Identification of immunorelevant genes from greater wax moth (Galleria mellonella) by a subtractive hybridization approach

Immune priming modulates Galleria mellonella and Pseudomonas entomophila interaction. Antimicrobial properties of Kazal peptide Pr13a

Galleria mellonella larvae repeatedly infected with Pseudomonas entomophila bacteria re-induced their immune response. Its parameters, i.e. the defence activities of cell-free hemolymph, the presence and activity of antimicrobial peptides, and the expression of immune-relevant genes were modulated after the re-challenge in comparison to non-primed infected larvae, resulting in better protection. No enhanced resistance was observed when the larvae were initially infected with other microorganisms, and larvae pre-infected with P. entomophila were not more resistant to further infection with other pathogens. Then, the peptide profiles of hemolymph from primed- and non-primed larvae infected with P. entomophila were compared by quantitative RP-HPLC (Reverse Phase - High Performance Liquid Chromatography). The level of carbonic anhydrase, anionic peptide-1, proline peptide-2, and finally, unknown so far, putative Kazal peptide Pr13a was higher in the primed infected animals than in the larvae infected with P. entomophila for the first time. The expression of the Pr13a gene increased two-fold after the infection, but only in the primed animals. To check whether the enhanced level of Pr13a could have physiological significance, the peptide was purified to homogeneity and checked for its defence properties. In fact, it had antibacterial activity: at the concentration of 15 µM and 7.5 µM it reduced the number of P. entomophila and Bacillus thuringiensis CFU, respectively, to about 40%. The antibacterial activity of Pr13a was correlated with changes observed on the surface of the peptide-treated bacteria, e.g. surface roughness and adhesion force. The presented results bring us closer to finding hemolymph constituents responsible for the effect of priming on the immune response in re-infected insects.

Defence response of Galleria mellonella larvae to oral and intrahemocelic infection with Pseudomonasentomophila

We report differences in the course of infection of G. mellonella larvae with P. entomophila via intrahemocelic and oral routes. Survival curves, larval morphology, histology, and induction of defence response were investigated. Larvae injected with 10 and 50 cells of P. entomophila activated a dose-dependent immune response, which was manifested by induction of immune-related genes and dose-dependent defence activity in larval hemolymph. In contrast, after the oral application of the pathogen, antimicrobial activity was detected in whole hemolymph of larvae infected with the 103 but not 105 dose in spite of the induction of immune response manifested as immune-relevant gene expression and defence activity of electrophoretically separated low-molecular hemolymph components. Among known proteins induced after the P. entomophila infection, we identified proline-rich peptide 1 and 2, cecropin D-like peptide, galiomycin, lysozyme, anionic peptide 1, defensin-like peptide, and a 27 kDa hemolymph protein. The expression of the lysozyme gene and the amount of protein in the hemolymph were correlated with inactivity of hemolymph in insects orally infected with a higher dose of P. entomophila, pointing to its role in the host-pathogen interaction.

Insect fungal pathogens secrete a cell wall-associated glucanase that acts to help avoid recognition by the host immune system

Fungal insect pathogens have evolved diverse mechanisms to evade host immune recognition and defense responses. However, identification of fungal factors involved in host immune evasion during cuticular penetration and subsequent hemocoel colonization remains limited. Here, we report that the entomopathogenic fungus Beauveria bassiana expresses an endo-β-1,3-glucanase (BbEng1) that functions in helping cells evade insect immune recognition/ responses. BbEng1 was specifically expressed during infection, in response to host cuticle and hemolymph, and in the presence of osmotic or oxidative stress. BbEng1 was localized to the fungal cell surface/ cell wall, where it acts to remodel the cell wall pathogen associated molecular patterns (PAMPs) that can trigger host defenses, thus facilitating fungal cell evasion of host immune defenses. BbEng1 was secreted where it could bind to fungal cells. Cell wall β-1,3-glucan levels were unchanged in ΔBbEng1 cells derived from in vitro growth media, but was elevated in hyphal bodies, whereas glucan levels were reduced in most cell types derived from the BbEng1 overexpressing strain (BbEng1OE). The BbEng1OE strain proliferated more rapidly in the host hemocoel and displayed higher virulence as compared to the wild type parent. Overexpression of their respective Eng1 homologs or of BbEng1 in the insect fungal pathogens, Metarhizium robertsii and M. acridum also resulted in increased virulence. Our data support a mechanism by which BbEng1 helps the fungal pathogen to evade host immune surveillance by decreasing cell wall glucan PAMPs, promoting successful fungal mycosis.

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.

Galleria mellonella: The Versatile Host for Drug Discovery, In Vivo Toxicity Testing and Characterising Host-Pathogen Interactions

Larvae of the greater wax moth, Galleria mellonella, are a convenient in vivo model for assessing the activity and toxicity of antimicrobial agents and for studying the immune response to pathogens and provide results similar to those from mammals. G. mellonella larvae are now widely used in academia and industry and their use can assist in the identification and evaluation of novel antimicrobial agents. Galleria larvae are inexpensive to purchase and house, easy to inoculate, generate results within 24–48 h and their use is not restricted by legal or ethical considerations. This review will highlight how Galleria larvae can be used to assess the efficacy of novel antimicrobial therapies (photodynamic therapy, phage therapy, metal-based drugs, triazole-amino acid hybrids) and for determining the in vivo toxicity of compounds (e.g., food preservatives, ionic liquids) and/or solvents (polysorbate 80). In addition, the disease development processes are associated with a variety of pathogens (e.g., Staphylococcus aureus, Listeria monocytogenes, Aspergillus fumigatus, Madurella mycotomatis) in mammals are also present in Galleria larvae thus providing a simple in vivo model for characterising disease progression. The use of Galleria larvae offers many advantages and can lead to an acceleration in the development of novel antimicrobials and may be a prerequisite to mammalian testing.

