Plankton and marine aggregates as transmission vectors for V. aestuarianus 02/041 infecting the pacific oyster Crassostrea gigas

Vibrio aestuarianus is a bacterium related to mass mortality outbreaks of the Pacific oyster, Crassostrea gigas in Europe. In this study, the role of different planktonic substrates (phytoplankton cells, marine aggregates and chitin fragments) in mediating V. aestuarianus 02/041 infection of oysters was evaluated by controlled infection experiments. It was shown that phytoplankton cells and, to a greater extent, marine aggregates, significantly promote V. aestuarianus 02/041 intake by C. gigas maintained under stressful conditions in the laboratory. Such intake is associated with higher concentration of the pathogen in the bivalve hemolymph and compromised health status of infected oysters. In contrast, chitin particles do not play a significant role as transmission vector for V. aestuarianus 02/041 infecting its bivalve host. Interestingly, incorporation into marine aggregates foster extracellular proteases (ECPs) activity and a higher expression of bacterial virulence genes, that are potentially involved in bivalve infection. Results from this study contribute to elucidate transmission patterns of V. aestuarianus 02/041 to C. gigas that may be useful for the development of efficient measures to prevent and control oyster disease outbreaks.

Investigating bacterial infections in Galleria mellonella larvae: Insights into pathogen dissemination and behavior

The insect Galleria mellonella is an alternative animal model widely used for studying bacterial infections. It presents a wide range of advantages, including its low cost, easy maintenance and lack of ethical constraints. Among other features, their innate immune system is very similar to that of mammals. In this study, we dissected several larvae infected with important human pathogens: Mycobacterium abscessus, Staphylococcus aureus and Pseudomonas aeruginosa. By observing the fat body, gut, trachea, and hemolymph under the microscope, we were able to describe where bacteria tend to disseminate. We also quantified the number of bacteria in the hemolymph throughout the infection course and found significant differences between the different pathogens. With this work, we aimed to better understand the behavior and dissemination of bacteria in the infected larvae.

Host-pathogen interactions upon Candida auris infection: fungal behaviour and immune response in Galleria mellonella

Candida auris has globally emerged as a multidrug-resistant fungus linked to healthcare-associated outbreaks. There is still limited evidence on its virulence, pathogenicity determinants, and complex host-pathogen interactions. This study analyzes the in vivo fungal behaviour, immune response, and host-pathogen interactions upon C. auris infection compared to C. albicans and C. parapsilosis in G. mellonella. This was performed by immunolabelling fungal structures and larval plasmatocytes and using a quantitative approach incorporating bioinformatic morphometric techniques into the study of microbial pathogenesis. C. auris presents a remarkably higher immunogenic activity than expected at its moderate degree of tissue invasion. It induces a greater inflammatory response than C. albicans and C. parapsilosis at the expense of plasmatocyte nodule formation, especially in non-aggregative strains. It specifically invades the larval respiratory system, in a pattern not previously observed in other Candida species, and presents inter-phenotypic tissue tropism differences. C. auris filaments in vivo less frequently than C. albicans or C. parapsilosis mostly through pseudohyphal growth. Filamentation might not be a major pathogenic determinant in C. auris, as less virulent aggregative phenotypes form pseudohyphae to a greater extent. C. auris has important both interspecific and intraspecific virulence and phenotype heterogeneity, with aggregative phenotypes of C. auris sharing characteristics with low pathogenic species such as C. parapsilosis. Our work suggests that C. auris owns an important morphogenetic plasticity that distinguishes it from other yeasts of the genus. Routine phenotypic identification of aggregative or non-aggregative phenotypes should be performed in the clinical setting as it may impact patient management.

Acute melanization of silkworm hemolymph by peptidoglycans of the human commensal bacterium Cutibacterium acnes

Cutibacterium acnes is a pathogenic bacterium that cause inflammatory diseases of the skin and intervertebral discs. The immune activation induced by C. acnes requires multiple cellular responses in the host. Silkworm, an invertebrate, generates melanin by phenoloxidase upon recognizing bacterial or fungal components. Therefore, the melanization reaction can be used as an indicator of innate immune activation. A silkworm infection model was developed for evaluating the virulence of C. acnes, but a system for evaluating the induction of innate immunity by C. acnes using melanization as an indicator has not yet been established. Here we demonstrated that C. acnes rapidly causes melanization of the silkworm hemolymph. On the other hand, Staphylococcus aureus, a gram-positive bacterium identical to C. acnes, does not cause immediate melanization. Even injection of heat-killed C. acnes cells caused melanization of the silkworm hemolymph. DNase, RNase, and protease treatment of the heat-treated C. acnes cells did not decrease the silkworm hemolymph melanization. Treatment with peptidoglycan-degrading enzymes, such as lysostaphin and lysozyme, however, decreased the induction of melanization by the heat-treated C. acnes cells. These findings suggest that silkworm hemolymph melanization may be a useful indicator to evaluate innate immune activation by C. acnes and that C. acnes peptidoglycans are involved in the induction of innate immunity in silkworms.

Microbiomes of an oyster are shaped by metabolism and environment

Microbiomes can both influence and be influenced by metabolism, but this relationship remains unexplored for invertebrates. We examined the relationship between microbiome and metabolism in response to climate change using oysters as a model marine invertebrate. Oysters form economies and ecosystems across the globe, yet are vulnerable to climate change. Nine genetic lineages of the oyster Saccostrea glomerata were exposed to ambient and elevated temperature and PCO2 treatments. The metabolic rate (MR) and metabolic by-products of extracellular pH and CO2 were measured. The oyster-associated bacterial community in haemolymph was characterised using 16 s rRNA gene sequencing. We found a significant negative relationship between MR and bacterial richness. Bacterial community composition was also significantly influenced by MR, extracellular CO2 and extracellular pH. The effects of extracellular CO2 depended on genotype, and the effects of extracellular pH depended on CO2 and temperature treatments. Changes in MR aligned with a shift in the relative abundance of 152 Amplicon Sequencing Variants (ASVs), with 113 negatively correlated with MR. Some spirochaete ASVs showed positive relationships with MR. We have identified a clear relationship between host metabolism and the microbiome in oysters. Altering this relationship will likely have consequences for the 12 billion USD oyster economy.

Exosomal miR-224 contributes to hemolymph microbiota homeostasis during bacterial infection in crustacean

It is well known that exosomes could serve as anti-microbial immune factors in animals. However, despite growing evidences have shown that the homeostasis of the hemolymph microbiota was vital for immune regulation in crustaceans, the relationship between exosomes and hemolymph microbiota homeostasis during pathogenic bacteria infection has not been addressed. Here, we reported that exosomes released from Vibrio parahaemolyticus-infected mud crabs (Scylla paramamosain) could help to maintain the homeostasis of hemolymph microbiota and have a protective effect on the mortality of the host during the infection process. We further confirmed that miR-224 was densely packaged in these exosomes, resulting in the suppression of HSP70 and disruption of the HSP70-TRAF6 complex, then the released TRAF6 further interacted with Ecsit to regulate the production of mitochondrial ROS (mROS) and the expression of Anti-lipopolysaccharide factors (ALFs) in recipient hemocytes, which eventually affected hemolymph microbiota homeostasis in response to the pathogenic bacteria infection in mud crab. To the best of our knowledge, this is the first document that reports the role of exosome in the hemolymph microbiota homeostasis modulation during pathogen infection, which reveals the crosstalk between exosomal miRNAs and innate immune response in crustaceans.

Exosomes are small membrane vesicles of endocytic origin which are widely involved in the regulation of a variety of pathological processes in mammals. Yet, although the antibacterial function of exosomes has been discovered for many years, the relationship between exosomes and hemolymph microbiota homeostasis remains unknown. In the present study, we identified the miRNAs packaged by exosomes that were possibly involved in Vibrio parahaemolyticus infection by modulating hemolymph microbiota homeostasis in crustacean mud crab Scylla paramamosain. Moreover, it was found that miR-224 was densely packaged in exosomes after Vibrio parahaemolyticus challenge, resulting in the suppression of HSP70 and disruption of the HSP70-TRAF6 complex in recipient hemocytes, then the released TRAF6 was further interacted with Ecsit to regulate ROS and ALFs levels, which eventually affected hemolymph microbiota homeostasis to cope with pathogenic bacteria infection. Our finding is the first to reveal the relationship between exosomes and hemolymph microbiota homeostasis in animals, which shows a novel molecular mechanism of invertebrate resistance to pathogenic microbial infection.

