Cytotoxicity and cytotoxic molecules in invertebrates

Three genes involved in the oxidative burst are closely linked in the genome of the snail, Biomphalaria glabrata

Allelic variation at the Cu-Zn superoxide dismutase (SOD1) locus has been shown to be associated with resistance of the snail, Biomphalaria glabrata, to infection by the trematode parasite, Schistosoma mansoni. SOD1 catalyses the production of hydrogen peroxide, a known cytotoxic component of the oxidative burst used in defence against pathogens. In our laboratory population of B. glabrata, the most resistant allele at SOD1 is over-expressed relative to the other two alleles. Because hydrogen peroxide also causes oxidative stress on host tissues, we hypothesised that over-expression of SOD1 might be compensated by epistatic interactions with other loci involved in oxidation-reduction (redox) pathways. Catalase, peroxiredoxins and glutathione peroxidases all degrade hydrogen peroxide. We tested whether alleles at each of these loci were in linkage disequilibrium with SOD1 in our population, as might be expected given strong epistatic selection. We found that SOD1, catalase (CAT) and a peroxiredoxin locus (PRX4) are in strong linkage disequilibrium in our population. We also found that these loci are tightly linked, within 1-2cM of each other, which explains the high linkage disequilibrium. This result raises the possibility that there is a linked cluster of redox genes, and perhaps other defence-relevant genes, in the B. glabrata genome. Whether epistatic interactions for fitness actually exist among these loci still needs to be tested. However the close physical linkage among SOD1, PRX4 and CAT, and subsequent high disequilibrium, makes such interactions a plausible hypothesis.

Looking for putative phenoloxidases of compound ascidians: haemocyanin-like proteins in Polyandrocarpa misakiensis and Botryllus schlosseri

Phenoloxidases (POs) and haemocyanins constitute a family of copper-containing proteins widely distributed among invertebrates. Both of them are able, under appropriate conditions, to convert polyphenols to quinones and induce cytotoxicity through the production of reactive oxygen species, a fundamental event in many immune responses. In ascidians, PO activity has been described and studied in both solitary and colonial species and the enzyme is involved in inflammatory and cytotoxic reactions against foreign cells or molecules, and in the formation of the cytotoxic foci which characterise the nonfusion reaction of botryllids. Expressed genes for two putative POs (CiPO1 and CiPO2) have been recently identified in C. intestinalis. In the present study, we determined the cDNA sequences of two haemocyanin-like proteins from two colonial ascidians: Botryllus schlosseri from the Mediterranean Sea and Polyandrocarpa misakiensis from Japan. Multiple sequence alignments evidenced the similarity between the above sequences and crustacean proPOs whereas the analysis of the three-dimensional structure reveals high similarity with arthropod haemocyanins which share common precursors with arthropod proPOs. Botryllus HLP grouped in the same cluster with Ciona POs, whereas Polyandrocarpa HLP clustered with arthropod haemocyanins; all of them share the full conservation of the six histidines at the two copper-binding sites as well as of other motifs, also found in arthropod haemocyanin subunits, involved in the regulation of enzyme activity. In situ hybridisation indicated that the genes are transcribed inside morula cells, a characteristic haemocyte type in ascidians where PO activity is located, at the beginning of their differentiation. These results represent a first attempt to identify candidate molecules responsible of the PO activity in compound ascidians.

The effects of the stress response on immune function in invertebrates: an evolutionary perspective on an ancient connection

Stress-induced changes in immune function occur in animals across phyla, and these effects are usually immunosuppressive. The function of this immunomodulation remains elusive; however, the existence of specialized receptors on immune cells suggests that it is adaptive. A comparative approach may provide a useful perspective. Although invertebrates have simpler endocrine/neuroendocrine systems and immune systems than vertebrates, they have robust stress responses that include the release of stress hormones/neurohormones. Stress hormones modify immune function in mollusks, insects, and crustaceans. As in vertebrates, the effects of stress hormones/neurohormones on invertebrate immune function are complex, and are not always immunosuppressive. They are context-, stressor-, time- and concentration-dependent. Stress hormone effects on invertebrate immune function may help to re-align resources during fight-or-flight behavior. The data are consistent with the hypothesis that stress hormones induce a reconfiguration of networks at molecular, cellular and physiological levels that allow the animal to maintain optimal immunity as the internal environment changes. This reconfiguration enhances some immune functions while suppressing others. Knowing the molecular details of these shifts will be critical for understanding the adaptive function of stress hormones on immune function.