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.

Manipulation of host ecdysteroid hormone levels facilitates infection by the fungal insect pathogen, Metarhizium rileyi

Entomopathogenic fungi such as Metarhizium rileyi and Beauveria bassiana are widely used insect biological control agents. Little, however, is known concerning genetic or enzymatic factors that differentiate the mechanisms employed by these two fungal pathogens to infect target hosts. Infection by either of these organisms is known to increase levels of the growth and molting hormone, ecdysone, which also regulates the expression of a number of innate immune pathways. M. rileyi, but not B. bassiana, has apparently evolved an ecdysteroid-22-oxidase (MrE22O) that inactivate ecdysone. We show that deletion of MrE22O impaired virulence compared with the wild-type strain, with an increase in ecdysone titer seen in hosts that was coupled to an increase in the expression of antimicrobial genes. An M. rileyi strain engineered to overexpress MrE22O (MrE22O^OE ), as well as trans-expression in B. bassiana (Bb::MrE220^OE ) resulted, in strains displaying enhanced virulence and dampening of host immune responses compared with their respective wild-type parental strains. These results indicate that ecdysone plays an important role in mediating responses to fungal infection and that some insect pathogenic fungi have evolved mechanisms for targeting this hormone as a means for facilitating infection.

The innate immune gene Relish and Caudal jointly contribute to the gut immune homeostasis by regulating antimicrobial peptides in Galleria mellonella

Gut microbiota modulates various physiologic processes in insects, such as nutrition, metabolic homeostasis, and pathogen exclusion. Maintaining a normal microbiome is an essential element of the gut homeostasis, requiring an extensive network of regulatory immune responses. The molecular mechanisms driving these various effects and the events leading to the establishment of a normal microbiota in insects are still largely unknown. In this study, the NF-kB (IMD and Toll) signaling pathways in the gut of Galleria mellonella and their roles in the regulation of its gut microbes were assessed. For this, the transcript levels of the IMD pathway (Imd and Relish) and the Toll pathway (Spätzle and Dif/Dorsal) genes were analyzed and the results showed that all the genes were expressed in the gut of G. mellonella. Silencing of Relish resulted in reduced expression levels of the IMD pathway genes and antimicrobial peptides (AMPs) followed by overpopulation of gut bacteria. Antibiotics-treated larvae showed lower expression levels of the IMD and Toll pathway genes followed by lower AMPs expression levels. The expression level of caudal decreased in the antibiotics-treated larvae compared with the controls. Together, these data suggest that the IMD and Toll pathways are active in the gut of G. mellonella. The IMD pathway gene, relish functions in the regulation of gut microbes in this insect model.

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.

Immune transcriptome analysis in predatory beetles reveals two cecropin genes overexpressed in mandibles

The great complexity and variety of the innate immune system and the production of antimicrobial peptides in insects is correlated with their evolutionary success and adaptation to different environments. Tiger beetles are an example of non-pest species with a cosmopolitan distribution, but the immune system is barely known and its study could provide useful information about the humoral immunity of predatory insects. Suppression subtractive hybridization (SSH) was performed in Calomera littoralis beetles to obtain a screening of those genes that were overexpressed after an injection with Escherichia coli lipopolysaccharide (LPS). Several genes were identified to be related to immune defense. Among those genes, two members of the cecropin antimicrobial peptides were characterized and identified as CliCec-A and CliCec-B2. Both protein sequences showed cecropin characteristics including 37 and 38 residue mature peptides, composed by two α-helices structures with amphipathic and hydrophobic nature, as shown in their predicted three-dimensional structure. Chemically synthesized CliCec-B2 confirmed cecropin antimicrobial activity against some Gram (+) and Gram (-) bacteria, but not against yeast. Expression of both cecropin genes was assessed by qPCR and showed increases after a LPS injection and highlighted their overexpression in adult beetle mandibles, which could be related to their alimentary habits.

New Perspectives on Galleria mellonella Larvae as a Host Model Using Riemerella anatipestifer as a Proof of Concept

Galleria mellonella larvae have been used as a host model to study interactions between pathogens and hosts for several years. However, whether the model is useful to interrogate Riemerella anatipestifer infection biology remained unknown. This study aimed to exploit the potential of G. mellonella larvae and reveal their limitations as a host model for R. anatipestifer infection. G. mellonella larvae were shown to be effective for virulence evaluations of different R. anatipestifer strains. Furthermore, the virulent strain R. anatipestifer CH-1 had a stronger ability to proliferate than the attenuated strain R. anatipestifer ATCC 11845 in both G. mellonella larvae and ducklings. Unconventionally it was shown that G. mellonella larvae cannot be used to evaluate the efficacy of antimicrobials and their combinations. Additionally, it was shown that certain virulence factors, such as OmpA (B739_0861), B739_1208, B739_1343, and Wza (B739_1124), were specific only for ducklings, suggesting that G. mellonella larvae must be cautiously used to identify virulence factors of R. anatipestifer Evaluation of heme uptake-related virulence genes, such as tonB1 and tonB2, required preincubating the strains with hemoglobin before infection of G. mellonella larvae since R. anatipestifer cannot obtain a heme source from G. mellonella larvae. In conclusion, this study revealed the applicability and limitations of G. mellonella as a model with which to study the pathogen-host interaction, particularly in the context of R. anatipestifer infection.

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.

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.

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.

