The discovery and analysis of a diverged family of novel antifungal moricin-like peptides in the wax moth Galleria mellonella

Peptides from Galleria mellonella against Cryptococcus spp: toxicity in three-dimensional cell cultures and G. mellonella

Aim: This work aimed to test peptides against the planktonic and biofilm form of Cryptococcus spp. and in vitro toxicity using three-dimensional (3D) cells characterized and evaluate in vivo toxicity in Galleria mellonella.Materials & methods: Susceptibility tests were conducted on the planktonic form and biofilm formation. The toxicity of the peptides was evaluated in lung and brain cells in monolayer (2D) and 3D mono- and co-culture, in addition to in vivo analysis with G. mellonella.Results: Susceptibility values ranged from 31.25 to over 250 µg/ml with a fungicidal profile. Regarding toxicity, the PepM2 peptide was not toxic in 3D culture (500 µg/ml). G. mellonella, showed a survival rate of more than 85% In assays with brain and lung cell lines, concentrations ranged from 4 × 104 to 4 × 103 cells/well for brain cells and 1 × 103 cells/well for lung cells. Cocultures used 1 × 105 brain and 1 × 103 lung cells.Conclusion: This study shows that the peptides have great potential against cryptococcosis, and all spheroids were characterized as having a spheroidal and compact structure.

Dietary Black Soldier Fly (Hermetia illucens)-Dipterose-BSF-Enhanced Zebrafish Innate Immunity Gene Expression and Resistance to Edwardsiella tarda Infection

Dietary management using immunostimulants to protect fish health and prevent bacterial infection is widely practiced. Many insect species possess various bioactive substances that can improve animal health. We previously identified several bioactive polysaccharides derived from insects, including dipterose-BSF from black soldier fly (Hermetia illucens) larvae; this can stimulate innate immunity in mammalian macrophage RAW264.7 cells. However, the effect of dietary dipterose-BSF on the immune system of teleosts remains unclear. Here, we analyzed the immune status of zebrafish (Danio rerio) after 14 days of dietary inclusion of dipterose-BSF (0.01, 0.1, and 1 µg/g), followed by an immersion challenge using Edwardsiella tarda. To identify changes in the transcriptional profile induced by dipterose-BSF, we performed RNA-sequencing analyses of the liver and intestine. Differentially expressed genes were investigated, with both organs showing several upregulated genes, dominated by nuclear factor and tumor necrosis factor family genes. Gene Ontology analysis revealed several terms were significantly higher in the experimental group compared with the control group. Challenge tests suggested that dietary dipterose-BSF had some positive effects on disease resistance in fish, but these effects were not pronounced.

Antimicrobial activity of lipids extracted from Hermetia illucens reared on different substrates

As the problem of antimicrobial resistance is constantly increasing, there is a renewed interest in antimicrobial products derived from natural sources, particularly obtained from innovative and eco-friendly materials. Insect lipids, due to their fatty acid composition, can be classified as natural antimicrobial compounds. In order to assess the antibacterial efficacy of Hermetia illucens lipids, we extracted this component from the larval stage, fed on different substrates and we characterized it. Moreover, we analyzed the fatty acid composition of the feeding substrate, to determine if and how it could affect the antimicrobial activity of the lipid component. The antimicrobial activity was evaluated against Gram-positive Micrococcus flavus and Gram-negative bacteria Escherichia coli. Analyzing the fatty acid profiles of larval lipids that showed activity against the two bacterial strains, we detected significant differences for C4:0, C10:0, C16:1, C18:3 n3 (ALA), and C20:1. The strongest antimicrobial activity was verified against Micrococcus flavus by lipids extracted from larvae reared on strawberry, tangerine, and fresh manure substrates, with growth inhibition zones ranged from 1.38 to 1.51 mm, while only the rearing on manure showed the effect against Escherichia coli. Notably, the fatty acid profile of H. illucens seems to not be really influenced by the substrate fatty acid profile, except for C18:0 and C18:2 CIS n6 (LA). This implies that other factors, such as the rearing conditions, larval development stages, and other nutrients such as carbohydrates, affect the amount of fatty acids in insects. KEY POINTS: • Feeding substrates influence larval lipids and fatty acids (FA) • Generally, there is no direct correlation between substrate FAs and the same larvae FAs • Specific FAs influence more the antimicrobial effect of BSF lipids.

Homologs of bacterial heat-labile enterotoxin subunit A contribute to development, stress response, and virulence in filamentous entomopathogenic fungus Beauveria bassiana

Introduction

Enterotoxigenic bacteria commonly excrete heat-labile enterotoxins (LT) as virulence factors that consist of one subunit A (LTA) and five B subunits (LTB). In fungi, there are a large number of genes encoding the homologs of LTA, but their biological roles remain largely unknown.

Methods

In this study, we identified 14 enterotoxin_A domain proteins in filamentous fungus B. bassiana in which five proteins were functionally characterized.

Results

Five proteins displayed diverse sub-cellular localizations but perform convergent functions in stress response, development, and virulence. The loss of five LTA genes resulted in significant reduction in conidial production, blastospore formation, and the increased sensitivity to oxidative and cell wall -perturbing stresses. The virulence of five disruptants was notably weakened as indicated by topical and intrahemocoel injection assays. Notably, the loss of these five proteins led to the significant changes in the carbohydrate profiles of cellular surface, which induced the enhanced host immune reactions of encapsulation and melanization.

Discussion

Thus, LTA proteins contribute to the fungus-host interaction via maintaining the carbohydrate profiles of cellular surface. This study expands our understanding of the enterotoxin_A domain proteins in fungal physiology and deepens mechanisms involved in the lifestyle of fungal insect pathogens.

Insect-pathogen crosstalk and the cellular-molecular mechanisms of insect immunity: uncovering the underlying signaling pathways and immune regulatory function of non-coding RNAs

Multicellular organisms are constantly subjected to pathogens that might be harmful. Although insects lack an adaptive immune system, they possess highly effective anti-infective mechanisms. Bacterial phagocytosis and parasite encapsulation are some forms of cellular responses. Insects often defend themselves against infections through a humoral response. This phenomenon includes the secretion of antimicrobial peptides into the hemolymph. Specific receptors for detecting infection are required for the recognition of foreign pathogens such as the proteins that recognize glucans and peptidoglycans, together referred to as PGRPs and βGRPs. Activation of these receptors leads to the stimulation of signaling pathways which further activates the genes encoding for antimicrobial peptides. Some instances of such pathways are the JAK-STAT, Imd, and Toll. The host immune response that frequently accompanies infections has, however, been circumvented by diseases, which may have assisted insects evolve their own complicated immune systems. The role of ncRNAs in insect immunology has been discussed in several notable studies and reviews. This paper examines the most recent research on the immune regulatory function of ncRNAs during insect-pathogen crosstalk, including insect- and pathogen-encoded miRNAs and lncRNAs, and provides an overview of the important insect signaling pathways and effector mechanisms activated by diverse pathogen invaders.