Effects of Cu/Zn superoxide dismutase (sod1) genotype and genetic background on growth, reproduction and defense in Biomphalaria glabrata

Resistance of the snail Biomphalaria glabrata to the trematode Schistosoma mansoni is correlated with allelic variation at copper-zinc superoxide dismutase (sod1). We tested whether there is a fitness cost associated with carrying the most resistant allele in three outbred laboratory populations of snails. These three populations were derived from the same base population, but differed in average resistance. Under controlled laboratory conditions we found no cost of carrying the most resistant allele in terms of fecundity, and a possible advantage in terms of growth and mortality. These results suggest that it might be possible to drive resistant alleles of sod1 into natural populations of the snail vector for the purpose of controlling transmission of S. mansoni. However, we did observe a strong effect of genetic background on the association between sod1 genotype and resistance. sod1 genotype explained substantial variance in resistance among individuals in the most resistant genetic background, but had little effect in the least resistant genetic background. Thus, epistatic interactions with other loci may be as important a consideration as costs of resistance in the use of sod1 for vector manipulation.

Driving resistance genes into vector populations remains a promising but underused method for reducing transmission of vector-borne diseases. Understanding the genetic mechanisms governing resistance and how resistance is maintained in vector populations is essential for the development of resistant vectors as a means of eradicating vector-borne diseases. We investigated the utility of one gene (cytosolic copper-zinc superoxide dismutase - sod1) for driving resistance associated alleles into populations of the snail Biomphalaria glabrata, a vector of the trematode parasite of humans, Schistosoma mansoni. Under controlled laboratory conditions we found no evidence for costs of resistance associated with carrying the most resistant allele at sod1 (in terms of growth, fecundity, or mortality). However, we did find a strong effect of genetic background on how strongly sod1 genotype influences resistance. Thus, epistatic interactions with other loci may be as important a consideration as costs of resistance in the use of sod1 for vector manipulation in the field.

Immune activation decreases sperm viability in both sexes and influences female sperm storage

All animals are under the constant threat of pathogenic infection. However, little is known regarding the influence of acute infection on sperm viability, particularly in female insects. This information is crucial for our understanding of mating and immune system coevolution, considering that females store sperm and serve as the site of sperm competition. Using the fruitfly, Drosophila melanogaster, we examined the influence of infection on sperm viability and storage. Twenty-four hours after haemocoel inoculation with a pathogen mimic (peptidoglycan, PGN) both sexes exhibited reduced sperm viability, indicating that systemic immune activation played a significant role in gamete survival. Surprisingly, sperm death did not appear to result from a reproductive-immune system trade-off, considering that sperm survived 24 h in vitro once removed from their somatic resources. Instead, our results are most consistent with death owing to immune effector collateral damage. We also examined the potential for sexually transmitted pathogens to influence sperm storage. Females mated with 'infected' males (created by dipping genitalia into a PGN solution) exhibited a higher proportion of empty sperm stores 48 h after mating compared to their controls. Remarkably, these data indicate that females may increase their fitness by removing 'infected' ejaculates from storage over time.

How the insect pathogen bacteria Bacillus thuringiensis and Xenorhabdus/Photorhabdus occupy their hosts

Insects are the largest group of animals on earth. Like mammals, virus, fungi, bacteria and parasites infect them. Several tissue barriers and defense mechanisms are common for vertebrates and invertebrates. Therefore some insects, notably the fly Drosophila and the caterpillar Galleria mellonella, have been used as models to study host-pathogen interactions for several insect and mammal pathogens. They are excellent tools to identify pathogen determinants and host tissue cell responses. We focus here on the comparison of effectors used by two different groups of bacterial insect pathogens to accomplish the infection process in their lepidopteran larval host: Bacillus thuringiensis and the nematode-associated bacteria, Photorhabdus and Xenorhabdus. The comparison reveals similarities in function and expression profiles for some genes, which suggest that such factors are conserved during evolution in order to attack the tissue encountered during the infection process.

The cellular immune response of Daphnia magna under host-parasite genetic variation and variation in initial dose

In invertebrate-parasite systems, the likelihood of infection following parasite exposure is often dependent on the specific combination of host and parasite genotypes (termed genetic specificity). Genetic specificity can maintain diversity in host and parasite populations and is a major component of the Red Queen hypothesis. However, invertebrate immune systems are thought to only distinguish between broad classes of parasite. Using a natural host-parasite system with a well-established pattern of genetic specificity, the crustacean Daphnia magna and its bacterial parasite Pasteuria ramosa, we found that only hosts from susceptible host-parasite genetic combinations mounted a cellular response following exposure to the parasite. These data are compatible with the hypothesis that genetic specificity is attributable to barrier defenses at the site of infection (the gut), and that the systemic immune response is general, reporting the number of parasite spores entering the hemocoel. Further supporting this, we found that larger cellular responses occurred at higher initial parasite doses. By studying the natural infection route, where parasites must pass barrier defenses before interacting with systemic immune responses, these data shed light on which components of invertebrate defense underlie genetic specificity.