Stress Response Protein BolA Influences Fitness and Promotes Salmonella enterica Serovar Typhimurium Virulence

The intracellular pathogen Salmonella enterica serovar Typhimurium has emerged as a major cause of foodborne illness, representing a severe clinical and economic concern worldwide. The capacity of this pathogen to efficiently infect and survive inside the host depends on its ability to synchronize a complex network of virulence mechanisms. Therefore, the identification of new virulence determinants has become of paramount importance in the search of new targets for drug development. BolA-like proteins are widely conserved in all kingdoms of life. In Escherichia coli, this transcription factor has a critical regulatory role in several mechanisms that are tightly related to bacterial virulence. Therefore, in the present work we used the well-established infection model Galleria mellonella to evaluate the role of BolA protein in S Typhimurium virulence. We have shown that BolA is an important player in S Typhimurium pathogenesis. Specifically, the absence of BolA leads to a defective virulence capacity that is most likely related to the remarkable effect of this protein on S Typhimurium evasion of the cellular response. Furthermore, it was demonstrated that BolA has a critical role in bacterial survival under harsh conditions since BolA conferred protection against acidic and oxidative stress. Hence, we provide evidence that BolA is a determining factor in the ability of Salmonella to survive and overcome host defense mechanisms, and this is an important step in progress to an understanding of the pathways underlying bacterial virulence.IMPORTANCE BolA has been described as an important protein for survival in the late stages of bacterial growth and under harsh environmental conditions. High levels of BolA in stationary phase and under stresses have been connected with a plethora of phenotypes, strongly suggesting its important role as a master regulator. Here, we show that BolA is a determining factor in the ability of Salmonella to survive and overcome host defense mechanisms, and this is an important step in progress to an understanding of the pathways underlying bacterial virulence. This work constitutes a relevant step toward an understanding of the role of BolA protein and may have an important impact on future studies in other organisms. Therefore, this study is of utmost importance for understanding the genetic and molecular bases involved in the regulation of Salmonella virulence and may contribute to future industrial and public health care applications.

Transcriptome analysis of sugar beet root maggot (Tetanops myopaeformis) genes modulated by the Beta vulgaris host

Sugar beet root maggot (SBRM, Tetanops myopaeformis von Röder) is a major but poorly understood insect pest of sugar beet (Beta vulgaris L.). The molecular mechanisms underlying plant defense responses are well documented, however, little information is available about complementary mechanisms for insect adaptive responses to overcome host resistance. To date, no studies have been published on SBRM gene expression profiling. Suppressive subtractive hybridization (SSH) generated more than 300 SBRM ESTs differentially expressed in the interaction of the pest with a moderately resistant (F1016) and a susceptible (F1010) sugar beet line. Blast2GO v. 3.2 search indicated that over 40% of the differentially expressed genes had known functions, primarily driven by fruit fly D. melanogaster genes. Expression patterns of 18 selected EST clones were confirmed by RT-PCR analysis. Gene Ontology (GO) analysis predicted a dominance of metabolic and catalytic genes involved in the interaction of SBRM with its host. SBRM genes functioning during development, regulation, cellular process, signaling and under stress conditions were annotated. SBRM genes that were common or unique in response to resistant or susceptible interactions with the host were identified and their possible roles in insect responses to the host are discussed.

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.

Optimized expression of the antimicrobial protein Gloverin from Galleria mellonella using stably transformed Drosophila melanogaster S2 cells

Antimicrobial proteins and peptides (AMPs) are valuable as leads in the pharmaceutical industry for the development of novel anti-infective drugs. Here we describe the efficient heterologous expression and basic characterization of a Gloverin-family AMP derived from the greater wax moth Galleria mellonella. Highly productive single-cell clones prepared by limiting dilution achieved a 100% increase in productivity compared to the original polyclonal Drosophila melanogaster S2 cell line. Comprehensive screening for suitable expression conditions using statistical experimental designs revealed that optimal induction was achieved using 600 µM CuSO4 at the mid-exponential growth phase. Under these conditions, 25 mg/L of the AMP was expressed at the 1-L bioreactor scale, with optimal induction and harvest times ensured by dielectric spectroscopy and the online measurement of optical density. Gloverin was purified from the supernatant by immobilized metal ion affinity chromatography followed by dialysis. In growth assays, the purified protein showed specific antimicrobial activity against two different strains of Escherichia coli.

The Galleria mellonella larvae as an in vivo model for evaluation of Shigella virulence

Shigella spp. causing bacterial diarrhea and dysentery are human enteroinvasive bacterial pathogens that are orally transmitted through contaminated food and water and cause bacillary dysentery. Although natural Shigella infections are restricted to humans and primates, several smaller animal models are used to analyze individual steps in pathogenesis. No animal model fully duplicates the human response and sustaining the models requires expensive animals, costly maintenance of animal facilities, veterinary services and approved animal protocols. This study proposes the development of the caterpillar larvae of Galleria mellonella as a simple, inexpensive, informative, and rapid in-vivo model for evaluating virulence and the interaction of Shigella with cells of the insect innate immunity. Virulent Shigella injected through the forelegs causes larvae death. The mortality rates were dependent on the Shigella strain, the infectious dose, and the presence of the virulence plasmid. Wild-type S. flexneri 2a, persisted and replicated within the larvae, resulting in haemocyte cell death, whereas plasmid-cured mutants were rapidly cleared. Histology of the infected larvae in conjunction with fluorescence, immunofluorescence, and transmission electron microscopy indicate that S. flexneri reside within a vacuole of the insect haemocytes that ultrastructurally resembles vacuoles described in studies with mouse and human macrophage cell lines. Some of these bacteria-laden vacuoles had double-membranes characteristic of autophagosomes. These results suggest that G. mellonella larvae can be used as an easy-to-use animal model to understand Shigella pathogenesis that requires none of the time and labor-consuming procedures typical of other systems.