The Virtuous Galleria mellonella Model for Scientific Experimentation

The first research on the insect Galleria mellonella was published 85 years ago, and the larva is now widely used as a model to study infections caused by bacterial and fungal pathogens, for screening new antimicrobials, to study the adjacent immune response in co-infections or in host-pathogen interaction, as well as in a toxicity model. The immune system of the G. mellonella model shows remarkable similarities with mammals. Furthermore, results from G. mellonella correlate positively with mammalian models and with other invertebrate models. Unlike other invertebrate models, G. mellonella can withstand temperatures of 37 °C, and its handling and experimental procedures are simpler. Despite having some disadvantages, G. mellonella is a virtuous in vivo model to be used in preclinical studies, as an intermediate model between in vitro and mammalian in vivo studies, and is a great example on how to apply the bioethics principle of the 3Rs (Replacement, Reduction, and Refinement) in animal experimentation. This review aims to discuss the progress of the G. mellonella model, highlighting the key aspects of its use, including experimental design considerations and the necessity to standardize them. A different score in the "cocoon" category included in the G. mellonella Health Index Scoring System is also proposed.

Cationic protein 8 plays multiple roles in Galleria mellonella immunity

Galleria mellonella cationic protein 8 (GmCP8) is a hemolymph protein previously identified as an opsonin and an inhibitor of fungal proteases. In this work, we showed its bactericidal activity toward Pseudomonas entomophila, Pseudomonas aeruginosa, Bacillus thuringiensis, Staphylococcus aureus, and Escherichia coli and against yeast-like fungi Candida albicans. The activity against E. coli was correlated with bacterial membrane permeabilization. In turn, in the case of P. entomophila, B. thuringiensis, and C. albicans, the atomic force microscopy analysis of the microbial surface showed changes in the topography of cells and changes in their nanomechanical properties. GmCP8 also showed the inhibitory activity toward the serine protease trypsin and the metalloproteinase thermolysin. The expression of the gene encoding the GmCP8 protein did not increase either in the gut or in the fat body of G. mellonella after oral infection with P. entomophila. Similarly, the amount of GmCP8 in the hemolymph of G. mellonella did not change in immune-challenged insects. However, when GmCP8 was injected into the G. mellonella hemocel, a change in the survival curve was observed in the infected larvae. Our results shed new light on the function of GmCP8 protein in insect immunity, indicating its role in humoral defence mechanisms.

The Entomopathogenic Fungus Beauveria bassiana Shows Its Toxic Side within Insects: Expression of Genes Encoding Secondary Metabolites during Pathogenesis

Entomopathogenic fungi are extensively used for the control of insect pests worldwide. Among them, Beauveria bassiana (Ascomycota: Hypocreales) produce a plethora of toxic secondary metabolites that either facilitate fungal invasion or act as immunosuppressive compounds. These toxins have different chemical natures, such as nonribosomal peptides and polyketides. Even though their precise role is poorly understood, they are usually linked to virulence. These fungal secondary metabolites are produced by the expression of gene clusters encoding the various proteins needed for their biosynthesis. Each cluster includes synthetases for nonribosomal peptides (NRPS), polyketides (PKS), or hybrid NRPS–PKS genes. The aim of this review is to summarize the information available from transcriptomics and quantitative PCR studies related to the expression of B. bassiana NRPS and PKS genes inside different insects as the infection progresses; as for the host immune response, to help understand the mechanisms that these toxins trigger as virulence factors, antimicrobials, or immunosuppressives within the context of a fungus–insect interaction.

Fungal α-1,3-Glucan as a New Pathogen-Associated Molecular Pattern in the Insect Model Host Galleria mellonella

Recognition of pathogen-associated molecular patterns (PAMPs) by appropriate pattern recognition receptors (PRRs) is a key step in activating the host immune response. The role of a fungal PAMP is attributed to β-1,3-glucan. The role of α-1,3-glucan, another fungal cell wall polysaccharide, in modulating the host immune response is not clear. This work investigates the potential of α-1,3-glucan as a fungal PAMP by analyzing the humoral immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan. We demonstrated that 57-kDa and 61-kDa hemolymph proteins, identified as β-1,3-glucan recognition proteins, bound to A. niger α-1,3-glucan. Other hemolymph proteins, i.e., apolipophorin I, apolipophorin II, prophenoloxidase, phenoloxidase activating factor, arylphorin, and serine protease, were also identified among α-1,3-glucan-interacting proteins. In response to α-1,3-glucan, a 4.5-fold and 3-fold increase in the gene expression of antifungal peptides galiomicin and gallerimycin was demonstrated, respectively. The significant increase in the level of five defense peptides, including galiomicin, corresponded well with the highest antifungal activity in hemolymph. Our results indicate that A. niger α-1,3-glucan is recognized by the insect immune system, and immune response is triggered by this cell wall component. Thus, the role of a fungal PAMP for α-1,3-glucan can be postulated.

Transcriptomic analyses reveal comprehensive responses of insect hemocytes to mycopathogen Beauveria bassiana, and fungal virulence-related cell wall protein assists pathogen to evade host cellular defense

Entomopathogenic fungi naturally infect insect hosts in environment. Fungal invasion and host immune defense are still in the progress of co-evolution. In this study, entomopathogenic fungus Beauveria bassiana and lepidopteran insect Galleria mellonella were used to investigate host cellular immunity and fungal strategy to evade host defense. First of all, genome-wide expression revealed the transcriptomic responses of hemocytes to insect mycopathogen, which dynamically varied during infection process. Enrichment analysis indicated that differentially expressed genes were primarily involved in metabolism, cellular process and immune system. Notably, cellular response involved a series of hydrolytic enzyme and antimicrobial peptide genes which were sorted together in clustering analysis. In B. bassiana, a cell-wall protein gene (BbCwp) contributes to fungal development in host hemocoel and virulence. RT-qPCR analyses indicated that infection by ΔBbCwp mutant strain caused the up-regulated expression of a series of immunity-related genes, including β-1, 3-glucan recognition protein, hydrolytic enzyme and antimicrobial peptide genes. Disruption of BbCwp resulted in a significant change in conidial lectin-binding feature and the enhanced encapsulation by the host hemocytes. After being treated with hydrolytic enzymes, ΔBbCwp mutant displayed a significantly enhanced sensitivity to osmotic and oxidative stresses. In conclusion, fungal invasion initiates comprehensive physiological responses in the host hemocytes. For mycopathogen, cell-wall protein plays an important role in fungal evasion of immunity defense and colonization in host. Our studies provide an initial framework for exploring more mechanistic details about the fungus–host interaction.