First report of two thioredoxin homologues in crustaceans: molecular characterization, genomic organization and expression pattern in swimming crab Portunus trituberculatus

Previously, we had reported two homologues of the thioredoxin (Trx) super-family (PtTrx1 and PtTrx2) identified from eyestalk and haemocytes cDNA library of swimming crab Portunus trituberculatus, respectively. It was the first report of two thioredoxin homologues from the same crustacean species. Here, we focused on the molecular characterization, genomic organization and expression pattern of PtTrx1 and PtTrx2. The full-length cDNA sequences of PtTrx1 and PtTrx2 were 739 and 1300 bp, encoding 105 and 133 amino acids, respectively. They both had a conserved CGPC active site and highly similar tertiary structures, which containing four β-sheets and four α-helixes. Specifically, PtTrx2 was encoded by a nuclear gene and its cellular localization was targeted to mitochondria by an N-terminal mitochondrial pre-sequence. Sequence analysis revealed PtTrx1 and PtTrx2 were encoded by different genomic locus. As the first analyzed genomic structure of PtTrxs in crustaceans, two introns with microsatellites were found in the open reading frame region of these genes. Quantitative real-time PCR analysis revealed the mRNA expression of PtTrx1 transcripts were mainly detected in gill, while, PtTrx2 in eyestalk and gill. The temporal expression levels of PtTrxs transcripts in haemocytes showed different expression patterns after challenge with Vibrio alginolyticus, Micrococcus luteus and Pichia pastoris. These results together indicate that PtTrxs should be involved in the responses to pathogen challenge of P. trituberculatus.

A shared role for RBF1 and dCAP-D3 in the regulation of transcription with consequences for innate immunity

Previously, we discovered a conserved interaction between RB proteins and the Condensin II protein CAP-D3 that is important for ensuring uniform chromatin condensation during mitotic prophase. The Drosophila melanogaster homologs RBF1 and dCAP-D3 co-localize on non-dividing polytene chromatin, suggesting the existence of a shared, non-mitotic role for these two proteins. Here, we show that the absence of RBF1 and dCAP-D3 alters the expression of many of the same genes in larvae and adult flies. Strikingly, most of the genes affected by the loss of RBF1 and dCAP-D3 are not classic cell cycle genes but are developmentally regulated genes with tissue-specific functions and these genes tend to be located in gene clusters. Our data reveal that RBF1 and dCAP-D3 are needed in fat body cells to activate transcription of clusters of antimicrobial peptide (AMP) genes. AMPs are important for innate immunity, and loss of either dCAP-D3 or RBF1 regulation results in a decrease in the ability to clear bacteria. Interestingly, in the adult fat body, RBF1 and dCAP-D3 bind to regions flanking an AMP gene cluster both prior to and following bacterial infection. These results describe a novel, non-mitotic role for the RBF1 and dCAP-D3 proteins in activation of the Drosophila immune system and suggest dCAP-D3 has an important role at specific subsets of RBF1-dependent genes.

The retinoblastoma protein (pRB) is a tumor suppressor protein known for its ability to repress transcription of E2F-dependent genes and induce cell cycle arrest. We have previously shown that RB proteins in Drosophila and human cells interact with the Condensin II subunit, CAP-D3, in an E2F-independent manner. Condensins promote condensation of chomosomes in mitosis. Our previous studies suggested that the Drosophila pRB and CAP-D3 homologs, RBF1 and dCAP-D3, co-localize on DNA and may share a function in cells that never undergo mitosis. In this study, we show that one non-mitotic function shared between RBF1 and dCAP-D3 is the regulation of many non-cell-cycle-related, clustered, and cell-type-specific transcripts including a conserved family of genes that are important for the immune response in the fly. In fact, results show that normal levels of dCAP-D3 and RBF1 expression are necessary for the ability of the fly to clear infection with human bacterial pathogens. This work demonstrates that dCAP-D3 proteins can regulate a unique subset of RBF1-dependent transcripts in vivo and identifies a novel role for both RBF1 and dCAP-D3 protein in activation of innate immune genes, which may be conserved in human cells.

Antimicrobial peptide gene induction, involvement of Toll and IMD pathways and defense against bacteria in the red flour beetle, Tribolium castaneum

Using Tribolium castaneum, we quantitatively investigated the induction of nine antimicrobial peptide (AMP) genes by live gram-negative bacteria (Escherichia coli and Enterobacter cloacae), gram-positive bacteria (Micrococcus luteus and Bacillus subtilis) and the budding yeast (Saccharomyces cerevisiae). Then, five representative AMP genes were selected, and the involvement of the Toll and IMD pathways in their induction by E. coli, M. luteus and S. cerevisiae was examined by utilizing RNA interference of either MyD88 or IMD. Results indicated: Robust and acute induction of three genes by the two bacterial species was mediated mainly by the IMD pathway; slow and sustained induction of one gene by the two bacteria was mediated mainly by the Toll pathway; induction of the remaining one gene by the two bacteria was mediated by both pathways; induction of the five genes by the yeast was mediated by the Toll and/or IMD pathways depending on respective genes. These results suggest that more promiscuous activation and usage of the two pathways may occur in T. castaneum than in Drosophila melanogaster. In addition, the IMD pathway was revealed to dominantly contribute to defense against two bacterial species, gram-negative E. cloacae and gram-positive B. subtilis that possesses DAP-type peptidoglycan.