The upregulation of immune responses in tyrosine hydroxylase (TH) silenced Litopenaeus vannamei

Catecholamines (CAs) play a crucial role in maintaining physiological and immune homeostasis in invertebrates and vertebrates under stressful conditions. Tyrosine hydroxylase (TH) is the first and rate-limiting enzyme in CA synthesis. To develop an effective CA-related immunological defense system against stress and pathogen infection, various criteria, were evaluated in TH double-stranded (ds) RNA-injected white shrimp, Litopenaeus vannamei. Specifically, the relative transcript quantification of TH, dopamine β-hydroxylase (DBH), crustacean hyperglycemic hormone (CHH), and other immune-related genes; TH activity in the haemolymph; and the estimation of l-dihydroxyphenylalanine (l-DOPA), glucose, and lactate levels in the haemolymph were examined. TH depletion revealed a significant increase in the total haemocyte count; granular cells; semigranular cells; respiratory bursts (RBs, release of superoxide anion); superoxide dismutase (SOD) activity; phagocytic activity and clearance efficiency; and the expression of lipopolysaccharide and β-1,3-glucan-binding protein and peroxinectin, SOD, crustin, and lysozyme genes. In addition, the reduction of TH gene expression and activity was accompanied by a decline of phenoloxidase (PO) activity per granulocyte, lower glucose and lactate levels, and significantly low expression of DBH and CHH genes. However, the number of hyaline cells, activity of PO, RBs per haemocyte, and expression of POI and POII genes were not significantly different in the LvTH-silenced shrimp. Notably, the survival ratio of LvTH-silenced shrimp was significantly higher than that of shrimp injected with diethyl pyrocarbonate-water and nontargeting dsRNA when challenged with Vibrio alginolyticus. Therefore, the depletion of TH can enhance disease resistance in shrimp by upregulating specific immune parameters but downregulating the levels of carbohydrate metabolites.

The potential of the Galleria mellonella innate immune system is maximized by the co-presentation of diverse antimicrobial peptides

Antimicrobial peptides (AMPs) are ubiquitous components of the insect innate immune system. The model insect Galleria mellonella has at least 18 AMPs, some of which are still uncharacterized in terms of antimicrobial activity. To determine why G. mellonella secretes a repertoire of distinct AMPs following an immune challenge, we selected three different AMPs: cecropin A (CecA), gallerimycin and cobatoxin. We found that cobatoxin was active against Micrococcus luteus at a minimum inhibitory concentration (MIC) of 120 μm, but at 60 μm when co-presented with 4 μm CecA. In contrast, the MIC of gallerimycin presented alone was 60 μm and the co-presentation of CecA did not affect this value. Cobatoxin and gallerimycin were both inactive against Escherichia coli at physiological concentrations, however gallerimycin could potentiate the sublethal dose of CecA (0.25 μm) at a concentration of 30 μm resulting in 100% lethality. The ability of gallerimycin to potentiate the CecA was investigated by flow cytometry, revealing that 30 μm gallerimycin sensitized E. coli cells by inducing membrane depolarization, which intensified the otherwise negligible effects of 0.25 μm CecA. We therefore conclude that G. mellonella maximizes the potential of its innate immune response by the co-presentation of different AMPs that become more effective at lower concentrations when presented simultaneously.

Cloning and characterization of tyrosine hydroxylase (TH) from the pacific white leg shrimp Litopenaeus vannamei, and its expression following pathogen challenge and hypothermal stress

Tyrosine hydroxylase (TH) belongs to the biopterin-dependent aromatic amino acid hydroxylase enzyme family, and it represents the first and rate-limiting step in the synthesis of catecholamines that are required for physiological and immune process in invertebrates and vertebrates. Cloned Litopenaeus vannamei TH (LvTH), containing a short alpha helix domain, a catalytic core, a regulatory domain, a phosphorylation site and two potential N-linked glycosylation sites as presented in vertebrate and insect THs without acidic region and signal peptide cleavage sites at the amino-terminal, exhibited a similarity of 60.0-61.2% and 45.0-47.0% to that of invertebrate and vertebrate THs, respectively. Further, LvTH expression was abundant in gill and haemocytes determined by quantitative real-time PCR. L. vannamei challenged with Vibrio alginolyticus at 10(5) cfu shrimp(-1) revealed significant increase of LvTH mRNA expression in haemocytes within 30-120 min and in brain within 15-30 min followed with recuperation. In addition, shrimps exposed to hypothermal stress at 18 °C significantly increased LvTH expression in haemocytes and brain within 30-60 and 15-60 min, respectively. The TH activity and haemolymph glucose level (haemocytes-free) significantly increased in pathogen challenged shrimp at 120 min and 60 min, and in hypothermal stressed shrimp at 30-60 and 30 min, respectively. These results affirm that stress response initiates in the brain while haemocytes display later response. Further, the significant elevation of TH activity in haemolymph is likely to confer by TH that released from haemocytes. In conclusion, the cloned LvTH in our current study is a neural TH enzyme appears to be involved in the physiological and immune responses of whiteleg shrimp, L. vannamei suffering stressful stimulation.