Cellular Immune Response of an Endemic Lake Baikal Amphipod to Indigenous Pseudomonas sp

Studies of invertebrates have shown that the internal environment of crustaceans is not always sterile in normal conditions, and in many species, it can be populated by microorganisms even in the absence of any visible pathological processes in the body. This observation raises the question of whether genetically modified indigenous hemolymph microorganisms can be used for biotechnological purposes inside the crustacean either as local producers of some compounds or as sensors to physiological parameters. In this study, we tested the ability of the bacteria isolated from the hemolymph of the amphipod Eulimnogammarus verrucosus to hide from the cellular immune response of the host as the most important feature for their potential long-term application in vivo. 16S rDNA amplicon sequencing revealed five common bacterial genera in all analyzed samples of the amphipod hemolymph, among which Pseudomonas is most easily subjected to genome modification and, thus, the most prospective for biotechnological application. Cultivation of Pseudomonas gave us a number of strains undoubtedly derived from the amphipod hemolymph, and one of them (belonging to the Pseudomonas fluorescens group) was chosen for further tests. The primary culture of amphipod hemocytes was used to analyze the immunogenicity of the strain and showed a pronounced reaction of the immune cells to a high amount of the bacteria within six hours. This result indicates that modulation of cellular immune response to metabolically active bacterial cells is not mandatory for the survival and wide distribution of these microorganisms in the hemolymph of numerous amphipod individuals.

First record of a new microsporidium pathogenic to Gonipterus platensis in Brazil

Microsporidia are naturally occurring fungal-related parasites that can infect nearly all animal hosts, but their biocontrol potential of insect pests is routinely overlooked in agriculture and forestry. This research brings the first report describing the natural occurrence of a microsporidium causing disease in field-collected populations of the invasive eucalyptus snout beetle, Gonipterus platensis (Coleoptera: Curculionidae), a major destructive pest of eucalyptus plantations in Brazil. Adult beetles were collected during field surveys in commercial eucalyptus plantations in southern Brazil to be examined and dissected with typical symptoms to verify presence of microsporidian spores in haemolymph. From 14 plantations in different sites, the natural infection occurrence in these populations ranged from 0 to 65%, while a lab colony exhibited an infection incidence of 70%. Spore density in haemolymph of symptomatic insects averaged 2.1 (± 0.4) × 107 spores/beetle. Symptoms in infected adults were identified by an abnormal abdomen with malformation of the second pair of wings, impairing their flight activity. Electron transmission microscopy of the pathogen showed morphological features similar to species belonging to the genus Nosema or Vairimorpha. Phylogenetic analysis of the full-length small subunit ribosomal RNA gene suggests this pathogen's placement in the genus Vairimorpha, but with a sequence identity of ~ 94% with the nearest neighbours. The low level of sequence identity suggests this pathogen may represent a novel taxon in the genus and further requires whole genome sequencing for definitive taxonomic resolution. These findings provide insights on the natural occurrence of this novel pathogen of this invasive pest in Eucalyptus plantations in Brazil. Further studies are needed to determine potential of this microsporidium in the design of conservative or augmentative biological control programs for this invasive pest.

Dual proteomics of Drosophila melanogaster hemolymph infected with the heritable endosymbiont Spiroplasma poulsonii

Insects are frequently infected with heritable bacterial endosymbionts. Endosymbionts have a dramatic impact on their host physiology and evolution. Their tissue distribution is variable with some species being housed intracellularly, some extracellularly and some having a mixed lifestyle. The impact of extracellular endosymbionts on the biofluids they colonize (e.g. insect hemolymph) is however difficult to appreciate because biofluid composition can depend on the contribution of numerous tissues. Here we investigate Drosophila hemolymph proteome changes in response to the infection with the endosymbiont Spiroplasma poulsonii. S. poulsonii inhabits the fly hemolymph and gets vertically transmitted over generations by hijacking the oogenesis in females. Using dual proteomics on infected hemolymph, we uncovered a weak, chronic activation of the Toll immune pathway by S. poulsonii that was previously undetected by transcriptomics-based approaches. Using Drosophila genetics, we also identified candidate proteins putatively involved in controlling S. poulsonii growth. Last, we also provide a deep proteome of S. poulsonii, which, in combination with previously published transcriptomics data, improves our understanding of the post-transcriptional regulations operating in this bacterium.

Alterins Produced by Oyster-Associated Pseudoalteromonas Are Antibacterial Cyclolipopeptides with LPS-Binding Activity

Discovery after discovery, host-associated microbiota reveal a growing list of positive effects on host homeostasis by contributing to host nutrition, improving hosts' immune systems and protecting hosts against pathogens. In that context, a collection of oyster associated bacteria producing antibacterial compounds have been established to evaluate their role in non-host-derived immunity. Here, we described alterins; potent anti-Gram negative compounds produced by Pseudoalteromonas hCg-6 and hCg-42 isolated from different healthy oyster hemolymph. The strains hCg-6 and hCg-42 produce a set of at least seven antibacterial compounds, ranging from 926 to 982 Da structurally characterized as cyclolipopeptides (CLPs). Alterins share the same cationic heptapeptidic cycle connected via an amido bond to different hydrophobic hydrocarbon tails. Their MICs disclosed a potent antibacterial activity directed against Gram-negative bacteria including oyster and human pathogens that may confer a beneficial defense mechanism to the host but also represents an untapped source of new antibiotics. The alterins' mechanisms of action have been deciphered: after binding to lipopolysaccharides (LPS), alterins provoke a membrane depolarization and permeabilization leading to bacterial lysis. As hCg-6 and hCg-42 produced a set of natural derivatives, the structure/activity relationship linked to the carbon tail is clarified. We showed that the hydrocarbon tail determines the LPS-binding properties of alterins and consequently their antibacterial activities. Its length and saturation seem to play a major role in this interaction.

Pathogenesis-related genes of entomopathogenic fungi

All living things on Earth experience various diseases such as those caused by viruses, bacteria, and fungi. Insects are no exception to this rule, and fungi that cause disease in insects are called entomopathogenic fungi. These fungi have been developed as microbial insecticides and are used to control various pests. Generally, the mode of action of entomopathogenic fungi is divided into the attachment of conidia, germination, penetration, growth, and generation of secondary infectious conidia. In each of these steps, that entomopathogenic fungi use genes in a complex manner (specific or diverse) has been shown by gene knock-out and RNA-sequencing analysis. In this review, the information mechanism of entomopathogenic fungi was divided into six steps: (1) attachment of conidia to host, (2) germination and appressorium, (3) penetration, (4) fungal growth in hemolymph, (5) conidia production on host, and (6) transmission and dispersal. The strategy used by the fungi in each step was described at the genetic level. In addition, an approach for studying the mode of action of the fungi is presented.

Host Defense Effectors Expressed by Hemocytes Shape the Bacterial Microbiota From the Scallop Hemolymph

The interaction between host immune response and the associated microbiota has recently become a fundamental aspect of vertebrate and invertebrate animal health. This interaction allows the specific association of microbial communities, which participate in a variety of processes in the host including protection against pathogens. Marine aquatic invertebrates such as scallops are also colonized by diverse microbial communities. Scallops remain healthy most of the time, and in general, only a few species are fatally affected on adult stage by viral and bacterial pathogens. Still, high mortalities at larval stages are widely reported and they are associated with pathogenic Vibrio. Thus, to give new insights into the interaction between scallop immune response and its associated microbiota, we assessed the involvement of two host antimicrobial effectors in shaping the abundances of bacterial communities present in the scallop Argopecten purpuratus hemolymph. To do this, we first characterized the microbiota composition in the hemolymph from non-stimulated scallops, finding both common and distinct bacterial communities dominated by the Proteobacteria, Spirochaetes and Bacteroidetes phyla. Next, we identified dynamic shifts of certain bacterial communities in the scallop hemolymph along immune response progression, where host antimicrobial effectors were expressed at basal level and early induced after a bacterial challenge. Finally, the transcript silencing of the antimicrobial peptide big defensin ApBD1 and the bactericidal/permeability-increasing protein ApLBP/BPI1 by RNA interference led to an imbalance of target bacterial groups from scallop hemolymph. Specifically, a significant increase in the class Gammaproteobacteria and the proliferation of Vibrio spp. was observed in scallops silenced for each antimicrobial. Overall, our results strongly suggest that scallop antimicrobial peptides and proteins are implicated in the maintenance of microbial homeostasis and are key molecules in orchestrating host-microbiota interactions. This new evidence depicts the delicate balance that exists between the immune response of A. purpuratus and the hemolymph microbiota.

