In vitro, antimicrobial assays indicated that Px-Mor exhibited a broad antimicrobial spectrum against Gram positive bacteria (GPB), Gram negative bacteria (GNB) and fungi. Moreover, scanning electron microscopy and transmission electron microscopy (TEM) revealed that Px-Mor can cause obvious morphological alterations in A. pullulans, which demonstrated its powerful effect on the mycelia growth inhibition. Taken together, these results indicate that Px-Mor plays an important role in the immune responses of P. xylostella and can be further exploited as an antimicrobial agent against various diseases including for the treatment of A. pullulans infection.

Identification of novel antimicrobial peptides from rice planthopper, Nilaparvata lugens

In this study, two novel antibacterial peptide genes, termed lugensin A and B were identified and characterized from a rice sap-sucking hemipteran insect pest, the brown planthopper, Nilaparvata lugens. Lugensin gene expression was significantly induced by Gram-negative and Gram-positive bacterial stains under the regulation of a signal receptor, the long peptidoglycan recognition protein (PGRP-LC) in the IMD pathway. Knockdown of PGRP-LC by RNAi eliminated bacterium induced Lugensin gene expression. Lugensins had the apparent antibacterial activities against Escherichia coli K12, Bacillus subtilis and the rice bacterial brown stripe pathogen Acidovorax avenae subsp. avenae (Aaa) strain RS-1. Lugensins inhibited bacterial proliferation by disrupting the integrity of the bacterial membranes. Scanning electron microscopy revealed abnormal membrane morphology of the recombinant Lugensin-treated bacteria. Lugensins induced complete cell disruption of E. coli K12 and B. subtilis strains while formed the holes on the cell surface of Aaa RS-1 strain. Immunofluorescence showed that Lugensins localized in the cell membrane of E. coli K12 while accumulated in the cytosol of B. subtilis. Differently, Lugensins remained in both the cell membrane and the cytosol of Aaa RS-1 strain, suggesting different action modes of Lugensins to different microbes. This is the first report of the novel antibacterial peptides found in the rice sap-sucking hemipteran insect species.

Trans-generational Immune Priming in Invertebrates: Current Knowledge and Future Prospects

Trans-generational immune priming (TGIP) refers to the transfer of the parental immunological experience to its progeny. This may result in offspring protection from repeated encounters with pathogens that persist across generations. Although extensively studied in vertebrates for over a century, this phenomenon has only been identified 20 years ago in invertebrates. Since then, invertebrate TGIP has been the focus of an increasing interest, with half of studies published during the last few years. TGIP has now been tested in several invertebrate systems using various experimental approaches and measures to study it at both functional and evolutionary levels. However, drawing an overall picture of TGIP from available studies still appears to be a difficult task. Here, we provide a comprehensive review of TGIP in invertebrates with the objective of confronting all the data generated to date to highlight the main features and mechanisms identified in the context of its ecology and evolution. To this purpose, we describe all the articles reporting experimental investigation of TGIP in invertebrates and propose a critical analysis of the experimental procedures performed to study this phenomenon. We then investigate the outcome of TGIP in the offspring and its ecological and evolutionary relevance before reviewing the potential molecular mechanisms identified to date. In the light of this review, we build hypothetical scenarios of the mechanisms through which TGIP might be achieved and propose guidelines for future investigations.

Cecropin-like antimicrobial peptide protects mice from lethal E.coli infection

Resistance of pathogenic bacteria to standard antibiotics is an issue of great concern, and new treatments for bacterial infections are needed. Antimicrobial peptides (AMPs) are small, cationic, and amphipathic molecules expressed by metazoans that kill pathogens. They are a key part of the innate immune system in both vertebrates and invertebrates. Due to their low toxicity and broad antimicrobial activities, there has been increasing attention to their therapeutic usage. Our previous research demonstrated that four peptides-DAN1, DAN2, HOLO1 and LOUDEF1-derived from recently sequenced arthropod genomes exhibited potent antimicrobial effects in-vitro. In this study, we show that DAN2 protected 100% of mice when it was administered at a concentration of 20 mg/kg thirty minutes after the inoculation of a lethal dose of E. coli intraperitoneally. Lower concentrations of DAN2-10mg/kg and 5mg/kg protected more than 2/3s of the mice. All three dose levels reduced bacterial loads in blood and peritoneal fluid by 10-fold or more when counted six hours after bacterial challenge. We determined that DAN2 acts by compromising the integrity of the E. coli membrane. This study supports the potential of DAN2 peptide as a therapeutic agent for treating antibiotic resistant Gram-negative bacterial infections.