Patterns of coral ecological immunology: variation in the responses of Caribbean corals to elevated temperature and a pathogen elicitor

Disease epizootics are increasing with climatic shifts, yet within each system only a subset of species are identified as the most vulnerable. Understanding ecological immunology patterns as well as environmental influences on immune defenses will provide insight into the persistence of a functional system through adverse conditions. Amongst the most threatened ecosystems are coral reefs, with coral disease epizootics and thermal stress jeopardizing their survival. Immune defenses were investigated within three Caribbean corals, Montastraea faveolata, Stephanocoenia intersepta and Porites astreoides, which represent a range of disease and bleaching susceptibilities. Levels of several immune parameters were measured in response to elevated water temperature and the presence of a commercial pathogen-associated molecular pattern (PAMP) - lipopolysaccharide (LPS) - as an elicitor of the innate immune response. Immune parameters included prophenoloxidase (PPO) activity, melanin concentration, bactericidal activity, the antioxidants peroxidase and catalase, and fluorescent protein (FP) concentration. LPS induced an immune response in all three corals, although each species responded differently to the experimental treatments. For example, M. faveolata, a disease-susceptible species, experienced significant decreases in bactericidal activity and melanin concentration after exposure to LPS and elevated temperature alone. Porites astreoides, a disease-resistant species, showed increased levels of enzymatic antioxidants upon exposure to LPS independently and increased PPO activity in response to the combination of LPS and elevated water temperature. This study demonstrates the ability of reef-building corals to induce immune responses in the presence of PAMPs, indicating activation of PAMP receptors and the transduction of appropriate signals leading to immune effector responses. Furthermore, these data address the emerging field of ecological immunology by highlighting interspecific differences in immunity and immunocompetences among Caribbean corals, which are reflected in their life-history characteristics, disease susceptibilities and bleaching-induced mortality.

Intramolecular cross-linking in the native JHBP molecule

Juvenile hormone binding protein (JHBP) acts as a shuttle, carrying one of the most crucial hormones for insect development to target tissues. We have found that although the JHBP molecule does not contain tryptophan residues, it exhibits a weak fluorescence maximum near 420nm upon excitation at 315nm. Gel filtration experiments performed in denaturing conditions and ESI-MS analyses excluded the possibility that some low molecular ligand was bound to the protein molecules. Further UV and CD spectroscopy studies, as well as immunoblotting, showed that the unusual JHBP optical properties were due to dityrosine intramolecular cross-linking. These bridges were detected both in native and recombinant protein molecules. We believe that in Galleria mellonella hemolymph the DT generation occurs via ROS-mediated oxidation leading to the formation of cross-linked JHBP monomers. MS analyses of peptides generated after JHBP proteolysis indicated, that the dityrosine bridge occurs between the Y128 and Y130 residues.

Short-term physiological effects of a xenobiotic mixture on the freshwater mussel Elliptio complanata exposed to municipal effluents

The aim of this study was to investigate the short-term effects of tertiary-treated municipal effluents on the freshwater mussel Elliptio complanata. Caged mussels were immersed during 2 weeks in a river located North of Montreal Island, upstream/downstream the outfall and in one reference site located at the beginning of the Rivière des Prairies. A selection of biomarkers was analyzed to depict changes on various physiological systems: general physiology (mussel viability, condition index and gonado-somatic index), immune status (hemocyte viability, cellularity, phagocytosis efficiency, NK-like cytotoxic activity and lysozyme activity), inflammation (cyclo-oxygenase activity), detoxification (glutathione-S-transferases activity) and vitellogenesis (alkali-labile phosphate level). The analysis of total and fecal coliform counts in water and of heterotrophic bacteria levels in mussel tissues showed that the bacteriological quality of the water strongly decreased from the reference site to the downstream site. This was correlated with a significant loss of weight and an increase of mussel mortality. Cellularity and phagocytosis efficiency were significantly increased in the downstream site compared to the reference site. Though not statistically significant, lysozyme activity was also increased. NK-like cytotoxicity, activity of the pro-inflammatory enzyme COX and the levels of ALP and MT were not significantly changed. Conversely, the municipal effluents induced a significant increase of GST activity in downstream site, indicating a stimulation of detoxification metabolism. Altogether, these results confirm that a short-term exposure to a mixture of bacterial and chemical compounds released by the wastewater treatment plant La Pinière induces adverse physiological effects in E. complanata, as observed with the modulation of immune response and induction of detoxification metabolism.