In Vitro and In Vivo Biological Activity of Berberine Chloride against Uropathogenic E. coli Strains Using Galleria mellonella as a Host Model

Berberine is an alkaloid of the protoberberine type used in traditional oriental medicine. Its biological activities include documented antibacterial properties against a wide variety of microorganisms; nonetheless, its use against Escherichia coli strains isolated from urinary infections has not yet been widely investigated in vivo. The emergence of antimicrobial resistance requires new therapeutic approaches to ensure the continued effectiveness of antibiotics for the treatment and prevention of urinary infections. Moreover, uropathogenic Escherichia coli (UPEC) has developed several virulence factors and resistance to routine antibiotic therapy. To this end, several in vitro and in vivo tests were conducted to assess the activity of berberine on uropathogenic E. coli strains. Galleria mellonella as an infection model was employed to confirm the in vivo translatability of in vitro data on berberine activity and its influence on adhesion and invasion proprieties of E. coli on human bladder cells. In vitro pre-treatment with berberine was able to decrease the adhesive and invasive UPEC ability. In vivo treatment increased the larvae survival infected with UPEC strains and reduced the number of circulating pathogens in larvae hemolymph. These preliminary findings demonstrated the efficacy and reliability of G. mellonella as in vivo model for pre-clinical studies of natural substances.

SpATF2 participates in maintaining the homeostasis of hemolymph microbiota by regulating dual oxidase expression in mud crab

Activating transcription factors 2 (ATF2) is a transcription factor of the members of ATF/CREB family that is phosphorylated and activated by the mitogen-activated protein kinase (MAPK) in responding to the stimulation of stimuli. In present study, SpATF2 from mud crab (Scylla paramamosain) was identified and studied. The open reading frame of SpATF2 with 2136 bp in length encodes a protein with 711 amino acids. The SpATF2 protein includes the putative zinc finger domain in the N-terminus and bZIP type DNA-binding domain in the C-terminal. Tissue distribution of SpATF2 transcripts showed that SpATF2 was ubiquitously expressed in all examined tissues of the untreated mud crabs, with the highest expression levels in muscle and hepatopancreas. The transcriptional level of SpATF2 was up-regulated in the hemocytes after Vibrio parahemolyticus or WSSV infection. Reporter gene assays indicated that SpATF2 could activate the expression of dual oxidase (SpDuox1) in S. paramamosain. The RNA interference (RNAi) of SpATF2 significantly decreased the expression of SpDuox1, and consequently reduced reactive oxygen species production thereby significantly increased the bacterial load in the hemolymph of mud crabs. Similarly, significant reduction in bacterial clearance of hemolymph was observed after the V. parahemolyticus infection in SpATF2 knockdown mud crabs. This study showed that SpATF2 played a vital role in maintaining homeostasis of the hemolymph microbiota through regulating the expression of dual oxidase of mud crab.

Identification of reference markers for characterizing honey bee (Apis mellifera) hemocyte classes

Cell mediated immunity of the honey bee (Apis mellifera) involves the activity of several hemocyte populations, currently defined by morphological features and lectin binding characteristics. The objective of the present study was to identify molecular markers capable of characterizing subsets of honey bee hemocytes. We developed and employed monoclonal antibodies with restricted reactions to functionally distinct hemocyte subpopulations. Melanizing cells, known as oenocytoids, were defined by an antibody to prophenoloxidase, aggregating cells were identified by the expression of Hemolectin, and phagocytic cells were identified by a marker expressed on granulocytes. We anticipate that this combination of antibodies not only allows for the detection of functionally distinct hemocyte subtypes, but will help to further the exploration of hematopoietic compartments, as well as reveal details of the honey bee cellular immune defense against parasites and microbes.

Heat shock proteins (HSP 90, 70, 60, and 27) in Galleria mellonella (Lepidoptera) hemolymph are affected by infection with Conidiobolus coronatus (Entomophthorales)

Invertebrates are becoming more popular models for research on the immune system. The innate immunity possessed by insects shows both structural and functional similarity to the resistance displayed by mammals, and many processes occurring in insect hemocytes are similar to those that occur in mammals. The humoral immune response in insects acts by melanization, clotting and the production of reactive oxygen species and antimicrobial peptides, while the cellular immunity system is based on nodulation, encapsulation and phagocytosis. An increasingly popular insect model in biological research is Galleria mellonella, whose larvae are sensitive to infection by the entomopathogenic fungus Conidiobolus coronatus, which can also be dangerous to humans. One group of factors that modulate the response of the immune system during infection in mammals are heat shock proteins (HSPs). The aim of this study was to investigate whether infection by C. coronatus in G. mellonella hemolymph is accompanied by an increase of HSP90, HSP70, HSP60 and HSP27. Larvae (five-day-old last instar) were exposed for 24 hours to fully-grown and sporulating fungus. Hemolymph was collected either immediately after termination of exposure (F24) or 24 hours later (F48). The concentration of the HSPs in hemolymph was determined using ELISA. Immunolocalization in hemocytes was performed using fluorescence microscopy and flow cytometry. HSP90, HSP70, HSP60 and HSP27 were found to be present in the G. mellonella hemocytes. HSP60 and HSP90 predominated in healthy insects, with HSP70 and HSP27 being found in trace amounts; HSP60 and HSP27 were elevated in F24 and F48, and HSP90 was elevated in F48. The fungal infection had no effect on HSP70 levels. These findings shed light on the mechanisms underlying the interaction between the innate insect immune response and entomopathogen infection. The results of this innovative study may have a considerable impact on research concerning innate immunology and insect physiology.

Source of hemolymph microbiota and their roles in the immune system of mud crab

Special innate immune mechanisms against pathogens are developed in marine invertebrates such as mud crab, which is also an economically important aquaculture species in many coastal countries. Hemolymph is a critical site in host immune response, but its source of microorganisms is less known. In this study, we provided a detailed investigation of the microorganisms inhabiting various body sites of healthy mud crabs, including hemolymph, midgut, gill, subcuticular epidermis and hepatopancreas. By using fluorescence microscopy and high-throughput sequencing of the bacterial 16S rRNA genes, various abundances and kinds of microorganisms were observed in the healthy mud crabs, of which some are potential pathogens to mud crab and human. The SourceTracker analysis and oral injection experiment confirm the hypothesis that hemolymph microorganisms are derived from the digestive systems of invertebrates with open circulatory systems, indicating that these microorganisms play vital roles in crab immune response. Moreover, physiological differences (gut length), behavioral characteristics (foraging behavior), diet preferences (herbivory), and/or sex hormones (testosterone) possibly determine the unique features of the crab-associated microbiota for both sexes. These findings also contribute to the development of appropriate microbial immunoenhancers, which has potential applications for improving quality and yield during crab aquaculture.

Effects of BDE-47 exposure on immune-related parameters of Mytilus galloprovincialis

The persistent pollutants polybrominated diphenyl ethers (PBDEs) have been demonstrated to produce several negative effects on marine organisms. Although Mytilus galloprovincialis was extensively studied as model system, the effects of PBDEs on the innate immune system of mussels remains unclear. In this study, except for the control treatment, specimens of M. galloprovincialis were fed with microalgae treated with increasing concentrations of PBDEs (maximum level 100 ng L^-1 of BDE-47 per day). BDE-47 treatment was maintained for 15 days and then the animals were fed with the same control diet, without contaminants, for 15 days. Samples of haemolymph (HL) were obtained at T0, T15 and T30 days of the experiment to evaluate different parameters related to immunity, such as neutral red retention time, and peroxidase, protease, antiprotease, lysozyme and bactericidal activities. BDE-47 exposure for 15 days affected both the stability of haemocytes and humoral parameters. In addition, the obtained results indicated that, at 30 days, after 15 days of culture without contaminant, the immune parameters were still affected, as some of them did not return to the basal levels, and others remained stimulated. Overall the results indicate that BDE-47 exposures at environmentally realistic levels may affect various aspects of immune function in M. galloprovincialis, acting as stressor that can compromise the general welfare.

Induction of DNA methyltransferase genes in Helicoverpa armigera following injection of pathogenic bacteria modulates expression of antimicrobial peptides and affects bacterial proliferation

Following pathogen attack in a host, widespread changes are induced in the host's gene expression, in particular those involved in the immune system, growth and survival. Epigenetic mechanisms have been suggested to be involved in the regulation of these changes through a number of mechanisms. DNA methylation is one of the important epigenetic processes that is carried out by DNA (cytosine-5) methyltransferase (DNMT) and alters expression of target genes. Here, we identified two putative sequences of DNMT (i.e. DNMT1 and DNMT2) from the transcriptome dataset of Helicoverpa armigera that showed high similarity to the homologous sequences in Bombyx mori. Domain architectures of DNMT1 and DNMT2 exhibit the unique pattern of DNMTs that highlights conserved function of these genes in different insects. To see if these genes play any role in bacterial infection, we challenged the fifth instar larvae of H. armigera by injecting Bacillus thuringiensis and Serratia marcescens cells into the hemolymph. Transcript levels of the DNMTs were analyzed by RT-qPCR. The results showed that the expression levels of DNMT1 and DNMT2 increased in the bacteria-injected larvae. Injection of the heat-killed bacteria also induced the expression of the DNMTs, but lower than that of the live bacteria. To determine whether these genes function during bacterial infection, we injected the inhibitor of DNMTs, 5-azacytidine (5-AZA), into the larvae and 24 h later, the bacterial cells were also injected into the larvae. Bacterial replication and larval mortality were analyzed in the treated and control insects. We found that 5-AZA reduced bacterial replication and also mortality of the bacterial-injected larvae regardless of the pathogenic bacterial species. Interestingly, the expression levels of antimicrobial peptides (AMPs) were also modulated following 5-AZA treatment. In conclusion, we showed that upregulation of the DNMTs in H. armigera following bacterial infections modulates AMPs and thereby affects the insect-bacteria interactions.