Enhanced Silkworm Cecropin B Antimicrobial Activity against Pseudomonas aeruginosa from Single Amino Acid Variation

Pseudomonas aeruginosa is an opportunistic bacterial pathogen causing severe infections in hospitalized and immunosuppressed patients, particularly individuals affected by cystic fibrosis. Several clinically isolated P. aeruginosa strains were found to be resistant to three or more antimicrobial classes indicating the importance of identifying new antimicrobials active against this pathogen. Here, we characterized the antimicrobial activity and the action mechanisms against P. aeruginosa of two natural isoforms of the antimicrobial peptide cecropin B, both isolated from the silkworm Bombyx mori. These cecropin B isoforms differ in a single amino acid substitution within the active portion of the peptide, so that the glutamic acid of the E53 CecB variant is replaced by a glutamine in the Q53 CecB isoform. Both peptides showed a high antimicrobial and membranolytic activity against P. aeruginosa, with Q53 CecB displaying greater activity compared with the E53 CecB isoform. Biophysical analyses, live-cell NMR, and molecular-dynamic-simulation studies indicated that both peptides might act as membrane-interacting elements, which can disrupt outer-membrane organization, facilitating their translocation toward the inner membrane of the bacterial cell. Our data also suggest that the amino acid variation of the Q53 CecB isoform represents a critical factor in stabilizing the hydrophobic segment that interacts with the bacterial membrane, determining the highest antimicrobial activity of the whole peptide. Its high stability to pH and temperature variations, tolerance to high salt concentrations, and low toxicity against human cells make Q53 CecB a promising candidate in the development of CecB-derived compounds against P. aeruginosa.

In Vitro and In Vivo Antimalarial Activity of LZ1, a Peptide Derived from Snake Cathelicidin

Antimalarial drug resistance is an enormous global threat. Recently, antimicrobial peptides (AMPs) are emerging as a new source of antimalarials. In this study, an AMP LZ1 derived from snake cathelicidin was identified with antimalarial activity. In the in vitro antiplasmodial assay, LZ1 showed strong suppression of blood stage Plasmodium falciparum (P. falciparum) with an IC50 value of 3.045 μM. In the in vivo antiplasmodial assay, LZ1 exerted a significant antimalarial activity against Plasmodium berghei (P. berghei) in a dose- and a time- dependent manner. In addition, LZ1 exhibited anti-inflammatory effects and attenuated liver-function impairment during P. berghei infection. Furthermore, by employing inhibitors against glycolysis and oxidative phosphorylation in erythrocytes, LZ1 specifically inhibited adenosine triphosphate (ATP) production in parasite-infected erythrocyte by selectively inhibiting the pyruvate kinase activity. In conclusion, the present study demonstrates that LZ1 is a potential candidate for novel antimalarials development.

Hermetia illucens larvae as a potential dietary protein source altered the microbiota and modulated mucosal immune status in the colon of finishing pigs

Background

Insects, such as Hermetia illucens larvae, are rich in chitin and proteins, and represent a suitable feed ingredient replacement for animals. However, little is known about the effect of administering H. illucens larvae on intestinal microbiota, bacterial metabolite profiles, and mucosal immune status in animals. This study aimed to investigate the effects of administering H. illucens larvae on colonic microbiota and bacterial metabolites production in finishing pigs. Seventy-two crossbred (Duroc × Landrace × Large White) female pigs (initial body weight, 76.0 ± 0.52 kg) were randomly allocated to three different dietary treatments: a control diet (Control group) and two diets corresponding to 4% (H1 group) and 8% (H2 group) H. illucens larvae inclusion levels, respectively. Each treatment consisted of eight pens (replicates), with three pigs per pen. After 46 days of feeding, eight pigs per treatment (n = 8) were slaughtered, and the colonic digesta and mucosa were collected for microbial composition and microbial fermentation products, and genes expression analyses.