A comparative study of phenoloxidase activity in diseased and bleached colonies of the coral Acropora millepora

In scleractinian (hard) corals, immune responses involving phenoloxidase (PO) activity are known to play a role in coral wound healing, but there have been no studies investigating their roles in mitigating either disease or bleaching in an Indo-Pacific coral. PO activity induces the release of reactive oxygen species leading to a cytotoxic cellular environment, which enhances resistance against pathogens, but is also likely to compound oxidative stress induced during bleaching. Antioxidants such as melanin, whose synthesis is activated by PO activity, and peroxidase are potentially important for mitigating the effects of oxidative stress. Therefore, PO activity was investigated in healthy and diseased colonies of Acropora millepora. PO activity levels were compared among tissues bordering white syndrome lesions (WS) and at two locations (mid and outer) at increasing distances from lesions. Equivalent locations were sampled for PO activity on visibly healthy colonies. Additionally, PO and peroxidase activity were compared between severely bleached and healthy colonies of A. millepora. Overall, PO activity of diseased colonies was significantly lower than that of healthy colonies, but with relatively higher activity at the WS lesion border. Severely bleached colonies had significantly lower PO activity than healthy colonies, and peroxidase was also lower, but not significantly. Lower PO activity in unhealthy colonies supports earlier suggestions that lower immune activity leads to increased susceptibility to disease and bleaching. Additionally, low enzyme activity levels may indicate a depletion of colony resources. Increased PO activity at lesion borders in diseased colonies confirms the relative up-regulation of a key coral immune defense in response to WS in A. millepora.

Effects of tributyltin and benzo[a]pyrene on the immune-associated activities of hemocytes and recovery responses in the gastropod abalone, Haliotis diversicolor

Our previous study reports that short-term exposure to sublethal concentrations of benzo[a]pyrene (BaP) induces immunomodulation in the gastropod abalone, Haliotis diversicolor. In the present study, it was further observed that long-term chronic exposure to sublethal concentrations of BaP modulated the immunocompetence of abalones in terms of the change in activity of the antioxidant and immune associated parameters tested. In addition, the effect of tributyltin (TBT), another important genotoxicant in the aquatic environment, was investigated. Exposure of abalones to sublethal concentrations of TBT and BaP for 21 days resulted in significant decrease of total hemocyte count, phagocytosis, membrane stability and lysozyme activity. Conversely induction of extra and intra cellular superoxide generation, nitric oxide, nitric oxide synthase and myeloperoxidase activity was present when the abalones were exposed to TBT and BaP. Most of the immune associated parameters tested showed clear time dependent response to both toxicants. Within 14 days after the 21 day exposure to BaP, recovery was observed as evidenced by most of the parameters returning to their normal level. However, no recovery was observed within 14 days after the 21 day exposure to TBT as evidenced by continued elevation of intra cellular superoxide and nitrite production and decrease in THC, membrane stability and lysozyme activity. This suggested a prolonged TBT-induced impact on the immune reaction and possibly more damage than that caused by BaP. Overall the results suggest that chronic exposure to sublethal concentrations of TBT or BaP causes modulations in the immunocompetence of abalones with most of the immune associated parameters tested being stimulated, and this might be harmful to the host.

Pathways to immunity: temporal dynamics of the bumblebee (Bombus terrestris) immune response against a trypanosomal gut parasite

Immune response dynamics in insects from natural host-parasite associations are poorly understood, despite accumulating evidence of ecological immune phenomena in these systems. Using a gene discovery approach, we have identified genes relating to signalling, enzymatic processes and respiration that were up-regulated in the bumblebee, Bombus terrestris, during infection with the trypanosomatid parasite, Crithidia bombi. In addition, we have mapped dynamic changes in the temporal expression of these genes and three candidate antimicrobial peptide (AMP) immune genes, Abaecin, Defensin and Hymenoptaecin, from 1 to 24 h after C. bombi infection. We show that dynamic changes in expression occur for individual genes at distinct phases of the immune response to C. bombi that correspond to early, intermediate and late stages of infection.

Effects of vitamin E and beta-carotene on sperm competitiveness

Sperm are particularly prone to oxidative damage because they generate reactive oxygen species (ROS), have a high polyunsaturated fat content and a reduced capacity to repair DNA damage. The dietary compounds vitamin E and beta-carotene are argued to have antioxidant properties that help to counter the damaging effects of excess ROS. Here in, we tested the post-copulatory consequences for male crickets (Teleogryllus oceanicus) of dietary intake of these two candidate antioxidants. During competitive fertilisation trials, vitamin E, but not beta-carotene, singularly enhanced sperm competitiveness. However, the diet combining a high vitamin E dose and beta-carotene produced males with the most competitive ejaculates, possibly due to the known ability of beta-carotene to recycle vitamin E. Our results provide support for the idea that these two common dietary compounds have interactive antioxidant properties in vivo, by affecting the outcomes of male reproductive success under competitive conditions.