Activity of Anti-Microbial Peptides (AMPs) against Leishmania and Other Parasites: An Overview

Anti-microbial peptides (AMPs), small biologically active molecules, produced by different organisms through their innate immune system, have become a considerable subject of interest in the request of novel therapeutics. Most of these peptides are cationic-amphipathic, exhibiting two main mechanisms of action, direct lysis and by modulating the immunity. The most commonly reported activity of AMPs is their anti-bacterial effects, although other effects, such as anti-fungal, anti-viral, and anti-parasitic, as well as anti-tumor mechanisms of action have also been described. Their anti-parasitic effect against leishmaniasis has been studied. Leishmaniasis is a neglected tropical disease. Currently among parasitic diseases, it is the second most threating illness after malaria. Clinical treatments, mainly antimonial derivatives, are related to drug resistance and some undesirable effects. Therefore, the development of new therapeutic agents has become a priority, and AMPs constitute a promising alternative. In this work, we describe the principal families of AMPs (melittin, cecropin, cathelicidin, defensin, magainin, temporin, dermaseptin, eumenitin, and histatin) exhibiting a potential anti-leishmanial activity, as well as their effectiveness against other microorganisms.

A comparison of the production of antimicrobial peptides and proteins by Galleria mellonella larvae in response to infection with two Pseudomonas aeruginosa strains differing in the profile of secreted proteases

The work presents identification of antimicrobial peptides and proteins (AMPs) in the hemolymph of Galleria mellonella larvae infected with two Pseudomonas aeruginosa strains (ATCC 27,853 and PA18), differing in the profile of secreted proteases. The insects were immunized with bacteria cultivated in rich (LB) and minimal (M9) media, which resulted in appearance of a similar broad set of AMPs in the hemolymph. Among them, 13 peptides and proteins were identified, i.e. proline-rich peptides 1 and 2, lebocin-like anionic peptide 1 and anionic peptide 2, defensin/galiomicin, cecropin, cecropin D-like peptide, apolipophoricin, gallerimycin, moricin-like peptide B, lysozyme, apolipophorin III, and superoxide dismutase. Bacterial strain- and/or medium-dependent changes in the level of proline-rich peptide 1, anionic peptide 1 and 2, moricin-like peptide B, cecropin D-like and gallerimycin were observed. The analysis of the expression of genes encoding cecropin, gallerimycin, and galiomicin indicated that they were differently affected by the bacterial strain but mainly by the medium used for bacterial culture. The highest expression was found for the LB medium. In addition to the antibacterial and antifungal activity, proteolytic activity was detected in the hemolymph of the P. aeruginosa-infected insects. Based on these results and those presented in our previous reports, it can be postulated that the appearance of AMPs in G. mellonella hemolymph can be triggered not only by P. aeruginosa pathogen associated molecular patterns (PAMPs) but also by bacterial extracellular proteases secreted during infection. However, although there were no qualitative differences in the set of AMPs depending on the P. aeruginosa strain and medium, differences in the level of particular AMPs synthesized in response to the bacteria used were observed.

Proteomic profiling of bacterial and fungal induced immune priming in Galleria mellonella larvae

Some insects display immunological priming as a result of elevated humoral and cellular responses which give enhanced survival against subsequent infection. The humoral immune response of Galleria mellonella larvae following pre-exposure to heat killed Staphylococcus aureus or Candida albicans cells was determined by quantitative mass spectrometry in order to assess the relationship between the humoral immune response and resistance to subsequent bacterial or fungal infection. Larvae pre-exposed to heat killed S. aureus showed increased resistance to subsequent bacterial and fungal infection. Larvae displayed an increased hemocyte density (14.08 ± 2.14 × 10⁶ larva^-1 (p < 0.05) compared to the PBS injected control [10.41 ± 1.67 × 10⁶ larva^-1]) and increased abundance of antimicrobial proteins (cecropin-D-like peptide (+22.23 fold), hdd11 (+12.61 fold) and prophenol oxidase activating enzyme 3 (+5.96 fold) in response to heat killed S. aureus. Larvae pre-exposed to heat killed C. albicans cells were resistant to subsequent fungal infection but not bacterial infection and showed a reduced hemocyte density (6.01 ± 1.63 × 10⁶ larva^-1 (p < 0.01) and increased abundance of hdd11 (+32.73 fold) and moricin-like peptide C1 (+16.76 fold). While immune priming is well recognised in G. mellonella larvae the results presented here indicate distinct differences in the response of larvae following exposure to heat killed bacterial and fungal cells.

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.

Proteomic analysis of the processes leading to Madurella mycetomatis grain formation in Galleria mellonella larvae

Mycetoma is a neglected chronic and granulomatous infection primarily associated with the fungal pathogen Madurella mycetomatis. Characteristic of this infection is the formation of grains. However, the processes leading to grain formation are not known. In this study, we employed a proteomic approach to characterise M. mycetomatis grain formation in Galleria mellonella larvae and map the processes leading to grain formation over time. For this, at 1 day, 3 days and 7 days post-inoculation, proteins from grains and hemolymph were extracted and analysed by label-free mass spectrometry. A total of 87, 51 and 48 M. mycetomatis proteins and 713, 997, 18 G. mellonella proteins were found in grains on day 1, 3 and 7 post-inoculation respectively. M. mycetomatis proteins were mainly involved in cellular metabolic processes and numerous enzymes were encountered. G. mellonella proteins were primarily involved in the nodulation process. The proteins identified were linked to nodulation and grain formation and four steps of grain formation were identified. The results of this proteomic approach could in the future be used to design novel strategies to interfere with mycetoma grain formation and to combat this difficult to treat infection.

Although grain formation is the hallmark of mycetoma, so far the pathways leading to grain formation were not studied. Since our hypothesis is that both host and pathogen play a role in this process, we aimed to study this process in a model system. Grains can be formed in the invertebrate Galleria mellonella and different stages of grain formation can be noted within the larvae. We therefore infected G. mellonella with the mycetoma causative agent Madurella mycetomatis, and monitored grain formation over time. At day 1, day 3 and day 7 post-inoculation, grains and hemolymph were obtained from infected larvae. Proteins were isolated and identified by label-free mass spectrometry. By analyzing the proteins found in both host and pathogen on the different time points, we were able to develop a grain model over time. This grain model can in the future be used to identify novel treatments for this difficult to treat infection.