An IMD-like pathway mediates the intestinal immunity to modulate the homeostasis of gut microbiota in Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae)

Most animals have established the mutualistic interactions with their intestinal microbes which provide multiple benefits to their host physiology. However, the mechanisms behind hosts determine the load and composition of gut microbiota are still poorly understood outside dipteran insects. Here, the gene, encoding the NF-κB-like transcription factor Relish, being designated as RfRelish, was identified and analyzed in red palm weevil (RPW), Rhynchophorus ferrugineus Olivier. We revealed that the abundance of RfRelish transcripts in the fat body, hemolymph and gut are significantly higher than that in non-immunity-related tissues, and its expression level can be markedly induced by bacterial challenges. When RfRelish was silenced, the ability of individuals to clear the pathogenic bacteria in body cavity and gut was significantly compromised, suggesting that both the systemic and gut local immunity were impaired dramatically by RfRelish knockdown. Additionally, the silenced insects exhibited increased gut bacterial load, and the relative abundance of some gut bacteria was changed as compared to controls. Collectively, our findings demonstrate that the IMD-like pathway restricts the proliferation of gut bacteria and shapes the commensal community structure in the intestine of R. ferrugineus by mediating the secretion of antimicrobial peptides. We provide a striking example on how an insect pest maintains the homeostasis of gut microbiota via a conserved immune pathway without compromising the advantages of the mutualistic relationships.

Exposure to TiO2 nanoparticles induces shifts in the microbiota composition of Mytilus galloprovincialis hemolymph

It is now recognized that host microbiome, the community of microorganisms that colonize the animal body (e.g. microbiota) and their genomes, play an important role in the health status of all organisms, from nutrient processing to protection from disease. In particular, the complex, bilateral interactions between the host innate immune system and the microbiota are crucial in maintaining whole body homeostasis. The development of nanotechnology is raising concern on the potential impact of nanoparticles-NPs on human and environmental health. Titanium dioxide-nTiO₂, one of the most widely NP in use, has been shown to affect the gut microbiota of mammals and fish, as well as to potentially alter microbial communities. In the marine bivalve Mytilus galloprovincialis, nTiO₂ has been previously shown to interact with hemolymph components, thus resulting in immunomodulation. However, no information is available on the possible impact of NPs on the microbiome of marine organisms. Bivalves host high microbial abundance and diversity, and alteration of their microbiota, in both tissues and hemolymph, in response to stressful conditions has been linked to a compromised health status and susceptibility to diseases. In this work, the effects of nTiO₂ exposure (100 μg/L, 4 days) on Mytilus hemolymph microbiota were investigated by 16S rRNA gene-based profiling. Immune parameters were also evaluated. Although hemolymph microbiota of control and nTiO₂-treated mussels revealed a similar core composition, nTiO₂ exposure affected the abundance of different genera, with decreases in some (e.g. Shewanella, Kistimonas, Vibrio) and increases in others (e.g. Stenotrophomonas). The immunomodulatory effects of nTiO₂ were confirmed by the increase in the bactericidal activity of whole hemolymph. These represent the first data on the effects of NPs on the microbiome of marine invertebrates, and suggest that the shift in hemolymph microbiome composition induced by nTiO₂ may result from the interplay between the microbiota and the immune system.

Spp38 MAPK participates in maintaining the homeostasis of hemolymph microbiota in Scylla paramamosain

The p38 mitogen-activated protein kinases (MAPKs) are evolutionally conserved from yeasts to mammals, and are involved in the regulation of cells response to various extracellular stimuli. In this study, the p38 MAPK gene (designated as Spp38) of mud crab (Scylla paramamosain) was identified and studied. Spp38 contained the conserved Thr-Gly-Tyr (TGY) motif and a Ala-Thr-Arg-Trp (ATRW) substrate-binding site. Spp38 transcript was ubiquitously expressed in all tissues examined, with the highest expression found in muscle and hepatopancras. Quantitative real-time PCR revealed that Spp38 was upregulated in hemocytes and hepatopancras after infection with Vibrio parahemolyticus and Lipopolysaccharides (LPS). Reporter gene assays indicated that Spp38 activated the expression of anti-lipopolysaccharides (SpALF1 - SpALF6) in S. paramamosian. RNA interference (RNAi)-mediated knockdown of Spp38 or inhibition of Spp38 by SB203580 decreased the expression levels of SpALF1-6 and dual oxidase (SpDuox1 and SpDuox2) in S. paramamosian, which consequently reduced reactive oxygen species (ROS) production thereby significantly increasing the bacterial count in the hemolymph of mud crabs. Similarly, there was a significant reduction in bacterial clearance ability of hemolymph after Spp38 knockdown followed by V. parahemolyticus infection. Taken together, the current data indicated that Spp38 could play a vital role in maintaining the homeostasis of hemolymph microbiota in S. paramamosain.

Enterococcus faecalis YM0831 suppresses sucrose-induced hyperglycemia in a silkworm model and in humans

Hyperglycemia caused by excessive intake of sucrose leads to lifestyle-related diseases such as diabetes. Administration of a lactic acid bacterial strain to mice suppresses sucrose-induced hyperglycemia, but evidence for a similar effect in humans is lacking. Here we show that Enterococcus faecalis YM0831, identified using an in vivo screening system with silkworms, suppressed sucrose-induced hyperglycemia in humans. E. faecalis YM0831 also suppressed glucose-induced hyperglycemia in silkworms. E. faecalis YM0831 inhibited glucose uptake by the human intestinal epithelial cell line Caco-2. A transposon insertion mutant of E. faecalis YM0831, which showed decreased inhibitory activity against glucose uptake by Caco-2 cells, also exhibited decreased inhibitory activity against both sucrose-induced and glucose-induced hyperglycemia in silkworms. In human clinical trials, oral ingestion of E. faecalis YM0831 suppressed the increase in blood glucose in a sucrose tolerance test. These findings suggest that E. faecalis YM0831 inhibits intestinal glucose transport and suppresses sucrose-induced hyperglycemia in humans.

The hemolymph microbiome of insects

Hemolymph has long been recognized as a key mediator of nutritional and immunological homeostasis in insects, with the tacit understanding that hemolymph is a hostile environment for microorganisms, and microbiologically sterile in healthy insects. Recent research is overturning the conventional wisdom, and there is now overwhelming evidence that various non-pathogenic microorganisms can stably or transiently inhabit hemolymph in a diversity of insects. Most is known about Spiroplasma, especially in Drosophila species, and secondary symbionts of the Enterobacteriaceae, notably Hamiltonella defensa, in aphids. These bacteria require many nutrients, representing a likely drain on host nutritional resources, and they persist in the hemolymph by a combination of evasion and tolerance of insect immune effectors. These traits can be costly to the insect host. For some hemolymph microorganisms, these costs are balanced by other traits beneficial to the insect, notably protection against natural enemies mediated by specific toxins or competition for key nutrients. Three key priorities for future research are: to investigate the prevalence and taxonomic diversity of hemolymph microorganisms in insects; to establish the role of host nutritional and immune factors as determinants of the abundance and proliferation rates of hemolymph microorganisms; and to integrate the developing understanding of these microorganisms and their impacts (both costs and benefits) on insect nutrition and immune function into the wider study of insect physiology.