The effect of Habrobracon hebetor venom on the activity of the prophenoloxidase system, the generation of reactive oxygen species and encapsulation in the haemolymph of Galleria mellonella larvae

The cellular and humoral immune reactions in haemolymph of the wax moth Galleria mellonella larvae naturally injected by venom of ectoparasitic wasp Habrobracon hebetor were analyzed. A strong decline of phenoloxidase (PO) activity in the haemolymph and the number of haemocytes with PO activity of envenomated wax moth was observed. In addition, it has been shown that the rate of capsule melanization in the envenomated larvae was half that of the control. Also production of reactive oxygen species (ROS) in the haemolymph of envenomated larvae decreased. The obtained data casts light on the suppression of the main immune reactions in G. mellonella larvae during natural envenomation by H. hebetor.

Transcriptional analysis of a Photorhabdus sp. variant reveals transcriptional control of phenotypic variation and multifactorial pathogenicity in insects

Photorhabdus luminescens lives in a mutualistic association with entomopathogenic nematodes and is pathogenic for insects. Variants of Photorhabdus frequently arise irreversibly and are studied because they have altered phenotypic traits that are potentially important for the host interaction. VAR* is a colonial and phenotypic variant displaying delayed pathogenicity when directly injected into the insect, Spodoptera littoralis. In this study, we evaluated the role of transcriptomic modulation in determining the phenotypic variation and delayed pathogenicity of VAR* with respect to the corresponding wild-type form, TT01α. A P. luminescens microarray identified 148 genes as differentially transcribed between VAR* and TT01α. The net regulator status of VAR* was found to be significantly modified. We also observed in VAR* a decrease in the transcription of genes supporting certain phenotypic traits, such as pigmentation, crystalline inclusion, antibiosis, and protease and lipase activities. Three genes encoding insecticidal toxins (pit and pirB) or putative insecticidal toxins (xnp2) were less transcribed in VAR* than in the TT01α. The overexpression of these genes was not sufficient to restore the virulence of VAR* to the levels of ΤΤ01α, which suggests that the lower virulence of VAR* does not result from impaired toxemia in insects. Three loci involved in oxidative stress responses (sodA, katE, and the hca operon) were found to be downregulated in VAR*. This is consistent with the greater sensitivity of VAR* to H(2)O(2) and may account for the impaired bacteremia in the hemolymph of S. littoralis larvae observed with VAR*. In conclusion, we demonstrate here that some phenotypic traits of VAR* are regulated transcriptionally and highlight the multifactorial nature of pathogenicity in insects.

Immunocompetence of the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae): variation between developmental stages and sexes in populations in China

Immune defense imposes fitness costs as well as benefits, so organisms should optimize, not maximize, their immune function through their life cycle. We investigated this issue in the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae), which is a pine-killing invasive beetle in China, though it is usually considered as a secondary pest in its native range of North America. We hypothesized that pathogen pressure may affect these beetles differently throughout their life history. We measured the insect's immunocompetence throughout life, determining encapsulation ability and phenoloxidase activity in larval stages, pupae and adults. Pupae had the highest encapsulation ability, but encapsulation was not different between final instar larvae and adults. Phenoloxidase (PO) activity was highest in final instar larvae and pupae, followed by the second instar larvae and adults. Total phenoloxidase activity increased significantly from the second instar larval stage to pupae, and then decreased in adults. Although the second instar larvae had the lowest phenoloxidase activity, more than 90% of total PO existed in the hemolymph in the form of the active enzyme, as compared with pupae, in which over 60% of PO occurred as a proenzyme. Both active PO and total PO were much higher in females than in males, though no significant differences were detected between the encapsulation ability of male and female adults. This result suggests the existence of a sexual dimorphism of immunocompetence in D. valens adults. Variations in immunocompetence across developmental stages suggest that D. valens adopts diverse investment strategies in immunocompetence during different stages. Potential reasons for variation in immunocompetence among developmental stages and between the sexes of D. valens are discussed.

Comparative study of tumorigenesis and tumor immunity in invertebrates and nonmammalian vertebrates

Despite intense study in mammals, the different roles played by the immune system in detecting (immunosurveillance), controlling and remodeling (immunoediting) neoplasia, and perhaps in metastasis are not fully understood. In this review, I will present evidence of neoplasia and invasive malignancy, as well as tumor immunity in invertebrates and nonmammalian vertebrates. I will also present a comparative and evolutionary view of the complex interactions between neoplasia and the host immune system. Overall, I wish to go beyond the too simplistic dichotomy between invertebrates with innate immunity that are only affected with benign neoplasia and vertebrates with adaptive immunity that are affected by metastatic malignancies or cancer.