Candida albicans increases the pathogenicity of Staphylococcus aureus during polymicrobial infection of Galleria mellonella larvae

This study detailed the responses of Galleria mellonella larvae to disseminated infection caused by co-infection with Candida albicans and Staphylococcus aureus. Doses of C. albicans (1×10⁵ larva^-1) and S. aureus (1×10⁴ larva^-1) were non-lethal in mono-infection but when combined significantly (P<0.05) reduced larval survival at 24, 48 and 72 h relative to larvae receiving S. aureus (2×10⁴ larva^-1) alone. Co-infected larvae displayed a significantly higher density of S. aureus larva^-1 compared to larvae infected solely with S. aureus. Co-infection resulted in dissemination throughout the host and the appearance of large nodules. Co-infection of larvae with C. albicans and S. aureus (2×10⁴ larva^-1) resulted in an increase in the density of circulating haemocytes compared to that in larvae infected with only S. aureus. Proteomic analysis of co-infected larval haemolymph revealed increased abundance of proteins associated with immune responses to bacterial and fungal infection such as cecropin-A (+45.4-fold), recognition proteins [e.g. peptidoglycan-recognition protein LB (+14-fold)] and proteins associated with nodule formation [e.g. Hdd11 (+33.3-fold)]. A range of proteins were also decreased in abundance following co-infection, including apolipophorin (-62.4-fold), alpha-esterase 45 (-7.7-fold) and serine proteinase (-6.2-fold). Co-infection of larvae resulted in enhanced proliferation of S. aureus compared to mono-infection and an immune response showing many similarities to the innate immune response of mammals to infection. The utility of G. mellonella larvae for studying polymicrobial infection is highlighted.

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.

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.

Host-pathogen interactions upon the first and subsequent infection of Galleria mellonella with Candida albicans

Insects are able to develop enhanced resistance in response to repeated infection. This phenomenon is called immune priming. In this work, so-called "primed" Galleria mellonella larvae were re-infected with a lethal dose of Candida albicans 48 h after injection of a non-lethal dose, while "non-primed" larvae were infected only with a lethal dose. The increased resistance of the primed larvae correlated with a slower rate of body colonisation by the fungus. Changes in the protein profiles were detected in the whole hemolymph of the primed insects. The analysis of low-molecular weight proteins and peptides obtained with the use of three different organic solvents and comparative quantitative HPLC analysis thereof showed that the primed larvae did not have higher amounts of any infection-inducible polypeptides than the non-primed larvae. Moreover, electrophoresis of low-molecular weight polypeptides revealed an even lower level of immune-induced peptides in the primed larvae than in the non-primed ones. Furthermore, the defence activity of larval hemolymph, i.e. the antifungal, antibacterial, and lysozyme-type activity, was up-regulated in the primed larvae at the time of re-infection and, consequently, at the early time points after the infection with the lethal dose. Twenty four hours after the infection, these parameters were equally high in the non-primed and primed larvae. Accordingly, at the time of the injection of the lethal dose, certain immune-inducible genes were up-regulated. However, 24 h after the infection with the lethal dose, their expression in both groups was incomparably higher than at the time of the infection and, in most cases, it was as high in the primed larvae as in the non-primed ones. We found that only anti yeast-like activity was enhanced 24 h after the re-infection. This correlated with results obtained by testing the priming effect in heterologous systems: the primed animals did not exhibit higher resistance to the other pathogens tested.

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.

A powerful in vivo alternative model in scientific research: Galleria mellonella

Murine models are suggested as the gold standard for scientific research, but they have many limitations of ethical and logistical concern. Then, the alternative host models have been developed to use in many aspects especially in invertebrate animals. These models are selected for many areas of research including genetics, physiology, biochemistry, evolution, disease, neurobiology, and behavior. During the past decade, Galleria mellonella has been used for several medical and scientific researches focusing on human pathogens. This model commonly used their larvae stage due to their easy to use, non-essential special tools or special technique, inexpensive, short life span, and no specific ethical requirement. Moreover, their innate immune response close similarly to mammals, which correlate with murine immunity. In this review, not only the current knowledge of characteristics and immune response of G. mellonella, and the practical use of these larvae in medical mycology research have been presented, but also the better understanding of their limitations has been provided.

Proteomic Analysis of the Responses of Candida albicans during Infection of Galleria mellonella Larvae

This study assessed the development of disseminated candidiasis within Galleria mellonella larvae and characterized the proteomic responses of Candida albicans to larval hemolymph. Infection of larvae with an inoculum of 1 × 10⁶ yeast cells reduced larval viability 24 (53.33 ± 3.33%), 48 (33.33 ± 3.33%) and 72 (6.66 ± 3.33%) h post infection. C. albicans infection quickly disseminated from the site of inoculation and the presence of yeast and hyphal forms were found in nodules extracted from infected larvae at 6 and 24 h. A range of proteins secreted during infection of G. mellonella by C. albicans were detected in larval hemolymph and these were enriched for biological processes such as interaction with host and pathogenesis. The candicidal activity of hemolymph after immediate incubation of yeast cells resulted in a decrease in yeast cell viability (0.23 ± 0.03 × 10⁶ yeast cells/mL), p < 0.05) as compared to control (0.99 ± 0.01 × 10⁶ yeast cells/mL). C. albicans responded to incubation in hemolymph ex vivo by the induction of an oxidative stress response, a decrease in proteins associated with protein synthesis and an increase in glycolytic proteins. The results presented here indicate that C. albicans can overcome the fungicidal activity of hemolymph by altering protein synthesis and cellular respiration, and commence invasion and dissemination throughout the host.

Immune Response of Galleria mellonella against Human Fungal Pathogens

In many aspects, the immune response against pathogens in insects is similar to the innate immunity in mammals. This has caused a strong interest in the scientific community for the use of this model in research of host⁻pathogen interactions. In recent years, the use of Galleria mellonella larvae, an insect belonging to the Lepidoptera order, has emerged as an excellent model to study the virulence of human pathogens. It is a model that offers many advantages; for example, it is easy to handle and establish in every laboratory, the larvae have a low cost, and they tolerate a wide range of temperatures, including human temperature 37 °C. The immune response of G. mellonella is innate and is divided into a cellular component (hemocytes) and humoral component (antimicrobial peptides, lytic enzymes, and peptides and melanin) that work together against different intruders. It has been shown that the immune response of this insect has a great specificity and has the ability to distinguish between different classes of microorganisms. In this review, we delve into the different components of the innate immune response of Galleria mellonella, and how these components manifest in the infection of fungal pathogens including Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, and Histoplasma capsulatum.

Fusarium, an Entomopathogen-A Myth or Reality?

The Fusarium species has diverse ecological functions ranging from saprophytes, endophytes, and animal and plant pathogens. Occasionally, they are isolated from dead and alive insects. However, research on fusaria-insect associations is very limited as fusaria are generalized as opportunistic insect-pathogens. Additionally, their phytopathogenicity raises concerns in their use as commercial biopesticides. Insect biocontrol potential of Fusarium is favored by their excellent soil survivability as saprophytes, and sometimes, insect-pathogenic strains do not exhibit phytopathogenicity. In addition, a small group of fusaria, those belonging to the Fusarium solani species complex, act as insect mutualists assisting in host growth and fecundity. In this review, we summarize mutualism and pathogenicity among fusaria and insects. Furthermore, we assert on Fusarium entomopathogenicity by analyzing previous studies clearly demonstrating their natural insect-pathogenicity in fields, and their presence in soils. We also review the presence and/or production of a well-known insecticidal metabolite beauvericin by different Fusarium species. Lastly, some proof-of-concept studies are also summarized, which demonstrate the histological as well as immunological changes that a larva undergoes during Fusarium oxysporum pathogenesis. These reports highlight the insecticidal properties of some Fusarium spp., and emphasize the need of robust techniques, which can distinguish phytopathogenic, mutualistic and entomopathogenic fusaria.