Effects of different dietary protein sources on the immunological and physiological responses of marron, Cherax cainii (Austin and Ryan, 2002) and its susceptibility to high temperature exposure

A two phased feeding trial was conducted to evaluate the effects of alternative protein sources on the immunophysiological responses of marron. During the phase I, marron were fed with five alternative protein supplemented diets for 90 days, while in phase II, the same marron were exposed to elevated temperature (30 °C) and their immunophysiological responses were investigated post exposure. Five isoproteic (crude protein 30%) and isoenergetic diets were prepared by containing fishmeal, poultry by-product meal, feather meal, lupin meal, and meat and bone meal as the main protein source. A hundred and fifty juvenile marron (Cherax cainii) of the average weight 9.09 ± 0.21 g were randomly distributed into 15 tanks (three replicates per feeding treatments). In the Phase I, general immune response parameters, such as, total haemocyte count (THC), proportion of hyaline cells, neutral red retention time (NRRT), phagocytic rate (PR), heamolymph bacteraemia, and condition indices of marron were investigated. The highest (P < 0.05) THC among dietary protein sources was obtained in marron fed with PbM at the end of experiment. Marron fed with FeM protein sources resulted in the highest survival rate followed by PbM fed group. Longer microvilli length (3.83 ± 0.18 μm) was demonstrated in marron fed with PbM diet. Diets containing FM and PbM protein sources revealed significantly (P < 0.05) lower number of microvilli/group than diets containing FeM and LM. The results demonstrated that different dietary protein sources in the marron diets did not detect significant (P > 0.05) change of the condition indices throughout the experiment period, however highest Hiw and Hid was recorded in marron fed with PBM at day 45. The PR of marron fed dietary protein from PbM did not change significantly after temperature exposure. Increased NRRT, PR and haemolymph bacteraemia was observed with dietary feeding of FM at the end of the trial. However, results revealed that PbM could be an alternative protein source for culture of marron as reflected in terms of increased THC, longer microvillus length and improved susceptibility to high temperature exposure. Overall, result could serve as useful baseline data in developing cost effective potential diets for marron aquaculture.

A novel LRR-only protein mediates bacterial proliferation in hemolymph through regulating expression of antimicrobial peptides in mollusk Chlamys farreri

Leucine-rich repeat (LRR)-only proteins are involved in innate immune responses through mediating protein-ligand or protein-protein interactions, yet the exact roles of most LRR-only proteins in invertebrates are not well documented. In the present study, a novel LRR-only protein (designated CfLRRop-7) was identified in Zhikong scallop Chlamys farreri. The full-length cDNA sequence of CfLRRop-7 was 1463 bp and contained an open reading frame of 1086 bp, which encoded a protein of 361 amino acids. Five LRR motifs with a conserved signature sequence LxxLxLxxNxL were identified in the predicted protein sequence. The expression of CfLRRop-7 was particularly high in hemocytes. The expression of CfLRRop-7 was relatively high in oocytes and embryos during the ontogenesis of scallops. CfLRRop-7 expression changed in hemocytes in response to stimulation with different microbes, including Vibrio splendidus, Staphylococcus aureus and Pichia pastoris. CfLRRop-7 recognized five kinds of ligands/agonists. CfLRRop-7 recombinant protein inhibited bacterial proliferation in hemolymph and induced lysozyme activity in serum. After knocking down CfLRRop-7, the mRNA expression of selected antimicrobial peptides was reduced. All these results indicated that CfLRRop-7 might be a potential pattern recognition receptor that recognizes various pathogen associated molecular patterns, and regulates antibacterial immunity in scallops.

Cation-dependent mannose-6-phosphate receptor functions as a pattern recognition receptor in anti-bacterial immunity of Marsupenaeus japonicus

The cation-dependent mannose-6-phosphate receptor (CD-MPR) is a member of the P-type lectin family. As a type I transmembrane glycoprotein, it functions in the delivery of newly synthesized acid hydrolases from the trans-Golgi network to endosomes for their subsequent transfer to the lysosome by binding the mannose-6-phosphate receptor-recognition moieties in the hydrolases. However, the functions of CD-MPR in immune responses are seldom reported. In the present study, we identified a CD-MPR-like molecule in Marsupenaeus japonicus and designed it as MjCD-MPR. It was significantly upregulated after challenge with Vibrio anguillarum at the mRNA and protein levels. Knockdown of MjCD-MPR resulted in a significant increase in the amount of V. anguillarum in the hemolymph of shrimp, which suggested that MjCD-MPR plays a role in shrimp antibacterial defense. The recombinant extracytoplasmic region of MjCD-MPR could bind gram-positive and gram-negative bacteria by interaction with peptidoglycan, lipopolysaccharide, and lipoteichoic acid. MjCD-MPR showed no direct bacteriostatic or bacteriocidal activity. Knockdown of MjCD-MPR decreased the expression levels of several antimicrobial peptides (Alf-C1, Alf-E1, Crustin I-2, and Crustin I-3), suggesting that MjCD-MPR promotes the expression of antimicrobial peptides in shrimp. In summary, working as a pattern recognition receptor, MjCD-MPR recognizes invading bacteria and triggers the expression of AMPs against bacterial infection in shrimp.

Dual oxidases participate in the regulation of hemolymph microbiota homeostasis in mud crab Scylla paramamosain

Dual oxidases (DUOXs) were originally identified as NADPH oxidases (NOXs), found to be associated with the reactive oxygen species (ROS) hydrogen peroxide (H₂O₂) production at the plasma membrane and crucial in host biological processes. In this study, SpDUOX1 and SpDUOX2 of mud crab (Scylla paramamosain) were identified and studied. Both SpDUOX1 and SpDUOX2 are transmembrane proteins, including an N-signal peptide region and a peroxidase homology domain in the extracellular region, transmembrane regions, and three EF (calcium-binding region) domains, a FAD-binding domain, and a NAD binding domain in the intracellular region. The SpDUOXs were expressed in all tissues examined, but mainly in hepatopancreas, heart, and mid-intestine. The expression of the SpDUOXs in the hemolymph of mud crabs was up-regulated after challenge with Vibrio parahemolyticus or LPS. RNA interference (RNAi) of the SpDUOXs resulted in reduced ROS production in hemolymph. The bacterial count increased in the hemolymph of mud crabs injected with SpDUOX1 or SpDUOX2-RNAi, while the bacterial clearance ability of hemolymph significantly reduced. At the phylum level, the phyla Bacteroidetes and Actinobacteria were significantly increased, while Proteobacteria were significantly reduced following SpDUOX2 knockdown. There was a significant increase in the relative abundance of the genera Marinomonas, Pseudoalteromonas, Shewanella, and Hydrogenoph in SpDUOX2 depleted mud crabs compared with the controls. Our current findings therefore indicated that SpDUOXs might play important roles in maintaining the homeostasis in the hemolymph microbiota of mud crab.

Clip domain prophenoloxidase activating protease is required for Ostrinia furnacalis Guenée to defend against bacterial infection

The prophenoloxidase (PPO) activating system in insects plays an important role in defense against microbial invasion. In this paper, we identified a PPO activating protease (designated OfPAP) containing a 1203 bp open reading frame encoding a 400-residue protein composed of two clip domains and a C-terminal serine protease domain from Ostrinia furnacalis. SignalP analysis revealed a putative signal peptide of 18 residues. The mature OfPAP was predicted to be 382 residues long with a calculated M_r of 44.8 kDa and pI of 6.66. Multiple sequence alignment and phylogenetic analysis indicated that OfPAP was orthologous to the PAPs in the other lepidopterans. A large increase of the transcript levels was observed in hemocytes at 4 h post injection (hpi) of killed Bacillus subtilis, whereas its level in integument increased continuously from 4 to 12 hpi in the challenged larvae and began to decline at 24 hpi. After OfPAP expression had been silenced, the median lethal time (LT₅₀) of Escherichia coli-infected larvae (1.0 day) became significantly lower than that of E. coli-infected wild-type (3.0 days, p < 0.01). A 3.5-fold increase in E. coli colony forming units occurred in larval hemolymph of the OfPAP knockdown larvae, as compared with that of the control larvae not injected with dsRNA. There were notable decreases in PO and IEARase activities in hemolymph of the OfPAP knockdown larvae. In summary, we have demonstrated that OfPAP is a component of the PPO activation system, likely by functioning as a PPO activating protease in O. furnacalis larvae.

The effect of entomopathogenic fungal culture filtrate on the immune response and haemolymph proteome of the large pine weevil, Hylobius abietis

The large pine weevil Hylobius abietis L. is a major forestry pest in 15 European countries, where it is a threat to 3.4 million hectares of forest. A cellular and proteomic analysis of the effect of culture filtrate of three entomopathogenic fungi (EPF) species on the immune system of H. abietis was performed. Injection with Metarhizium brunneum or Beauvaria bassiana culture filtrate facilitated a significantly increased yeast cell proliferation in larvae. Larvae co-injected with either Beauvaria caledonica or B. bassiana culture filtrate and Candida albicans showed significantly increased mortality. Together these results suggest that EPF culture filtrate has the potential to modulate the insect immune system allowing a subsequent pathogen to proliferate. Injection with EPF culture filtrate was shown to alter the abundance of protease inhibitors, detoxifing enzymes, antimicrobial peptides and proteins involved in reception/detection and development in H. abietis larvae. Larvae injected with B. caledonica culture filtrate displayed significant alterations in abundance of proteins involved in cellulolytic and other metabolic processes in their haemolymph proteome. Screening EPF for their ability to modulate the insect immune response represents a means of assessing EPF for use as biocontrol agents, particularly if the goal is to use them in combination with other control agents.