Porphyromonas gingivalis peptidoglycans induce excessive activation of the innate immune system in silkworm larvae

Porphyromonas gingivalis, a pathogen that causes inflammation in human periodontal tissue, killed silkworm (Bombyx mori, Lepidoptera) larvae when injected into the blood (hemolymph). Silkworm lethality was not rescued by antibiotic treatment, and heat-killed bacteria were also lethal. Heat-killed bacteria of mutant P. gingivalis strains lacking virulence factors also killed silkworms. Silkworms died after injection of peptidoglycans purified from P. gingivalis (pPG), and pPG toxicity was blocked by treatment with mutanolysin, a peptidoglycan-degrading enzyme. pPG induced silkworm hemolymph melanization at the same dose as that required to kill the animal. pPG injection increased caspase activity in silkworm tissues. pPG-induced silkworm death was delayed by injecting melanization-inhibiting reagents (a serine protease inhibitor and 1-phenyl-2-thiourea), antioxidants (N-acetyl-l-cysteine, glutathione, and catalase), and a caspase inhibitor (Ac-DEVD-CHO). Thus, pPG induces excessive activation of the innate immune response, which leads to the generation of reactive oxygen species and apoptotic cell death in the host tissue.

Genome-wide identification and expression analysis of serine proteases and homologs in the silkworm Bombyx mori

Background

Serine proteases (SPs) and serine proteases homologs (SPHs) are a large group of proteolytic enzymes, with important roles in a variety of physiological processes, such as cell signalling, defense and development. Genome-wide identification and expression analysis of serine proteases and their homologs in the silkworm might provide valuable information about their biological functions.

Results

In this study, 51 SP genes and 92 SPH genes were systematically identified in the genome of the silkworm Bombyx mori. Phylogenetic analysis indicated that six gene families have been amplified species-specifically in the silkworm, and the members of them showed chromosomal distribution of tandem repeats. Microarray analysis suggests that many silkworm-specific genes, such as members of SP_fam12, 13, 14 and 15, show expression patterns that are specific to tissues or developmental stages. The roles of SPs and SPHs in resisting pathogens were investigated in silkworms when they were infected by Escherichia coli, Bacillus bombysepticus, Batrytis bassiana and B. mori nucleopolyhedrovirus, respectively. Microarray experiment and real-time quantitative RT-PCR showed that 18 SP or SPH genes were significantly up-regulated after pathogen induction, suggesting that SP and SPH genes might participate in pathogenic microorganism resistance in B. mori.

Conclusion

Silkworm SP and SPH genes were identified. Comparative genomics showed that SP and SPH genes belong to a large family, whose members are generated mainly by tandem repeat evolution. We found that silkworm has species-specific SP and SPH genes. Phylogenetic and microarray analyses provide an overview of the silkworm SP and SPHs, and facilitate future functional studies on these enzymes.

Conventional and unconventional antimicrobials from fish, marine invertebrates and micro-algae

All eukaryotic organisms, single-celled or multi-cellular, produce a diverse array of natural anti-infective agents that, in addition to conventional antimicrobial peptides, also include proteins and other molecules often not regarded as part of the innate defences. Examples range from histones, fatty acids, and other structural components of cells to pigments and regulatory proteins. These probably represent very ancient defence factors that have been re-used in new ways during evolution. This review discusses the nature, biological role in host protection and potential biotechnological uses of some of these compounds, focusing on those from fish, marine invertebrates and marine micro-algae.

Identification of putative innate immune related genes from a cell line of the mosquito Aedes albopictus following bacterial challenge

We report identification of putative innate immune related genes from a cell line of the mosquito Aedes albopictus challenged with heat-killed bacteria. Using a subtractive hybridization and sequencing approach, we analyzed a total 309 expressed sequence tags (ESTs) which clustered in 40 contigs. Thirty-five percent of genes yielded homology to known immune genes corresponding to antimicrobial peptides (AMPs), pathogen-associated molecular patterns, protease and immune signaling cascades. Interestingly, most of the genes have not been previously described from this mosquito and thus represent a class of novel immune genes. Further, 25% sequences did not match to any known species in the non-redundant databases, appear to be specific to the mosquito A. albopictus and merit further study.