Results

The results showed that the H1 diet significantly increased the abundance of Lactobacillus, Pseudobutyrivibrio, Roseburia, and Faecalibacterium compared with those in the control group (P < 0.05), with a decrease in the abundance of Streptococcus. The numbers of Lactobacillus, Roseburia, and Clostridium cluster XIVa were significantly greater in the H1 group than in the control group (P < 0.05). Meanwhile, H2 diet increased the number of Clostridium cluster XIVa compared with the control group (P < 0.05). For colonic metabolites, total short chain fatty acids, butyrate, and isobutyrate concentrations were significantly higher in the H1 group than those in the control group (P < 0.05); the H1 treatment caused a striking decrease in protein fermentation compared with the control group, as the concentrations of total amines, cadaverine, tryptamine, phenol, p-cresol, and skatole were significantly lower (P < 0.05). Additionally, H2 diet also increased butyrate concentration compared with control group (P < 0.05), while decreased the concentrations of phenol, p-cresol, and skatole (P < 0.05). Pigs in the H1 group down-regulated the expression of TLR-4 and pro-inflammatory cytokines (IFN-γ) compared with pigs in the control group (P < 0.05), and up-regulated anti-inflammatory cytokine (IL-10) and intestinal barrier genes (ZO-1, occludin, and mucin-1). H2 diet up-regulated the expression of ZO-1 compared with control group (P < 0.05). Furthermore, the changes in the colonic mucosal gene expression were associated with changes in the bacterial composition and their metabolites.

Conclusions

Collectively, dietary inclusion of Hermetia illucens larvae may enhance mucosal immune homeostasis of pigs via altering bacterial composition and their metabolites. These findings provide a new perspective on insect meal as a sustainable protein source rich in nutrient ingredients for swine.

Electronic supplementary material

The online version of this article (10.1186/s40104-019-0358-1) contains supplementary material, which is available to authorized users.

Repurposing of Glycine-Rich Proteins in Abiotic and Biotic Stresses in the Lone-Star Tick (Amblyomma americanum)

Tick feeding requires the secretion of a huge number of pharmacologically dynamic proteins and other molecules which are vital for the formation of the cement cone, the establishment of the blood pool and to counter against the host immune response. Glycine-rich proteins (GRP) are found in many organisms and can function in a variety of cellular processes and structures. The functional characterization of the GRPs in the tick salivary glands has not been elucidated. GRPs have been found to play a role in the formation of the cement cone; however, new evidence suggests repurposing of GRPs in the tick physiology. In this study, an RNA interference approach was utilized to silence two glycine-rich protein genes expressed in early phase of tick feeding to determine their functional role in tick hematophagy, cement cone structure, and microbial homeostasis within the tick host. Additionally, the transcriptional regulation of GRPs was determined after exposure to biotic and abiotic stresses including cold and hot temperature, injury, and oxidative stress. This caused a significant up-regulation of AamerSigP-34358, Aam-40766, AamerSigP-39259, and Aam-36909. Our results suggest ticks repurpose these proteins and further functional characterization of GRPs may help to design novel molecular strategies to disrupt the homeostasis and the pathogen transmission.

The effect of Wolbachia on gene expression in Drosophila paulistorum and its implications for symbiont-induced host speciation

Background

The Neotropical fruit fly Drosophila paulistorum (Diptera: Drosophilidae) is a species complex in statu nascendi comprising six reproductively isolated semispecies, each harboring mutualistic Wolbachia strains. Although wild type flies of each semispecies are isolated from the others by both pre- and postmating incompatibilities, mating between semispecies and successful offspring development can be achieved once flies are treated with antibiotics to reduce Wolbachia titer. Here we use RNA-seq to study the impact of Wolbachia on D. paulistorum and investigate the hypothesis that the symbiont may play a role in host speciation. For that goal, we analyze samples of heads and abdomens of both sexes of the Amazonian, Centro American and Orinocan semispecies of D. paulistorum.