Recent Advances in the Use of Galleria mellonella Model to Study Immune Responses against Human Pathogens

The use of invertebrates for in vivo studies in microbiology is well established in the scientific community. Larvae of Galleria mellonella are a widely used model for studying pathogenesis, the efficacy of new antimicrobial compounds, and immune responses. The immune system of G. mellonella larvae is structurally and functionally similar to the innate immune response of mammals, which makes this model suitable for such studies. In this review, cellular responses (hemocytes activity: phagocytosis, nodulation, and encapsulation) and humoral responses (reactions or soluble molecules released in the hemolymph as antimicrobial peptides, melanization, clotting, free radical production, and primary immunization) are discussed, highlighting the use of G. mellonella as a model of immune response to different human pathogenic microorganisms.

Identification and evaluation of Galleria mellonella peptides with antileishmanial activity

Leishmaniasis is a neglected disease, World Health Organization (WHO) declared it as high priority worldwide. Colombia is one of the 98 countries in which the disease caused more than 17.000 cases per year. There is a need to explore novel therapies to reduce the side effects of the current treatments. For this reason, this study was aimed to evaluate Galleria mellonella hemolymph for potential peptides with anti-parasitic activity. Larvae were challenged with Leishmania (V) panamensis promastigotes and hemolymph was analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), reversed-phase chromatography (RP-HPLC), two-dimensional gel electrophoresis and liquid chromatography-mass spectroscopy (LC/MS). The immunological response of Galleria mellonella was followed by SDS-PAGE, immunized hemolymph was fractionated by RP-HPLC where fractions 5 and 11 showed the highest antileishmanial activity. From these fractions 15 spots were isolated by 2D gel electrophoresis and evaluated by LC/MS to identify the peptides present in the spots. After the analysis Moricin-B, Moricin-C4, Cecropin-D and Anionic Peptide 2 were identified due to the immune challenge with Leishmania promastigotes. Anionic peptide 2 and Cecropin-D were synthesized and evaluated for antileishmanial activity. The results showed that Anionic peptide 2 presented more anti-parasitic activity. This study showed for the first time the anti-parasitic potential of peptides derived from hemolymph of Galleria mellonella.

Analysis of the early cellular and humoral responses of Galleria mellonella larvae to infection by Candida albicans

Galleria mellonella larvae were administered an inoculum of Candida albicans and the response to infection over 24 hours was monitored. The yeast cell density in infected larvae declined initially but replication commenced six hours post-infection. The hemocyte density decreased from 5.2 × 10⁶/ml to 2.5 × 10⁶/ml at 2 hours but increased to 4.2 × 106 at 6 hours and decreased subsequently. Administration of β – glucan to larvae also caused a fluctuation in hemocyte density (5.1 ± 0.22 × 10⁶/ml (0 hour) to 6.25 ± 0.25 × 106/ml (6 hour) (p < 0.05) to 5 ± 2.7 × 106 (24 hour)) and the population showed an increase in the density of small, granular cells at 24 hours (p < 0.05). Hemocytes from larvae inoculated with β – glucan for 6 or 24 hours showed faster killing of C. albicans cells (53 ± 4.1% (p < 0.01), 64 ± 3.7%, (p < 0.01), respectively) than hemocytes from control larvae (24 ± 11%) at 60 min. Proteomic analysis indicated increased abundance of immune related proteins cecropin-A (5 fold) and prophenoloxidase-activating proteinase-1 (5 fold) 6 hours post infection but by 24 hours there was elevated abundance of muscle (tropomyosin 2 (141 fold), calponin (66 fold), troponin I (62 fold)) and proteins indicative of cellular stress (glutathione-S-transferase-like protein (114 fold)), fungal dissemination (muscle protein 20-like protein (174 fold)) and tissue breakdown (mitochondrial cytochrome c (10 fold)). Proteins decreased in abundance at 24 hour included β – 1,3 – glucan recognition protein precursor (29 fold) and prophenoloxidase subunit 2 (25 fold).

Humoral immune response of Galleria mellonella after repeated infection with Bacillus thuringiensis

The insect immune system relies on innate mechanisms only. However, there is an increasing number of data reporting that previous immune challenge with microbial elicitors or a low number of microorganisms can modulate susceptibility after subsequent lethal infection with the same or different pathogen. This phenomenon is called immune priming. Its biochemical and molecular mechanisms remain unravelled. Here we present that Galleria mellonella larvae that survived infection induced by intrahemocelic injection of a low dose of Bacillus thuringiensis were more resistant to re-injection of a lethal dose of the same bacteria but not other bacteria and fungi tested. This correlated with enhanced activity detected in full hemolymph as well as in separated hemolymph polypeptides. In addition, we observed differences in the hemolymph protein pattern between primed and non-primed larvae after infection with the lethal dose of B. thuringiensis. Expression of genes encoding inducible defence molecules was not enhanced in the primed larvae after the infection with the lethal dose of B. thuringiensis. It is likely that priming affects the turnover of immune related hemolymph proteins; hence, upon repeated contact, the immune response may be more ergonomic.

Immunity of the greater wax moth Galleria mellonella

Investigation of insect immune mechanisms provides important information concerning innate immunity, which in many aspects is conserved in animals. This is one of the reasons why insects serve as model organisms to study virulence mechanisms of human pathogens. From the evolutionary point of view, we also learn a lot about host-pathogen interaction and adaptation of organisms to conditions of life. Additionally, insect-derived antibacterial and antifungal peptides and proteins are considered for their potential to be applied as alternatives to antibiotics. While Drosophila melanogaster is used to study the genetic aspect of insect immunity, Galleria mellonella serves as a good model for biochemical research. Given the size of the insect, it is possible to obtain easily hemolymph and other tissues as a source of many immune-relevant polypeptides. This review article summarizes our knowledge concerning G. mellonella immunity. The best-characterized immune-related proteins and peptides are recalled and their short characteristic is given. Some other proteins identified at the mRNA level are also mentioned. The infectious routes used by Galleria natural pathogens such as Bacillus thuringiensis and Beauveria bassiana are also described in the context of host-pathogen interaction. Finally, the plasticity of G. mellonella immune response influenced by abiotic and biotic factors is described.