Coevolution of parasitic fungi and insect hosts

Parasitic fungi and their insect hosts provide an intriguing model system for dissecting the complex co-evolutionary processes, which result in Red Queen dynamics. To explore the genetic basis behind host-parasite coevolution we chose two parasitic fungi (Beauveria bassiana and Metarhizium anisopliae, representing the most important entomopathogenic fungi used in the biological control of pest or vector insects) and two established insect model hosts (the greater wax moth Galleria mellonella and the red flour beetle Tribolium castaneum) for which sequenced genomes or comprehensive transcriptomes are available. Focusing on these model organisms, we review the knowledge about the interactions between fungal molecules operating as virulence factors and insect host-derived defense molecules mediating antifungal immunity. Particularly the study of the intimate interactions between fungal proteinases and corresponding host-derived proteinase inhibitors elucidated novel coevolutionary mechanisms such as functional shifts or diversification of involved effector molecules. Complementarily, we compared the outcome of coevolution experiments using the parasitic fungus B. bassiana and two different insect hosts which were initially either susceptible (Galleria mellonella) or resistant (Tribolium castaneum). Taking a snapshot of host-parasite coevolution, we show that parasitic fungi can overcome host barriers such as external antimicrobial secretions just as hosts can build new barriers, both within a relatively short time of coevolution.

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.

Lucimycin, an antifungal peptide from the therapeutic maggot of the common green bottle fly Lucilia sericata

We report the identification, cloning, heterologous expression and functional characterization of a novel antifungal peptide named lucimycin from the common green bottle fly Lucilia sericata. The lucimycin cDNA was isolated from a library of genes induced during the innate immune response in L. sericata larvae, which are used as therapeutic maggots. The peptide comprises 77 amino acid residues with a molecular mass of 8.2 kDa and a pI of 6.6. It is predicted to contain a zinc-binding motif and to form a random coil, lacking β-sheets or other secondary structures. Lucimycin was active against fungi from the phyla Ascomycota, Basidiomycota and Zygomycota, in addition to the oomycete Phytophtora parasitica, but it was inactive against bacteria. A mutant version of lucimycin, lacking the four C-terminal amino acid residues, displayed 40-fold lower activity. The activity of lucimycin against a number of highly-destructive plant pathogens could be exploited to produce transgenic crops that are resistant against fungal diseases.

Development of quantitative proteomics using iTRAQ based on the immunological response of Galleria mellonella larvae challenged with Fusarium oxysporum microconidia

Galleria mellonella has emerged as a potential invertebrate model for scrutinizing innate immunity. Larvae are easy to handle in host-pathogen assays. We undertook proteomics research in order to understand immune response in a heterologous host when challenged with microconidia of Fusarium oxysporum. The aim of this study was to investigate hemolymph proteins that were differentially expressed between control and immunized larvae sets, tested with F. oxysporum at two temperatures. The iTRAQ approach allowed us to observe the effects of immune challenges in a lucid and robust manner, identifying more than 50 proteins, 17 of them probably involved in the immune response. Changes in protein expression were statistically significant, especially when temperature was increased because this was notoriously affected by F. oxysporum 104 or 106 microconidia/mL. Some proteins were up-regulated upon immune fungal microconidia challenge when temperature changed from 25 to 37°C. After analysis of identified proteins by bioinformatics and meta-analysis, results revealed that they were involved in transport, immune response, storage, oxide-reduction and catabolism: 20 from G. mellonella, 20 from the Lepidoptera species and 19 spread across bacteria, protista, fungi and animal species. Among these, 13 proteins and 2 peptides were examined for their immune expression, and the hypothetical 3D structures of 2 well-known proteins, unannotated for G. mellonella, i.e., actin and CREBP, were resolved using peptides matched with Bombyx mori and Danaus plexippus, respectively. The main conclusion in this study was that iTRAQ tool constitutes a consistent method to detect proteins associated with the innate immune system of G. mellonella in response to infection caused by F. oxysporum. In addition, iTRAQ was a reliable quantitative proteomic approach to detect and quantify the expression levels of immune system proteins and peptides, in particular, it was found that 104 microconidia/mL at 37°C over expressed many more proteins than other treatments.

Heritable genome editing with CRISPR/Cas9 in the silkworm, Bombyx mori

We report the establishment of an efficient and heritable gene mutagenesis method in the silkworm Bombyx mori using modified type II clustered regularly interspaced short palindromic repeats (CRISPR) with an associated protein (Cas9) system. Using four loci Bm-ok, BmKMO, BmTH, and Bmtan as candidates, we proved that genome alterations at specific sites could be induced by direct microinjection of specific guide RNA and Cas9-mRNA into silkworm embryos. Mutation frequencies of 16.7-35.0% were observed in the injected generation, and DNA fragments deletions were also noted. Bm-ok mosaic mutants were used to test for mutant heritability due to the easily determined translucent epidermal phenotype of Bm-ok-disrupted cells. Two crossing strategies were used. In the first, injected Bm-ok moths were crossed with wild-type moths, and a 28.6% frequency of germline mutation transmission was observed. In the second strategy, two Bm-ok mosaic mutant moths were crossed with each other, and 93.6% of the offsprings appeared mutations in both alleles of Bm-ok gene (compound heterozygous). In summary, the CRISPR/Cas9 system can act as a highly specific and heritable gene-editing tool in Bombyx mori.

Galleria mellonella as an alternative model of Coxiella burnetii infection

Coxiella burnetii is a Gram-negative intracellular bacterium and is the causative agent of the zoonotic disease Q fever. Several rodent and non-human primate models of virulent phase I C. burnetii [Nine Mile (NM)I] have been developed, and have been used to determine the efficacy of antibiotics and vaccine candidates. However, there are several advantages to using insect models to study host–microbe interactions, such as reduced animal use, lowered cost and ease of manipulation in high containment. In addition, many laboratories use the avirulent phase II C. burnetii clone (NMII) to study cellular interactions and identify novel virulence determinants using genetic manipulation. We report that larvae of the greater wax moth, Galleria mellonella, were susceptible to infection with both C. burnetii NMI and NMII. Following subcutaneous infection, we report that intracellular bacteria were present within haemocytes and that larval death occurred in a dose-dependent manner. Additionally, we have used the model to characterize the role of the type 4 secretion system in C. burnetii NMII and to determine antibiotic efficacy in a non-mammalian model of disease.