Results

We identify between 175 and 1192 differentially expressed genes associated with a variety of biological processes that respond either globally or according to tissue, sex or condition in the three semispecies. Some of the functions associated with differentially expressed genes are known to be affected by Wolbachia in other species, such as metabolism and immunity, whereas others represent putative novel phenotypes involving muscular functions, pheromone signaling, and visual perception.

Conclusions

Our results show that Wolbachia affect a large number of biological functions in D. paulistorum, particularly when present in high titer. We suggest that the significant metabolic impact of the infection on the host may cause several of the other putative and observed phenotypes. We also speculate that the observed differential expression of genes associated with chemical communication and reproduction may be associated with the emergence of pre- and postmating barriers between semispecies, which supports a role for Wolbachia in the speciation of D. paulistorum.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5816-9) contains supplementary material, which is available to authorized users.

Ingestion of killed bacteria activates antimicrobial peptide genes in Drosophila melanogaster and protects flies from septic infection

Drosophila melanogaster possesses a sophisticated and effective immune system composed of humoral and cellular immune responses, and production of antimicrobial peptides (AMPs) is an important defense mechanism. Expression of AMPs is regulated by the Toll and IMD (immune deficiency) pathways. Production of AMPs can be systemic in the fat body or a local event in the midgut and epithelium. So far, most studies focus on systemic septic infection in adult flies and little is known about AMP gene activation after ingestion of killed bacteria. In this study, we investigated activation of AMP genes in the wild-type w¹¹¹⁸, MyD88 and Imd mutant flies after ingestion of heat-killed Escherichia coli and Staphylococcus aureus. We showed that ingestion of E. coli activated most AMP genes, including drosomycin and diptericin, in the first to third instar larvae and pupae, while ingestion of S. aureus induced only some AMP genes in some larval stages or in pupae. In adult flies, ingestion of killed bacteria activated AMP genes differently in males and females. Interestingly, ingestion of killed E. coli and S. aureus in females conferred resistance to septic infection by both live pathogenic Enterococcus faecalis and Pseudomonas aeruginosa, and ingestion of E. coli in males conferred resistance to P. aeruginosa infection. Our results indicated that E. coli and S. aureus can activate both the Toll and IMD pathways, and systemic and local immune responses work together to provide Drosophila more effective protection against infection.

Sarconesin II, a New Antimicrobial Peptide Isolated from Sarconesiopsis magellanica Excretions and Secretions

Antibiotic resistance is at dangerous levels and increasing worldwide. The search for new antimicrobial drugs to counteract this problem is a priority for health institutions and organizations, both globally and in individual countries. Sarconesiopsis magellanica blowfly larval excretions and secretions (ES) are an important source for isolating antimicrobial peptides (AMPs). This study aims to identify and characterize a new S. magellanica AMP. RP-HPLC was used to fractionate ES, using C18 columns, and their antimicrobial activity was evaluated. The peptide sequence of the fraction collected at 43.7 min was determined by mass spectrometry (MS). Fluorescence and electronic microscopy were used to evaluate the mechanism of action. Toxicity was tested on HeLa cells and human erythrocytes; physicochemical properties were evaluated. The molecule in the ES was characterized as sarconesin II and it showed activity against Gram-negative (Escherichia coli MG1655, Pseudomonas aeruginosa ATCC 27853, P. aeruginosa PA14) and Gram-positive (Staphylococcus aureus ATCC 29213, Micrococcus luteus A270) bacteria. The lowest minimum inhibitory concentration obtained was 1.9 μM for M. luteus A270; the AMP had no toxicity in any cells tested here and its action in bacterial membrane and DNA was confirmed. Sarconesin II was documented as a conserved domain of the ATP synthase protein belonging to the Fli-1 superfamily. The data reported here indicated that peptides could be alternative therapeutic candidates for use in infections against Gram-negative and Gram-positive bacteria and eventually as a new resource of compounds for combating multidrug-resistant bacteria.