Evaluation of the immune responses of the brown mussel Perna perna as indicators of fecal pollution

The mussel Perna perna is an intertidal bivalve that is widely distributed, cultivated and consumed in South Africa, Brazil and Venezuela. Among marine resources, bivalve mollusks are one of the most impacted by anthropogenic pollution, as they can accumulate pathogenic bacteria and water pollutants. Hemocytes are molluscan defense cells, and their abundance and functions can be affected in response to contaminants, such as bacterial load. However, no previous study has investigated the immune response of P. perna hemocytes. The aim of this study was to evaluate several immune parameters in P. perna as indicators of fecal pollution in mussel hemolymph and in seawater. We collected mussels and adjacent seawater from beaches with different levels of fecal contamination in Rio de Janeiro state (Brazil): Vermelha Beach (VB); Icaraí Beach (IB); Urca Beach (UB); and Jurujuba Beach (JB). Hemocyte parameters (density, morphology, phagocytic activity and production of Reactive Oxygen Species - ROS) were evaluated using flow cytometry. We quantified Fecal Indicator Bacteria (FIB) in seawater by the multiple tubes technique for each beach and for hemolymph by the spread-plate technique. In agreement with historical evaluation of fecal contamination levels, UB presented the highest FIB abundance in seawater (thermotolerant coliforms, TEC = 1600 NMP 100 mL^-1), whereas VB exhibited the lowest (TEC = 17 NMP 100 mL^-1). UB mussels had six and eight times higher hemocyte density and phagocytic activity, respectively, than mussels from VB. Mussels from VB and IB presented a significantly lower number of total coliforms in hemolymph and a significantly higher relative internal complexity of hemocytes than those from UB and JB (p ≤ 0.01, PERMANOVA). ROS production by hemocytes was significantly lower in mussels from VB compared to those from JB (p = 0.04, ANOVA). Our results indicate a significant relationship between the level of fecal contamination in aquatic environments and the immune response of mussel hemocytes. Immune-related parameters may therefore be useful as indicators of bivalve health and environmental quality. Our flow cytometric analysis of P. perna hemocytes represents a new approach for studying Perna perna biology and might represent a novel tool for measuring organic pollution and water quality.

Antimicrobial activity of a serine proteinase inhibitor SPIPm5 from the black tiger shrimp Penaeus monodon

A two-domain Kazal-type serine proteinase inhibitor, SPIPm5, from Penaeus monodon was studied. Its transcript was expressed in all tissues tested including the hemocytes, stomach, gill, lymphoid organ, muscle, intestine and heart albeit less in hepatopancreas and eyestalk. The expression of SPIPm5 gene was also up-regulated by heat stress, white spot syndrome virus (WSSV) infection and yellow head virus (YHV) infection. Injection of recombinant rSPIPm5 protein into normal shrimp to mimic heat stress condition did not have or had little stimulating effect on the expression of other immune genes: crustinPm1, penaeidin3, penaeidin5, Hsp70, SPIPm2 and SPIPm5. Like some other proteinase inhibitors, the rSPIPm5 could inhibit the hemolymph proPO activity. In survival experiments, the rSPIPm5 could prolong the life of WSSV-infected shrimp similar to the effect of heat stress. The rSPIPm5 also helped the YHV-, Vibrio harveyi- and V. parahaemolyticus-infected shrimp survive longer. The increased endurance against microbial infection was due to the inhibitory effects presumably activated by rSPIPm5 on viral replication and bacterial growth but not the expression of antimicrobial peptides. Therefore, the SPIPm5 plays an important role in shrimp innate immunity against the viral and bacterial infection.

Rhipicephalus microplus infected by Metarhizium: unveiling hemocyte quantification, GFP-fungi virulence, and ovary infection

Hemocytes, cells present in the hemocoel, are involved in the immune response of arthropods challenged with entomopathogens. The present study established the best methodology for harvesting hemocytes from Rhipicephalus microplus and evaluated the number of hemocytes in addition to histological analysis from ovaries of fungus-infected females and tested the virulence of GFP-fungi transformants. Different centrifugation protocols were tested, and the one in which presented fewer disrupted cells and higher cell recovery was applied for evaluating the effect of Metarhizium spp. on hemocytes against R. microplus. After processing, protocol number 1 (i.e., hemolymph samples were centrifuged at 500×g for 3 min at 4 °C) was considered more efficient, with two isolates used (Metarhizium robertsii ARSEF 2575 and Metarhizium anisopliae ARSEF 549), both wild types and GFP, to assess their virulence. In the biological assays, the GFP-fungi were as virulent as wild types, showing no significant differences. Subsequently, hemocyte quantifications were performed after inoculation, which exhibited notable changes in the number of hemocytes, reducing by approximately 80% in females previously treated with Metarhizium isolates in comparison to non-treated females. Complementarily, 48 h after inoculation, in which hemolymph could not be obtained, histological analysis showed the high competence of these fungi to colonize ovary from ticks. Here, for the first time, the best protocol (i.e., very low cell disruption and high cell recovery) for R. microplus hemocyte obtaining was established aiming to guide directions to other studies that involves cellular responses from ticks to fungi infection.

Comparative 16SrDNA Gene-Based Microbiota Profiles of the Pacific Oyster (Crassostrea gigas) and the Mediterranean Mussel (Mytilus galloprovincialis) from a Shellfish Farm (Ligurian Sea, Italy)

The pacific oyster Crassostrea gigas and the Mediterranean mussel Mytilus galloprovincialis are two widely farmed bivalve species which show contrasting behaviour in relation to microbial diseases, with C. gigas being more susceptible and M. galloprovincialis being generally resistant. In a recent study, we showed that different susceptibility to infection exhibited by these two bivalve species may depend on their different capability to kill invading pathogens (e.g., Vibrio spp.) through the action of haemolymph components. Specific microbial-host interactions may also impact bivalve microbiome structure and further influence susceptibility/resistance to microbial diseases. To further investigate this concept, a comparative study of haemolymph and digestive gland 16SrDNA gene-based bacterial microbiota profiles in C. gigas and M. galloprovincialis co-cultivated at the same aquaculture site was carried out using pyrosequencing. Bacterial communities associated with bivalve tissues (hemolymph and digestive gland) were significantly different from those of seawater, and were dominated by relatively few genera such as Vibrio and Pseudoalteromonas. In general, Vibrio accounted for a larger fraction of the microbiota in C. gigas (on average 1.7-fold in the haemolymph) compared to M. galloprovincialis, suggesting that C. gigas may provide better conditions for survival for these bacteria, including potential pathogenic species such as V. aestuarianus. Vibrios appeared to be important members of C. gigas and M. galloprovincialis microbiota and might play a contrasting role in health and disease of bivalve species. Accordingly, microbiome analyses performed on bivalve specimens subjected to commercial depuration highlighted the ineffectiveness of such practice in removing Vibrio species from bivalve tissues.

Immune status of the spiny lobster Jasus edwardsii with tail fan necrosis

Tail fan necrosis (TFN), a disorder commonly found in some populations of commercially fished and cultured lobsters, is thought to be initiated by injuries caused by handling and containment. The unsightly appearance of affected lobster tails significantly lowers their commercial value. Knowledge about TFN is limited. In this study we describe the morphological features of TFN and apply 6 common methods for evaluating the immune status of wild-caught Australasian red spiny lobsters Jasus edwardsii with and without TFN. The disease was more frequent in uropods than in telsons of the tail fan, and more extensive on the ventral versus the dorsal surfaces of the tail fan. Missing appendages (i.e. antenna, pereiopod or pleopod) were significantly more common and greater in number for individual lobsters affected with TFN versus those without, possibly as a result of handling in the fishery or as an indirect effect of the disease. Two immune parameters, total haemocyte count and phenoloxidase activity in the haemocyte lysate supernatant (HLS), were significantly compromised in lobsters with TFN. No differences were found in the other immune parameters, i.e. haemocyte viability, haemolymph bacterial count and the protein content of haemolymph plasma and HLS. The results are consistent with injury sustained during prior capture and handling that initiates TFN in these natural caught lobsters. These results raise some potential concerns about the fitness of lobsters in natural populations that are affected by TFN, and some potential solutions are proposed.