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.

Choosing an appropriate infection model to study quorum sensing inhibition in Pseudomonas infections

Bacteria, although considered for decades to be antisocial organisms whose sole purpose is to find nutrients and multiply are, in fact, highly communicative organisms. Referred to as quorum sensing, cell-to-cell communication mechanisms have been adopted by bacteria in order to co-ordinate their gene expression. By behaving as a community rather than as individuals, bacteria can simultaneously switch on their virulence factor production and establish successful infections in eukaryotes. Understanding pathogen-host interactions requires the use of infection models. As the use of rodents is limited, for ethical considerations and the high costs associated with their use, alternative models based on invertebrates have been developed. Invertebrate models have the benefits of low handling costs, limited space requirements and rapid generation of results. This review presents examples of such models available for studying the pathogenicity of the Gram-negative bacterium Pseudomonas aeruginosa. Quorum sensing interference, known as quorum quenching, suggests a promising disease-control strategy since quorum-quenching mechanisms appear to play important roles in microbe-microbe and host-pathogen interactions. Examples of natural and synthetic quorum sensing inhibitors and their potential as antimicrobials in Pseudomonas-related infections are discussed in the second part of this review.

Heat shock affects host-pathogen interaction in Galleria mellonella infected with Bacillus thuringiensis

We report that Galleria mellonella larvae exposed to heat shock was more resistant to infection with entomopathogenic bacteria Bacillus thuringiensis. The insects were exposed to a temperature of 40°C for 30 min directly before injection of vegetative bacterial cells. It appeared that the kinetics of the immune response was affected in heat-shocked animals. The infection-induced antimicrobial activity of larval hemolymph was stronger in shocked animals in comparison to the non-shocked ones. Hemolymph proteins of molecular weight below 10 kDa, corresponding to the size of antimicrobial peptides, were responsible for this activity. Furthermore, the transcription level of genes encoding antimicrobial peptides: cecropin, gallerimycin, and galiomycin was increased in the fat bodies of insects exposed to heat shock before infection. On the contrary, the heat-shock treatment did not enhance expression of the metalloproteinase inhibitor-IMPI in the infected animals. The difference in the amount of antimicrobial peptides and, consequently, in the defense activity of insect hemolymph, persisted after the action of bacterial metalloproteinases, which are well-known virulence factors. Furthermore, peptides with antimicrobial activity in the hemolymph of infected larvae pre-exposed to heat shock appeared to be more resistant to proteolytic degradation both in vitro and in vivo. Our results point to the mechanism of cross-protection of thermal stress toward innate immune response.

Immune Signaling and Antimicrobial Peptide Expression in Lepidoptera

Many lepidopteran insects are agricultural pests that affect stored grains, food and fiber crops. These insects have negative ecological and economic impacts since they lower crop yield, and pesticides are expensive and can have off-target effects on beneficial arthropods. A better understanding of lepidopteran immunity will aid in identifying new targets for the development of specific insect pest management compounds. A fundamental aspect of immunity, and therefore a logical target for control, is the induction of antimicrobial peptide (AMP) expression. These peptides insert into and disrupt microbial membranes, thereby promoting pathogen clearance and insect survival. Pathways leading to AMP expression have been extensively studied in the dipteran Drosophila melanogaster. However, Diptera are an important group of pollinators and pest management strategies that target their immune systems is not recommended. Recent advances have facilitated investigation of lepidopteran immunity, revealing both conserved and derived characteristics. Although the general pathways leading to AMP expression are conserved, specific components of these pathways, such as recognition proteins have diverged. In this review we highlight how such comparative immunology could aid in developing pest management strategies that are specific to agricultural insect pests.

Gloverins of the silkworm Bombyx mori: structural and binding properties and activities

Gloverins are basic, glycine-rich and heat-stable antibacterial proteins (∼14- kDa) in lepidopteran insects with activity against Escherichia coli, Gram-positive bacteria, fungi and a virus. Hyalophora gloveri gloverin adopts a random coil structure in aqueous solution but has α-helical structure in membrane-like environment, and it may interact with the lipid A moiety of lipopolysaccharide (LPS). Manduca sexta gloverin binds to the O-specific antigen and outer core carbohydrate of LPS. In the silkworm Bombyx mori, there are four gloverins with slightly acidic to neutral isoelectric points. In this study, we investigate structural and binding properties and activities of B. mori gloverins (BmGlvs), as well as correlations between structure, binding property and activity. Recombinant BmGlv1-4 were expressed in bacteria and purified. Circular dichroism (CD) spectra showed that all four BmGlvs mainly adopted random coli structure (>50%) in aqueous solution in regardless of pH, but contained α-helical structure in the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), smooth and rough mutants (Ra, Rc and Re) of LPS and lipid A. Plate ELISA assay showed that BmGlvs at pH 5.0 bound to rough mutants of LPS and lipid A but not to smooth LPS. Antibacterial activity assay showed that positively charged BmGlvs (at pH 5.0) were active against E. coli mutant strains containing rough LPS but inactive against E. coli with smooth LPS. Our results suggest that binding to rough LPS is the prerequisite for the activity of BmGlvs against E. coli.

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.