Characterization and regulation of expression of an antifungal peptide from hemolymph of an insect, Manduca sexta

Insects secrete antimicrobial peptides as part of the innate immune response. Most antimicrobial peptides from insects have antibacterial but not antifungal activity. We have characterized an antifungal peptide, diapausin-1 from hemolymph of a lepidopteran insect, Manduca sexta (tobacco hornworm). Diapausin-1 was isolated by size exclusion chromatography from hemolymph plasma of larvae that were previously injected with a yeast, Saccharomyces cerevisiae. Fractions containing activity against S. cerevisiae were analyzed by SDS-PAGE and MALDI-TOF MS/MS and found to contain a 45-residue peptide that was encoded by sequences identified in M. sexta transcriptome and genome databases. A cDNA for diapausin-1 was cloned from cDNA prepared from fat body RNA. Diapausin-1 is a member of the diapausin family of peptides, which includes members known to have antifungal activity. The M. sexta genome contains 14 genes with high similarity to diapausin-1, each with 6 conserved Cys residues. Diapausin-1 was produced as a recombinant protein in Escherichia coli. Purified recombinant diapausin-1 was active against S. cerevisiae, with IC50 of 12 μM, but had no detectable activity against bacteria. Spores of some plant fungal pathogens treated with diapausin-1 had curled germination tubes or reduced and branched hyphal growth. Diapausin-1 mRNA level in fat body strongly increased after larvae were injected with yeast or with Micrococcus luteus. In addition, diapausin-1 mRNA levels increased in midgut and fat body at the wandering larval stage prior to pupation, suggesting developmental regulation of the gene. Our results indicate that synthesis of diapausin-1 is part of an antifungal innate immune response to infection in M. sexta.

Entomopathogenic Fungi: New Insights into Host-Pathogen Interactions

Although many insects successfully live in dangerous environments exposed to diverse communities of microbes, they are often exploited and killed by specialist pathogens. Studies of host-pathogen interactions (HPI) provide valuable insights into the dynamics of the highly aggressive coevolutionary arms race between entomopathogenic fungi (EPF) and their arthropod hosts. The host defenses are designed to exclude the pathogen or mitigate the damage inflicted while the pathogen responds with immune evasion and utilization of host resources. EPF neutralize their immediate surroundings on the insect integument and benefit from the physiochemical properties of the cuticle and its compounds that exclude competing microbes. EPF also exhibit adaptations aimed at minimizing trauma that can be deleterious to both host and pathogen (eg, melanization of hemolymph), form narrow penetration pegs that alleviate host dehydration and produce blastospores that lack immunogenic sugars/enzymes but facilitate rapid assimilation of hemolymph nutrients. In response, insects deploy an extensive armory of hemocytes and macromolecules, such as lectins and phenoloxidase, that repel, immobilize, and kill EPF. New evidence suggests that immune bioactives work synergistically (eg, lysozyme with antimicrobial peptides) to combat infections. Some proteins, including transferrin and apolipophorin III, also demonstrate multifunctional properties, participating in metabolism, homeostasis, and pathogen recognition. This review discusses the molecular intricacies of these HPI, highlighting the interplay between immunity, stress management, and metabolism. Increased knowledge in this area could enhance the efficacy of EPF, ensuring their future in integrated pest management programs.

Galleria mellonella infection models for the study of bacterial diseases and for antimicrobial drug testing

Galleria mellonella (greater wax moth or honeycomb moth) has been introduced as an alternative model to study microbial infections. G. mellonella larvae can be easily and inexpensively obtained in large numbers and are simple to use as they don't require special lab equipment. There are no ethical constraints and their short life cycle makes them ideal for large-scale studies. Although insects lack an adaptive immune response, their innate immune response shows remarkable similarities with the immune response in vertebrates. This review gives a current update of what is known about the immune system of G. mellonella and provides an extensive overview of how G. mellonella is used to study the virulence of Gram-positive and Gram-negative bacteria. In addition, the use of G. mellonella to evaluate the efficacy of antimicrobial agents and experimental phage therapy are also discussed. The review concludes with a critical assessment of the current limitatons of G. mellonella infection models.

Insect antimicrobial peptides and their applications

Insects are one of the major sources of antimicrobial peptides/proteins (AMPs). Since observation of antimicrobial activity in the hemolymph of pupae from the giant silk moths Samia Cynthia and Hyalophora cecropia in 1974 and purification of first insect AMP (cecropin) from H. cecropia pupae in 1980, over 150 insect AMPs have been purified or identified. Most insect AMPs are small and cationic, and they show activities against bacteria and/or fungi, as well as some parasites and viruses. Insect AMPs can be classified into four families based on their structures or unique sequences: the α-helical peptides (cecropin and moricin), cysteine-rich peptides (insect defensin and drosomycin), proline-rich peptides (apidaecin, drosocin, and lebocin), and glycine-rich peptides/proteins (attacin and gloverin). Among insect AMPs, defensins, cecropins, proline-rich peptides, and attacins are common, while gloverins and moricins have been identified only in Lepidoptera. Most active AMPs are small peptides of 20-50 residues, which are generated from larger inactive precursor proteins or pro-proteins, but gloverins (~14 kDa) and attacins (~20 kDa) are large antimicrobial proteins. In this mini-review, we will discuss current knowledge and recent progress in several classes of insect AMPs, including insect defensins, cecropins, attacins, lebocins and other proline-rich peptides, gloverins, and moricins, with a focus on structural-functional relationships and their potential applications.

Studies on the role of insect hemolymph polypeptides: Galleria mellonella anionic peptide 2 and lysozyme

The lysozymes are well known antimicrobial polypeptides exhibiting antibacterial and antifungal activities. Their antibacterial potential is related to muramidase activity and non-enzymatic activity resembling the mode of action of cationic defense peptides. However, the mechanisms responsible for fungistatic and/or fungicidal activity of lysozyme are still not clear. In the present study, the anti-Candida albicans activity of Galleria mellonella lysozyme and anionic peptide 2 (AP2), defense factors constitutively present in the hemolymph, was examined. The lysozyme inhibited C. albicans growth in a dose-dependent manner. The decrease in the C. albicans survival rate caused by the lysozyme was accompanied by a considerable reduction of the fungus metabolic activity, as revealed by LIVE/DEAD staining. In contrast, although AP2 reduced C. albicans metabolic activity, it did not influence its survival rate. Our results suggest fungicidal action of G. mellonella lysozyme and fungistatic activity of AP2 toward C. albicans cells. In the presence of AP2, the anti-C. albicans activity of G. mellonella lysozyme increased. Moreover, when the fungus was incubated with both defense factors, true hyphae were observed besides pseudohyphae and yeast-like C. albicans cells. Atomic force microscopy analysis of the cells exposed to the lysozyme and/or AP2 revealed alterations in the cell surface topography and properties in comparison with the control cells. The results indicate synergistic action of G. mellonella AP2 and lysozyme toward C. albicans. The presence of both factors in the hemolymph of naive larvae suggests their important role in the early stages of immune response against fungi in G. mellonella.