Characterization and function of a tachylectin 5-like immune molecule in Penaeus monodon

Tachylectin5A and its homolog, tachylectin5B both contain a fibrinogen-related domain (FReD) and have been studied in horseshoe crabs, Tachypleus tridentatus and Carcinoscorpius rotundicauda and shown to be involved in host defense. Here, we demonstrate the presence of tachylectin5-like genes in shrimp, Penaeus monodon, designated as Penlectin5-1 (PL5-1) and Penlectin5-2 (PL5-2), which both contain a signal peptide and a single FReD with an acetyl group and a calcium binding sites and they are both structurally similar to horseshoe crab tachylectin/carcinolectin5. The PL5-1and PL5-2 transcript were expressed in various shrimp tissues in normal shrimp, and their expression was upregulated in tissues such as hemocytes and hindgut following challenge with pathogenic Vibrio harveyi. The PL5-2 protein was detected in various tissues as well as in cell-free hemolymph. The biological function of the PL5-2 protein is to recognize some Gram-positive and Gram-negative bacteria regardless whether they are non-pathogenic or pathogenic. They have hemagglutination activity on human erythrocyte and bacterial agglutination activity to both Gram negative and Gram positive bacteria. Possible binding sites of PL5-2 to bacteria could be at the N-acetyl moiety of the GlcNAc-MurNAc cell wall of the peptidoglycan since the binding could be inhibited by GlcNAc or GalNAC. The presence of PL5-2 protein in both circulating hemolymph and intestine, where host and microbes are usually interacting, may suggest that the physiological function of shrimp tachylectin-like proteins is to recognize and bind to invading bacteria to immobilize and entrap these microbes and subsequently clear them from circulation and the host body, and probably to control and maintain the normal flora in the intestine.

Larval honey bees infected with Nosema ceranae have increased vitellogenin titers as young adults

Nosema ceranae is a pervasive and widespread honey bee pathogen that is associated with colony declines and has recently been shown to infect larval honey bees. In adult bees, Nosema infection is known to alter levels of a key protein, vitellogenin (Vg), which is necessary for egg-laying in queens, brood food production in workers, and proper immune function in all female bees. We therefore tested the effects of larval worker infection on hemolymph Vg titers. In 1-day old adult workers that were infected as larvae with 10,000 (10 K) or 40,000 (40 K) live N. ceranae spores/bee, Vg titers were significantly elevated by + 83% and + 73%, respectively, as compared to controls. At 7 days of adult age, Vg remained significantly elevated (+ 68%) in 10 K treated workers as compared to control workers. Nosema infection decreased total hemolymph protein titers in 1 and 7-day old adult bees (-50% in the 10 K and 40 K treated bees). Bees infected as larvae also had a more queen-like sting morphology. They developed slightly but significantly fewer barbs on their stings (-7% in the 40K-treated bees). Higher Vg levels are associated with younger bees. Thus, elevated Vg levels could delay normal age polyethism and disrupt colony balance.

The spread of Vibrio parahaemolyticus in tissues of the Pacific white shrimp Litopenaeus vannamei analyzed by PCR and histopathology

V. parahaemolyticus are bacteria that cause the Acute Hepatopancreatic Necrosis Disease (AHPND), or Early Mortality Syndrome (EMS), in shrimp. To further understand the pathogenesis mechanisms of V. parahaemolyticus infection in shrimp, the spreading of this bacterium in various tissues was investigated. The spread of infection in shrimp that were exposed to seawater bacteria was studied by PCR and histopathology at 1 min, 1, 6, 12, 24, 48 and 72 h after exposure. The PCR results showed that V. parahaemolyticus was at its most widespread at 6 h after exposure, at which point V. parahaemolyticus was found in the gills, hepatopancreas, intestine, muscles, and hemolymph. However, examinations after 6 h of infection found only small amounts of V. parahaemolyticus in hepatopancreas and intestines. Histopathology of the hepatopancreas showed abnormalities on gross examination at 1 min-72 h after exposure. This study indicates that V. parahaemolyticus can spread quickly by using the hepatopancreas as the target tissue. After 6 h of infection, V. parahaemolyticus was eliminated by immune system while their toxins still caused damage to shrimp tissues.

Phylogenetic diversity and functional characterization of the Manila clam microbiota: a culture-based approach

According to the hologenome theory, the microbiota contributes to the fitness of the holobiont having an important role in its adaptation, survival, development, health, and evolution. Environmental stress also affects the microbiota and its capability to assist the holobiont in coping with stress factors. Here, we analyzed the diversity of cultivable bacteria associated with Manila clam tissues (mantle, gills, hemolymph) in two non-contaminated sites (Portugal and France) and one metal-contaminated site (Portugal). A total of 240 isolates were obtained. Representative isolates (n = 198) of the overall diversity were identified by 16S rDNA sequencing and subjected to functional characterization. Isolates affiliated with Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. Proteobacteria (mostly Pseudoalteromonadaceae and Vibrionaceae) were dominant in non-contaminated sites while Actinobacteria (mostly Microbacteriaceae) dominated in the metal-contaminated site. The main factor affecting the microbiota composition was contamination. No significant differences were observed between clam tissues and geographic regions. Several isolates tested positive for antibacterial activity, biofilm formation, protease, and siderophore production. The results show that the Manila clam harbors a diverse microbiota that may contribute to clam protection and overall fitness, as well as to its adaptation to stressful environments. In addition, the Manila clam microbiota is revealed as a promising source of novel probiotics with potential application in aquaculture.

Hemolymph proteins of Anopheles gambiae larvae infected by Escherichia coli

Anopheles gambiae is a major vector of human malaria and its immune system in part determines the fate of ingested parasites. Proteins, hemocytes and fat body in hemolymph are critical components of this system, mediating both humoral and cellular defenses. Here we assessed differences in the hemolymph proteomes of water- and E. coli-pricked mosquito larvae by a gel-LC-MS approach. Among the 1756 proteins identified, 603 contained a signal peptide but accounted for two-third of the total protein amount on the quantitative basis. The sequence homology search indicated that 233 of the 1756 may be related to defense. In general, we did not detect substantial differences between the control and induced plasma samples in terms of protein numbers or levels. Protein distributions in the gel slices suggested post-translational modifications (e.g. proteolysis) and formation of serpin-protease complexes and high Mr immune complexes. Based on the twenty-five most abundant proteins, we further suggest that major functions of the larval hemolymph are storage, transport, and immunity. In summary, this study provided first data on constitution, levels, and possible functions of hemolymph proteins in the mosquito larvae, reflecting complex changes occurring in the fight against E. coli infection.

A Spirochaete is suggested as the causative agent of Akoya oyster disease by metagenomic analysis

Mass mortality that is acompanied by reddish browning of the soft tissues has been occurring in cultured pearl oyster, Pinctada fucata martensii. The disease is called Akoya oyster disease (AOD). Although spreading pattern of the disease and transmission experiments suggest that the disease is infectious, the causative agent has not yet been identified. We used shotgun and 16S rRNA-based metagenomic analysis to identify genes that are present specifically in affected oysters. The genes found only in diseased oysters were mostly bacterial origin, suggesting that the causative agent was a bacterial pathogen. This hypothesis was supported by the inhibition of AOD development in naïve oysters injected with the hemolymph of diseased animals followed immediately with penicillin bath-administration. Further analyses of the hemolymph and mantle specifically and universally detected genes of bacteria that belong to phylum Spirochaetes in diseased pearl oysters but not in healthy oysters. By in situ hybridization or immunostaining, a Brachyspira-like bacterium was observed in the smears of hemolymph from affected oysters, but not from healthy oysters. Phylogenetic analysis using 16S rRNA sequences showed that the presumptive causative bacterium was outside of but most closely related to family Brachyspiraceae. We propose ‘Candidatus Maribrachyspira akoyae’ gen. nov, sp nov., for this bacterium.

Anopheles gambiae larvae mount stronger immune responses against bacterial infection than adults: evidence of adaptive decoupling in mosquitoes

BACKGROUND

The immune system of adult mosquitoes has received significant attention because of the ability of females to vector disease-causing pathogens while ingesting blood meals. However, few studies have focused on the immune system of larvae, which, we hypothesize, is highly robust due to the high density and diversity of microorganisms that larvae encounter in their aquatic environments and the strong selection pressures at work in the larval stage to ensure survival to reproductive maturity. Here, we surveyed a broad range of cellular and humoral immune parameters in larvae of the malaria mosquito, Anopheles gambiae, and compared their potency to that of newly-emerged adults and older adults.

RESULTS

We found that larvae kill bacteria in their hemocoel with equal or greater efficiency compared to newly-emerged adults, and that antibacterial ability declines further with adult age, indicative of senescence. This phenotype correlates with more circulating hemocytes and a differing spatial arrangement of sessile hemocytes in larvae relative to adults, as well as with the individual hemocytes of adults carrying a greater phagocytic burden. The hemolymph of larvae also possesses markedly stronger antibacterial lytic and melanization activity than the hemolymph of adults. Finally, infection induces a stronger transcriptional upregulation of immunity genes in larvae than in adults, including differences in the immunity genes that are regulated.