Evolutionary history of x-tox genes in three lepidopteran species: origin, evolution of primary and secondary structure and alternative splicing, generating a repertoire of immune-related proteins

The proteins of the X-tox family have imperfectly conserved tandem repeats of several defensin-like motifs known as cysteine-stabilized αβ (CS-αβ) motifs. These immune-related proteins are inducible and expressed principally in hemocytes, but they have lost the antimicrobial properties of the ancestral defensins from which they evolved. We compared x-tox gene structure and expression in three lepidopteran species (Spodoptera frugiperda, Helicoverpa armigera and Bombyx mori). Synteny and phylogenetic analyses showed that the x-tox exons encoding CS-αβ motifs were phylogenetically closely related to defensin genes mapping to chromosomal positions close to the x-tox genes. We were able to define two groups of paralogous x-tox exons (three in Noctuids) that each followed the expected species tree. These results suggest that the ancestor of the three species already possessed an x-tox gene with at least two proto-domains, and an additional duplication/fusion should have occurred in the ancestor of the two noctuid species. An expansion of the number of exons subsequently occurred in each lineage. Alternatively, the proto x-tox gene possessed more copy and each group of x-tox domains might undergo concerted evolution through gene conversion. Accelerated protein evolution was detected in x-tox domains when compared to related defensins, concomitantly to multiplication of exons and/or the possible activation of concerted evolution. The x-tox genes of the three species have similar structural organizations, with repeat motifs composed of CS-αβ-encoding exons flanked by introns in phase 1. Diverse mechanisms underlie this organization: (i) the acquisition of new repeat motifs, (ii) the duplication of preexisting repeat motifs and (iii) the duplication of modules. A comparison of gDNA and cDNA structures showed that alternative splicing results in the production of multiple X-tox protein isoforms from the x-tox genes. Differences in the number and sequence of CS-αβ motifs in these isoforms were found between species, but also between individuals of the same species. Thus, our analysis of the genetic organization and expression of x-tox genes in three lepidopteran species suggests a rapid evolution of the organization of these genes.

Effect of nutrient deprivation on the susceptibility of Galleria mellonella larvae to infection

Larvae of Galleria mellonella are widely used to study the virulence of microbial pathogens and for assessing the potency of antimicrobial agents. This work examined the effect of nutritional deprivation on the ability of larvae to withstand infection in order to establish standardized conditions for the treatment of larvae for in vivo testing. Larvae deprived of food for seven days demonstrated an increased susceptibility to infection by the yeast Candida albicans. These larvae displayed a lower density of hemocytes compared with controls but hemocytes from starved and control larvae demonstrated the same ability to kill yeast cells. Hemolymph from starved larvae demonstrated reduced expression of a range of antimicrobial peptides (e.g., lipocalin) and immune proteins (e.g., apolipophorin and arylphorin). Deprivation of G. mellonella larvae of food leads to a reduction in the cellular and immune responses and an increased susceptibility to infection. Researchers utilizing these larvae should ensure adequate food is provided to larvae in order to allow valid comparisons to be made between results from different laboratories.

Manduca sexta gloverin binds microbial components and is active against bacteria and fungi

Hyalophora gloveri gloverin is a glycine-rich and heat stable antimicrobial protein with activity mainly against Escherichia coli. However, Spodoptera exigua gloverin is active against a Gram-positive bacterium but inactive against E. coli. In this study, we investigated expression profile, binding ability and antimicrobial activity of Manduca sexta gloverin (MsGlv). Msglv transcript was detected in several tissues of naïve larvae with higher levels in the midgut and testis. Expression of Msglv mRNA in larvae was up-regulated by active Spätzle-C108 and peptidoglycans (PGs) of E. coli and Staphylococcus aureus, and the activation was blocked by pre-injection of antibody to M. sexta Toll, suggesting that Msglv expression is regulated by the Toll-Spätzle pathway. Recombinant MsGlv bound to the O-specific antigen and outer core carbohydrate of lipopolysaccharide (LPS), Gram-positive lipoteichoic acid (LTA) and PG, and laminarin, but not to E. coli PG or mannan. MsGlv was active against Bacillus cereus, Saccharomyces cerevisiae and Cryptococcus neoformans, but was almost inactive against E. coli and S. aureus. Our results suggest that gloverins are active against some bacteria and fungi.

Role of DNA base excision repair in the mutability and virulence of Streptococcus mutans

The oral pathogen, Streptococcus mutans, possesses inducible DNA repair defences for protection against pH fluctuations and production of reactive oxygen metabolites such as hydrogen peroxide (H(2) O(2) ), which are present in the oral cavity. DNA base excision repair (BER) has a critical role in genome maintenance by preventing the accumulation of mutations associated with environmental factors and normal products of cellular metabolism. In this study, we examined the consequences of compromising the DNA glycosylases (Fpg and MutY) and endonucleases (Smx and Smn) of the BER pathway and their relative role in adaptation and virulence. Enzymatic characterization of the BER system showed that it protects the organism against the effects of the highly mutagenic lesion, 7,8-dihydro-8-oxo-2'-deoxyguanine (8-oxo-dG). S. mutans strains lacking a functional Fpg, MutY or Smn showed elevated spontaneous mutation frequencies; and, these mutator phenotypes correlated with the ability of the strains to survive killing by acid and oxidative agents. In addition, in the Galleria mellonella virulence model, strains of S. mutans deficient in Fpg, MutY and Smn showed increased virulence as compared with the parent strain. Our results suggest that, for S. mutans, mutator phenotypes, due to loss of BER enzymes, may confer an advantage to virulence of the organism.