Properties and mechanisms of action of naturally occurring antifungal peptides

Antimicrobial peptides are a vital component of the innate immune system of all eukaryotic organisms and many of these peptides have potent antifungal activity. They have potential application in the control of fungal pathogens that are a serious threat to both human health and food security. Development of antifungal peptides as therapeutics requires an understanding of their mechanism of action on fungal cells. To date, most research on antimicrobial peptides has focused on their activity against bacteria. Several antimicrobial peptides specifically target fungal cells and are not active against bacteria. Others with broader specificity often have different mechanisms of action against bacteria and fungi. This review focuses on the mechanism of action of naturally occurring antifungal peptides from a diverse range of sources including plants, mammals, amphibians, insects, crabs, spiders, and fungi. While antimicrobial peptides were originally proposed to act via membrane permeabilization, the mechanism of antifungal activity for these peptides is generally more complex and often involves entry of the peptide into the cell.

Galleria mellonella infected with Bacillus thuringiensis involves Hsp90

Insects are good models for studying the innate immune response. We report that Galleria mellonella larvae infected with entomopathogenic bacteria Bacillus thuringiensis kurstaki show changes in the level of Hsp90. Our experimental approach was to pre-treat larvae with the Hsp90-binding compound, 17-DMAG, before infection with B. thuringiensis. We show that pre-treated animals display a higher level of immune response. This was mainly manifested by enhanced action of their hemolymph directed toward living bacteria as well as lysozyme activity digesting bacterial peptidoglycan. The observed phenomenon was due to the higher activity of antimicrobial peptides which, in contrast to healthy animals, was detected in the hemolymph of the immunestimulated larvae. Finally, the physiological significance of our observation was highlighted by the fact that G. mellonella pre-treated with 17-DMAG showed a prolonged survival rate after infection with B. thuringiensis than the control animals. Our report points to a role for Hsp90 in the immune response of G. mellonella after infection with B. thuringiensis at the optimal growth temperature.

Anti-Legionella dumoffii activity of Galleria mellonella defensin and apolipophorin III

The gram-negative bacterium Legionella dumoffii is, beside Legionella pneumophila, an etiological agent of Legionnaires’ disease, an atypical form of pneumonia. The aim of this study was to determine the antimicrobial activity of Galleria mellonella defense polypeptides against L. dumoffii. The extract of immune hemolymph, containing a mixture of defense peptides and proteins, exhibited a dose-dependent bactericidal effect on L. dumoffii. The bacterium appeared sensitive to a main component of the hemolymph extract, apolipophorin III, as well as to a defense peptide, Galleria defensin, used at the concentrations 0.4 mg/mL and 40 μg/mL, respectively. L. dumoffii cells cultured in the presence of choline were more susceptible to both defense factors analyzed. A transmission electron microscopy study of bacterial cells demonstrated that Galleria defensin and apolipophorin III induced irreversible cell wall damage and strong intracellular alterations, i.e., increased vacuolization, cytoplasm condensation and the appearance of electron-white spaces in electron micrographs. Our findings suggest that insects, such as G. mellonella, with their great diversity of antimicrobial factors, can serve as a rich source of compounds for the testing of Legionella susceptibility to defense-related peptides and proteins.

Manduca sexta moricin promoter elements can increase promoter activities of Drosophila melanogaster antimicrobial peptide genes

Insects produce a variety of antimicrobial peptides (AMPs). Induction of insect AMP genes is regulated by the Toll and IMD (immune deficiency) pathways via NF-κB and GATA factors. Little is known about species-specific regulation of AMP genes. In this report, we showed that activities of most Manduca sexta and Drosophila melanogaster AMP gene promoters were regulated in a species-specific manner in Drosophila (Dipteran) S2 cells and Spodoptera frugiperda (Lepidopteran) Sf9 cells. A κB-GATA element (22 bp) from M. sexta moricin (MsMoricin) promoter could significantly increase activities of Drosophila AMP gene promoters in S2 cells, and an MsMoricin promoter activating element (MPAE) (140 bp) could increase activity of drosomycin promoter specifically in Sf9 cells. However, κB and GATA factors alone were not sufficient for MsMoricin gene activation, suggesting that other co-regulators may be required to fully activate AMP genes. Our results suggest that induction of insect AMP genes may require a transcription complex composed of common nuclear factors (such as NF-κB and GATA factors) and species-related co-regulators, and it is the co-regulators that may confer species-specific regulation of AMP genes. In addition, we showed that activity of Drosophila drosomycin promoter could be activated cooperatively by the inserted exogenous κB-GATA element and the endogenous κB element. These findings revealed an approach of engineering AMP genes with enhanced activities, which may lead to broad applications.

Fusarium pathogenesis investigated using Galleria mellonella as a heterologous host

Members of the fungal genus Fusarium are capable of manifesting in a multitude of clinical infections, most commonly in immunocompromised patients. In order to better understand the interaction between the fungus and host, we have developed the larvae of the greater wax moth, Galleria mellonella, as a heterologous host for fusaria. When conidia are injected into the haemocoel of this Lepidopteran system, both clinical and environmental isolates of the fungus are able to kill the larvae at 37 °C, although killing occurs more rapidly when incubated at 30 °C. This killing was dependent on several other factors besides temperature, including the Fusarium strain, the number of conidia injected, and the conidia morphology, where macroconidia are more virulent than their microconidia counterpart. There was a correlation in the killing rate of Fusarium spp. when evaluated in G. mellonella and a murine model. In vivo studies indicated G. mellonella haemocytes were capable of initially phagocytosing both conidial morphologies. The G. mellonella system was also used to evaluate antifungal agents, and amphotericin B was able to confer a significant increase in survival to Fusarium-infected larvae. The G. mellonella-Fusarium pathogenicity system revealed that virulence of Fusarium spp. is similar, regardless of the origin of the isolate, and that mammalian endothermy is a major deterrent for Fusarium infection and therefore provides a suitable alternative to mammalian models to investigate the interaction between the host and this increasingly important fungal pathogen.

A comprehensive transcriptome and immune-gene repertoire of the lepidopteran model host Galleria mellonella

Background

The larvae of the greater wax moth Galleria mellonella are increasingly used (i) as mini-hosts to study pathogenesis and virulence factors of prominent bacterial and fungal human pathogens, (ii) as a whole-animal high throughput infection system for testing pathogen mutant libraries, and (iii) as a reliable host model to evaluate the efficacy of antibiotics against human pathogens. In order to compensate for the lack of genomic information in Galleria, we subjected the transcriptome of different developmental stages and immune-challenged larvae to next generation sequencing.

Results

We performed a Galleria transcriptome characterization on the Roche 454-FLX platform combined with traditional Sanger sequencing to obtain a comprehensive transcriptome. To maximize sequence diversity, we pooled RNA extracted from different developmental stages, larval tissues including hemocytes, and from immune-challenged larvae and normalized the cDNA pool. We generated a total of 789,105 pyrosequencing and 12,032 high-quality Sanger EST sequences which clustered into 18,690 contigs with an average length of 1,132 bases. Approximately 40% of the ESTs were significantly similar (E ≤ e^-03) to proteins of other insects, of which 45% have a reported function. We identified a large number of genes encoding proteins with established functions in immunity related sensing of microbial signatures and signaling, as well as effector molecules such as antimicrobial peptides and inhibitors of microbial proteinases. In addition, we found genes known as mediators of melanization or contributing to stress responses. Using the transcriptomic data, we identified hemolymph peptides and proteins induced upon immune challenge by 2D-gelelectrophoresis combined with mass spectrometric analysis.