CONCLUSIONS

These results demonstrate that immunity is strongest in larvae and declines after metamorphosis and with adult age, and suggest that adaptive decoupling, or the independent evolution of larval and adult traits made possible by metamorphosis, has occurred in the mosquito lineage.

Starvation and Imidacloprid Exposure Influence Immune Response by Anoplophora glabripennis (Coleoptera: Cerambycidae) to a Fungal Pathogen

In several insect systems, fungal entomopathogens synergize with neonicotinoid insecticides which results in accelerated host death. Using the Asian longhorned beetle, Anoplophora glabripennis (Motschulsky), an invasive woodborer inadvertently introduced into North America and Europe, we investigated potential mechanisms in the synergy between the entomopathogenic fungus Metarhizium brunneum Petch and the insecticide imidacloprid. A potential mechanism underlying this synergy could be imidacloprid's ability to prevent feeding shortly after administration. We investigated whether starvation would have an impact similar to imidacloprid exposure on the mortality of fungal-inoculated beetles. Using real-time PCR to quantify fungal load in inoculated beetles, we determined how starvation and pesticide exposure impacted beetles' ability to tolerate or resist a fungal infection. The effect of starvation and pesticide exposure on the encapsulation and melanization immune responses of the beetles was also quantified. Starvation had a similar impact on the survival of M. brunneum-inoculated beetles compared to imidacloprid exposure. The synergy, however, was not completely due to starvation, as imidacloprid reduced the beetles' melanotic encapsulation response and capsule area, while starvation did not significantly reduce these immune responses. Our results suggest that there are multiple interacting mechanisms involved in the synergy between M. brunneum and imidacloprid.

Expression of the insect metalloproteinase inhibitor IMPI in the fat body of Galleria mellonella exposed to infection with Beauveria bassiana

The inducible metalloproteinase inhibitor (IMPI) discovered in Galleria mellonella is currently the only specific inhibitor of metalloproteinases found in animals. Its role is to inhibit the activity of metalloproteinases secreted by pathogenic organisms as virulence factors to degrade immune-relevant polypeptides of the infected host. This is a good example of an evolutionary arms race between the insect hosts and their natural pathogens. In this report, we analyze the expression of a gene encoding an inducible metalloproteinase inhibitor (IMPI) in fat bodies of the greater wax moth larvae Galleria mellonella infected with an entomopathogenic fungus Beauveria bassiana. We have used a natural infection, i.e. covering larval integument with fungal aerospores, as well as injection of fungal blastospores directly into the larval hemocel. We compare the expression of IMPI with the expression of genes encoding proteins with fungicidal activity, gallerimycin and galiomycin, whose expression reflects the stimulation of Galleria mellonella defense mechanisms. Also, gene expression is analyzed in the light of survival of animals after spore injection.

Immune priming and portal of entry effectors improve response to vibrio infection in a resistant population of the European abalone

Since 1997, populations of the European abalone Haliotis tuberculata suffer mass mortalities attributed to the bacterium Vibrio harveyi. These mortalities occur at the spawning season, when the abalone immune system is depressed, and when temperatures exceed 17 °C, leading to favorable conditions for V. harveyi proliferation. In order to identify mechanisms of disease resistance, experimental successive infections were carried out on two geographically distinct Brittany populations: one that has suffered recurrent mortalities (Saint-Malo) and one that has not been impacted by the disease (Molène). Furthermore, abalone surviving these two successive bacterial challenges and uninfected abalone were used for several post-infection analyses. The Saint-Malo population was found to be resistant to V. harveyi infection, with a survival rate of 95% compared to 51% for Molène. While in vitro quantification of phagocytosis by flow cytometry showed strong inhibition following the first infection, no inhibition of phagocytosis was observed following the second infection for Saint-Malo, suggesting an immune priming effect. Moreover, assays of phagocytosis of GFP-labelled V. harveyi performed two months post-infection show an inhibition of phagocytosis by extracellular products of V. harveyi for uninfected abalone, while no effect was observed for previously infected abalone from Saint-Malo, suggesting that the effects of immune priming may last upwards of two months. Detection of V. harveyi by qPCR showed that a significantly greater number of abalone from the susceptible population were positive for V. harveyi in the gills, indicating that portal of entry effectors may play a role in resistance to the disease. Collectively, these results suggest a potential synergistic effect of gills and hemolymph in the resistance of H. tuberculata against V. harveyi with an important involvement of the gills, the portal of entry of the bacteria.

Using Galleria mellonella as an Infection Model for Campylobacter jejuni Pathogenesis

Nonmammalian model systems of infection have been employed recently to study bacterial virulence. For instance, Galleria mellonella (the greater wax moth) has been shown to be susceptible to infection by many bacterial pathogens including the enteric pathogen Campylobacter jejuni. In contrast to the traditional animal models for C. jejuni such as the chick colonization model and ferret diarrheal model, the Galleria mellonella infection model has the advantages of lower cost, ease of use and no animal breeding is required. However, injecting the larvae with bacteria requires care to avoid killing of larvae, which could lead to misleading results. Here, we describe the infection of G. mellonella larvae by C. jejuni and how to record/interpret results.

A single-CRD C-type lectin is important for bacterial clearance in the silkworm

C-type lectins (CTLs) depend on the carbohydrate-recognition domain (CRD) to recognize carbohydrates by a Ca(2+)-dependent mechanism. In animals, CTLs play critical roles in pathogen recognition, activation of the complement system and signaling pathways. Immulectins (Dual-CRD CTLs) in lepidopteran are involved in recognizing pathogens. However, little is known about the immune-related functions of insect single-CRD CTLs. Here, we reported the characterization of C-type lectin-S3 (CTL-S3), a single-CRD CTL from the domesticated silkmoth Bombyx mori (Lepidoptera: Bombycidae). The ORF of CTL-S3 gene is 672 bp, which encodes a putative protein of 223 amino acids. CTL-S3 gene was expressed in a variety of tissues. Levels of CTL-S3 mRNA in fertilized eggs and whole larvae were elevated upon bacterial challenges. CTL-S3 was secreted to larval hemolymph. The recombinant protein (rCTL-S3) binds to bacterial cell wall components and bacteria. CTL-S3 inhibited the growth of Bacillus subtilis and caused agglutination of Staphylococcus aureus. More importantly, CTL-S3 facilitated the rapid clearance of Escherichia coli and Staphylococcus aureus from the body cavity of larvae. Taken together, our results suggested that CTL-S3 may function as an opsonin in larval hemolymph to enhance the clearance of pathogens.

The modulation of haemolymph arginine kinase on the extracellular ATP induced bactericidal immune responses in the Pacific oyster Crassostrea gigas

Arginine kinase is an important phosphagen kinase (PK) which plays an essential role in ATP buffering systems in invertebrates. In the present study, an arginine kinase (designated CgAK) was isolated by the lipopolysaccharide (LPS) affinity chromatography from the haemolymph of Crassostrea gigas. CgAK could directly bind to LPS in a concentration-dependent manner with the dissociation constant (Kd) of 2.46 × 10(-6) M. The interaction with LPS significantly decreased the ATP hydrolytic activity of CgAK, which in turn lead to the accumulation of ATP in vitro. The extracellular ATP stimulation could induce Ca(2+) influx, reactive oxygen species (ROS) production, and the release of lysosomal enzyme in the cellular immune response. In addition, ATP stimulation provoked the bactericidal activity towards Escherichia coli, and the scavenging ROS with N-acetyl-l-cysteine (NAC) abrogated the bactericidal activity, indicating that ATP stimulation could induce ROS-dependent antimicrobial activity in haemocytes. Collectively, the results demonstrated that the haemolymph CgAK could serve as an important purinergic regulator to modulate extracellular ATP, which might further have an important effect on the purinergic signaling-activated innate immune response of oyster.

Intracellular survival of Staphylococcus aureus during persistent infection in the insect Tenebrio molitor

Survival of bacteria within host cells and tissues presents a challenge to the immune systems of higher organisms. Escape from phagocytic immune cells compounds this issue, as immune cells become potential vehicles for pathogen dissemination. However, the duration of persistence within phagocytes and its contribution to pathogen load has yet to be determined. We investigate the immunological significance of intracellular persistence within the insect model Tenebrio molitor, assessing the extent, duration and location of bacterial recovery during a persistent infection. Relative abundance of Staphylococcus aureus in both intracellular and extracellular fractions was determined over 21 days, and live S. aureus were successfully recovered from both the hemolymph and within phagocytic immune cells across the entire time course. The proportion of bacteria recovered from within phagocytes also increased over time. Our results show that to accurately estimate pathogen load it is vital to account for bacteria persisting within immune cells.