Biogenesis of outer membrane vesicles in Serratia marcescens is thermoregulated and can be induced by activation of the Rcs phosphorelay system

Outer membrane vesicles (OMVs) have been identified in a wide range of bacteria, yet little is known of their biogenesis. It has been proposed that OMVs can act as long-range toxin delivery vectors and as a novel stress response. We have found that the formation of OMVs in the gram-negative opportunistic pathogen Serratia marcescens is thermoregulated, with a significant amount of OMVs produced at 22 or 30°C and negligible quantities formed at 37°C under laboratory conditions. Inactivation of the synthesis of the enterobacterial common antigen (ECA) resulted in a hypervesiculation phenotype, supporting the hypothesis that OMVs are produced in response to stress. We demonstrate that the phenotype can be reversed to wild-type (WT) levels upon the loss of the Rcs phosphorelay response regulator RcsB, but not RcsA, suggesting a role for the Rcs phosphorelay in the production of OMVs. MS fingerprinting of the OMVs provided evidence of cargo selection within wild-type cells, suggesting a possible role for Serratia OMVs in toxin delivery. In addition, OMV-associated cargo proved toxic upon injection into the haemocoel of Galleria mellonella larvae. These experiments demonstrate that OMVs are the result of a regulated process in Serratia and suggest that OMVs could play a role in virulence.

PhoP and OxyR transcriptional regulators contribute to Yersinia pestis virulence and survival within Galleria mellonella

The virulence of Yersinia pestis KIM6+ was compared with multiple isolates of Yersinia pseudotuberculosis and Yersinia enterocolitica toward larvae of the greater wax moth Galleria mellonella. Although Y. pestis and Y. pseudotuberculosis were able to cause lethal infection in G. mellonella, these species appeared less virulent than the majority of Y. enterocolitica strains tested. Y. pestis survived primarily within hemocytes of G. mellonella, and induced a strong antibacterial peptide response that lasted for at least 3 days in surviving larvae. Immunization with dead bacteria to induce an antibacterial response led to increased survival of the larvae following infection. Mutant strains lacking the either phoP or oxyR, which were less resistant to antibacterial peptides and hydrogen peroxide respectively, were attenuated and restoration of the wild-type genes on plasmids restored virulence. Our results indicate that the Y. pseudotuberculosis-Y. pestis lineage is not as virulent toward G. mellonella as are the majority of Y. enterocolitica isolates. Further, we have shown that G. mellonella is a useful infection model for analyzing Y. pestis host-pathogen interactions, and antibacterial peptide resistance mediated by phoP and reactive oxygen defense mediated by oxyR are important for Y. pestis infection of this insect.

Antimicrobial peptides: modes of mechanism, modulation of defense responses

Complicated schemes of classical breeding and their drawbacks, environmental risks imposed by agrochemicals, decrease of arable land, and coincident escalating damages of pests and pathogens have accentuated the necessity for highly efficient measures to improve crop protection. During co-evolution of host-microbe interactions, antimicrobial peptides (AMPs) have exhibited a brilliant history in protecting host organisms against devastation by invading pathogens. Since the 1980s, a plethora of AMPs has been isolated from and characterized in different organisms. Nevertheless the AMPs expressed in plants render them more resistant to diverse pathogens, a more orchestrated approach based on knowledge of their mechanisms of action and cellular targets, structural toxic principle, and possible impact on immune system of corresponding transgenic plants will considerably improve crop protection strategies against harmful plant diseases. This review outlines the current knowledge on different modes of action of AMPs and then argues the waves of AMPs’ ectopic expression on transgenic plants’ immune system.

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.

Functional divergence among silkworm antimicrobial peptide paralogs by the activities of recombinant proteins and the induced expression profiles

Antimicrobial peptides are small-molecule proteins that are usually encoded by multiple-gene families. They play crucial roles in the innate immune response, but reports on the functional divergence of antimicrobial peptide gene families are rare. In this study, 14 paralogs of antimicrobial peptides belonging to cecropin, moricin and gloverin families were recombinantly expressed in pET expression systems. By antimicrobial activity tests, peptides representing paralogs in the same family of cecropin and moricin families, displayed remarkable differences against 10 tested bacteria. The evolutionary rates were relatively fast in the two families, which presented obvious functional divergence among paralogs of each family. Four peptides of gloverin family had similar antimicrobial spectrum and activity against tested bacteria. The gloverin family showed similar antimicrobial function and slow evolutionary rates. By induced transcriptional activity, genes encoding active antimicrobial peptides were upregulated at obviously different levels when silkworm pupae were infected by three types of microbes. Association analysis of antimicrobial activities and induced transcriptional activities indicated that the antimicrobial activities might be positively correlated with induced transcriptional activities in the cecropin and moricin families. These results suggest that representative BmcecB6, BmcecD and Bmmor as the major effector genes have broad antimicrobial spectrum, strong antimicrobial activity and high microbe-induced expression among each family and maybe play crucial roles in eliminating microbial infection.

cDNA cloning and induction of tyrosine hydroxylase gene from the diamondback moth, Plutella xylostella

We cloned a full-length tyrosine hydroxylase cDNA from the integument of the diamondback moth, Plutella xylostella. In the phylogenetic tree, tyrosine hydroxylase (PxTH) clustered with the other lepidopteran THs. Serine residues in the PxTH sequence, namely Ser(24), Ser(31), Ser(35), Ser(53), and Ser(65), were predicted to be the target sites for phosphorylation based on PROSITE analysis. In particular, Ser(35) of PxTH is highly conserved across a broad phylogenetic range of animal taxa including rat and human. Western blot analysis using both PxTH-Ab1 and PxTH-Ab2 polyclonal antibodies verified the expression of PxTH in all life cycle stages of P. xylostella, namely the larval, pupal, and adult stages. To examine the possible immune function of PxTH in P. xylostella, PxTH gene expression was investigated by RT-PCR and western blotting analysis after challenging P. xylostella with bacteria. PxTH expression was elevated 1 h post-infection and was continued till 12 h of post-infection relative to control larvae injected with sterile water.