Toll family members bind multiple Spätzle proteins and activate antimicrobial peptide gene expression in Drosophila

The Toll signaling pathway in Drosophila melanogaster regulates several immune-related functions, including the expression of antimicrobial peptide (AMP) genes. The canonical Toll receptor (Toll-1) is activated by the cytokine Spätzle (Spz-1), but Drosophila encodes eight other Toll genes and five other Spz genes whose interactions with one another and associated functions are less well-understood. Here, we conducted in vitro assays in the Drosophila S2 cell line with the Toll/interleukin-1 receptor (TIR) homology domains of each Toll family member to determine whether they can activate a known target of Toll-1, the promoter of the antifungal peptide gene drosomycin. All TIR family members activated the drosomycin promoter, with Toll-1 and Toll-7 TIRs producing the highest activation. We found that the Toll-1 and Toll-7 ectodomains bind Spz-1, -2, and -5, and also vesicular stomatitis virus (VSV) virions, and that Spz-1, -2, -5, and VSV all activated the promoters of drosomycin and several other AMP genes in S2 cells expressing full-length Toll-1 or Toll-7. In vivo experiments indicated that Toll-1 and Toll-7 mutants could be systemically infected with two bacterial species (Enterococcus faecalis and Pseudomonas aeruginosa), the opportunistic fungal pathogen Candida albicans, and VSV with different survival times in adult females and males compared with WT fly survival. Our results suggest that all Toll family members can activate several AMP genes. Our results further indicate that Toll-1 and Toll-7 bind multiple Spz proteins and also VSV, but they differentially affect adult survival after systemic infection, potentially because of sex-specific differences in Toll-1 and Toll-7 expression.

Insect anionic septapeptides suppress DENV replication by activating antiviral cytokines and miRNAs in primary human monocytes

Dengue viruses (DENVs) have threatened 2/3 of the world population for decades. Thus, combating DENV infection with either antiviral therapy or protective vaccination is an urgent goal. In the present study, we investigated the anti-DENV activity of insect cell-derived anionic septapeptides from C6/36 mosquito cell cultures persistently infected with DENV. These molecules were previously shown to protect C6/36 and Vero cells against DENV infection. We found that treatment with these septapeptides strongly and rapidly downregulated the multiplication of DENV-1 16007, DENV-3 16562, and DENV-4 1036 but not that of DENV-2 16681 in primary human monocytes. This inhibitory effect was likely mediated through various routes including the increased production of antiviral cytokines (IFN-I), activation of mononuclear cell migration, and upregulation of the expression of antiviral miRNAs (has-miR-30e*, has-miR-133a, and has-miR-223) and inflammation-related miRNAs (has-miR-146a and has-miR-147). In conclusion, anionic septapeptides exerted anti-DENV activity in human monocytes through the upregulation of innate immune responses and the activation of several previously reported antiviral and inflammation-related miRNAs.

Innate humoral immune defences in mammals and insects: The same, with differences ?

The insect immune response demonstrates many similarities to the innate immune response of mammals and a wide range of insects is now employed to assess the virulence of pathogens and produce results comparable to those obtained using mammals. Many of the humoral responses in insects and mammals are similar (e.g. insect transglutaminases and human clotting factor XIIIa) however a number show distinct differences. For example in mammals, melanization plays a role in protection from solar radiation and in skin and hair pigmentation. In contrast, insect melanization acts as a defence mechanism in which the proPO system is activated upon pathogen invasion. Human and insect antimicrobial peptides share distinct structural and functional similarities, insects produce the majority of their AMPs from the fat body while mammals rely on production locally at the site of infection by epithelial/mucosal cells. Understanding the structure and function of the insect immune system and the similarities with the innate immune response of mammals will increase the attractiveness of using insects as in vivo models for studying host – pathogen interactions.