Conclusion

Here, we have developed extensive transcriptomic resources for Galleria. The data obtained is rich in gene transcripts related to immunity, expanding remarkably our knowledge about immune and stress-inducible genes in Galleria and providing the complete sequences of genes whose primary structure have only partially been characterized using proteomic methods. The generated data provide for the first time access to the genetic architecture of immunity in this model host, allowing us to elucidate the molecular mechanisms underlying pathogen and parasite response and detailed analyses of both its immune responses against human pathogens, and its coevolution with entomopathogens.

Immunity in lepidopteran insects

Lepidopteran insects provide important model systems for innate immunity of insects, particularly for cell biology of hemocytes and biochemical analyses of plasma proteins. Caterpillars are also among the most serious agricultural pests, and understanding of their immune systems has potential practical significance. An early response to infection in lepidopteran larvae is the activation of hemocyte adhesion, leading to phagocytosis, nodule formation, or encapsulation. Plasmatocytes and granular cells are the hemocyte types involved in these responses. Infectious microorganisms are recognized by binding of hemolymph plasma proteins to microbial surface components. This "pattern recognition" triggers phagocytosis and nodule formation, activation of prophenoloxidase and melanization and the synthesis of antimicrobial proteins that are secreted into the hemolymph. Many hemolymph proteins that function in such innate immune responses of insects were first discovered in lepidopterans. Microbial proteinases and nucleic acids released from lysed host cells may also activate lepidopteran immune responses. Hemolymph antimicrobial peptides and proteins can reach high concentrations and may have activity against a broad spectrum of microorganisms, contributing significantly to clearing of infections. Serine proteinase cascade pathways triggered by microbial components interacting with pattern recognition proteins stimulate activation of the cytokine Spätzle, which initiates the Toll pathway for expression of antimicrobial peptides. A proteinase cascade also results inproteolytic activation of phenoloxidase and production of melanin coatings that trap and kill parasites and pathogens. The proteinases in hemolymph are regulated by specific inhibitors, including members of the serpin superfamily. New developments in lepidopteran functional genomics should lead to much more complete understanding of the immune systems of this insect group.

Galleria mellonella are resistant to Pneumocystis murina infection

Studying Pneumocystis has proven to be a challenge from the perspective of propagating a significant amount of the pathogen in a facile manner. The study of several fungal pathogens has been aided by the use of invertebrate model hosts. Our efforts to infect the invertebrate larvae Galleria mellonella with Pneumocystis proved futile since P. murina neither caused disease nor was able to proliferate within G. mellonella. It did, however, show that the pathogen could be rapidly cleared from the host.

A different repertoire of Galleria mellonella antimicrobial peptides in larvae challenged with bacteria and fungi

To date, functioning of insect humoral immune response is especially well described in Diptera. The mechanisms of pathogen recognition, activation of signaling pathways and regulation of antimicrobial defense peptide expression are relatively well known. The present paper demonstrates evidence that the immune system of the Lepidoptera moth, Galleria mellonella, is also able to distinguish between different classes of microorganisms and responds to the invading pathogen accordingly. G. mellonella larvae were challenged with Gram-negative and Gram-positive bacteria as well as with yeast and filamentous fungus cells. Subsequently, 24, 48 and 72 h after immunization, the concentrations of lysozyme and six defense peptides were determined in the hemolymph by the HPLC technique. The compounds studied demonstrated variability both in the kinetics of the increase as well as in the concentrations reached. The Gram-negative bacterium and filamentous fungus were particularly effective immunogens, especially affecting the levels of lysozyme, Galleria defensin, proline-rich peptide 2 and cecropin D-like peptide.

A peptidomics study reveals the impressive antimicrobial peptide arsenal of the wax moth Galleria mellonella

The complete antimicrobial peptide repertoire of Galleria mellonella was investigated for the first time by LC/MS. Combining data from separate trypsin, Glu-C and Asp-N digests of immune hemolymph allowed detection of 18 known or putative G. mellonella antimicrobial peptides or proteins, namely lysozyme, moricin-like peptides (5), cecropins (2), gloverin, Gm proline-rich peptide 1, Gm proline-rich peptide 2, Gm anionic peptide 1 (P1-like), Gm anionic peptide 2, galiomicin, gallerimycin, inducible serine protease inhibitor 2, 6tox and heliocin-like peptide. Six of these were previously known only as nucleotide sequences, so this study provides the first evidence for expression of these genes. LC/MS data also provided insight into the expression and processing of the antimicrobial Gm proline-rich peptide 1. The gene for this peptide was isolated and shown to be unique to moths and to have an unusually long precursor region (495 bp). The precursor region contained other proline-rich peptides and LC/MS data suggested that these were being specifically processed and were present in hemolymph at very high levels. This study shows that G. mellonella can concurrently release an impressive array of at least 18 known or putative antimicrobial peptides from 10 families to defend itself against invading microbes.

The dlt operon of Bacillus cereus is required for resistance to cationic antimicrobial peptides and for virulence in insects

The dlt operon encodes proteins that alanylate teichoic acids, the major components of cell walls of gram-positive bacteria. This generates a net positive charge on bacterial cell walls, repulsing positively charged molecules and conferring resistance to animal and human cationic antimicrobial peptides (AMPs) in gram-positive pathogenic bacteria. AMPs damage the bacterial membrane and are the most effective components of the humoral immune response against bacteria. We investigated the role of the dlt operon in insect virulence by inactivating this operon in Bacillus cereus, which is both an opportunistic human pathogen and an insect pathogen. The Delta dlt(Bc) mutant displayed several morphological alterations but grew at a rate similar to that for the wild-type strain. This mutant was less resistant to protamine and several bacterial cationic AMPs, such as nisin, polymyxin B, and colistin, in vitro. It was also less resistant to molecules from the insect humoral immune system, lysozyme, and cationic AMP cecropin B from Spodoptera frugiperda. Delta dlt(Bc) was as pathogenic as the wild-type strain in oral infections of Galleria mellonella but much less virulent when injected into the hemocoels of G. mellonella and Spodoptera littoralis. We detected the dlt operon in three gram-negative genera: Erwinia (Erwinia carotovora), Bordetella (Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica), and Photorhabdus (the entomopathogenic bacterium Photorhabdus luminescens TT01, the dlt operon of which did not restore cationic AMP resistance in Delta dlt(Bc)). We suggest that the dlt operon protects B. cereus against insect humoral immune mediators, including hemolymph cationic AMPs, and may be critical for the establishment of lethal septicemia in insects and in nosocomial infections in humans.