The role of melanization and cytotoxic by-products in the cellular immune responses of Drosophila against parasitic wasps

The cellular innate immune response of several species of Drosophila terminates with the encasement of large foreign objects within melanotic capsules comprised of several layers of adhering blood cells or hemocytes. This reaction is manifested by various Drosophila hosts in response to infection by endoparasitic wasps (i.e., parasitoids). Creditable assessments of the factor(s) causing, or contributing to, parasite mortality have long been considered as cytotoxic elements certain molecules associated with enzyme-mediated melanogenesis. However, observations that warrant additional or alternative considerations are those documenting parasitoid survival despite melanotic encapsulation, and those where parasitoids are destroyed with no evidence of this host response. Recent studies of the production of some reactive intermediates of oxygen and nitrogen during infection provide a basis for proposing that these molecules constitute important components of the immune arsenal of Drosophila. Studies of the virulence factors injected by female wasps during oviposition that suppress the host response will likely facilitate identification of the cytotoxic molecules as well as the cell-signaling pathways that regulate their synthesis.

Variation and covariation in infectivity, virulence and immunodepression in the host-parasite association Gammarus pulex-Pomphorhynchus laevis

Parasites often manipulate host immunity for their own benefit, either by exacerbating or suppressing the immune response and this may directly affect the expression of parasite virulence. However, genetic variation in immunodepression, which is a prerequisite to its evolution, and the relationship between immunodepression and virulence, have rarely been studied. Here, we investigated the variation among sibships of the acanthocephalan parasite, Pomphorhynchus laevis, in infecting and in immunodepressing its amphipod host, Gammarus pulex. We also assessed the covariation between infectivity, parasite-induced immune depression and host mortality (parasite virulence). We found that infectivity, the intensity of immunodepression and virulence were variable among parasite sibships. Infectivity and the level of immunodepression were not correlated across parasite sibships. Whereas infectivity was unrelated to host mortality, we found that gammarids that were exposed to the parasite sibships that immunodepressed their hosts the most survived better. This positive covariation between host survival and immunodepression suggests that gammarids exposed to the less immunodepressive parasites could suffer from damage imposed by a higher activity of the phenoloxidase.

Gene expression profiling during early response to injury and microbial challenges in the silkworm, Bombyx mori

To identify Bombyx mori genes involved in the early response to injury and microbial challenge, we performed genome-wide gene expression-profiling experiments using oligonucleotide DNA microarrays. Of approximately 23,000 genes examined, 465 displayed changes in mRNA expression levels. Of these, 306 were induced and 159 were repressed in response to injury (injection with phosphate buffer saline) or challenges by Gram-negative (Serratia marcescens), Gram-positive bacteria (Staphylococcus aureus), or fungus (Beauveria bassiana). Many of these differentially expressed genes can be assigned to specific functional groups of the innate immune response, including recognition, signaling, melanization and coagulation, and antimicrobial peptides. Seventeen percent of differentially expressed genes encode proteins with no obvious similarity to known functional domains. Of particular interest is a member of the juvenile hormone-binding protein family, which was highly induced by both injury and microbial challenges. The possible role of juvenile hormone in innate immunity is discussed.

Production of superoxides and nitric oxide generation in haemocytes of mussel Mytilus galloprovincialis (Lmk.) after exposure to cadmium: a possible involvement of Na(+)/H(+) exchanger in the induction of cadmium toxic effects

The present study investigates cadmium (Cd) ability to enhance superoxides (O(2-)) and nitric oxide (NO) production (as nitrites) in haemocytes of mussel Mytilus galloprovincialis as well as the possible involvement of Na(+)/H(+) exchanger (NHE) in the induction of NADPH oxidase and NO synthase activity. PMA, a well-known PKC-mediated NADPH oxidase as well as NO synthase stimulator was also used, in order to verify Cd effects on both O(2-) and NO generation. According to the results of the present study, micromolar concentrations of Cd (0.05, 5, 10 and 50 microM) seemed to enhance O(2-) and NO generation in haemocytes of mussels. Moreover, O(2-) and NO generation in haemocytes exposed to Cd could be enhanced by its ability to induce reactive oxygen species (ROS) but respiratory burst activation as well. Inhibition of NO synthase with 10 microM l-NAME, significantly attenuated Cd ability to enhance O(2-) production and diminished NO generation, thus leading to the suggestion that Cd toxic effects, started at concentration of 50 muM, could enhance NADPH oxidase and NO synthase stimulation in haemocytes of mussels. NHE seems to play a regulatory role in the induction of either O(2-) or NO generation in haemocytes exposed to the metal, since its inhibition with the use of 10 microM EIPA significantly decrease both O(2-) and NO production. The involvement of NHE in the induction of O(2-) and NO generation, probably via PKC-mediated NADPH oxidase and NO synthase activation, is likely to be crucial to haemocytes exposed to heavy metals, such as Cd.

Superoxide and hydrogen peroxide formation during enzymatic oxidation of DOPA by phenoloxidase

Generation of superoxide anion and hydrogen peroxide during enzymatic oxidation of 3-(3,4-dihydroxyphenyl)-DL-alanine (DOPA) has been studied. The ability of DOPA to react with O2*- has been revealed. EPR spectrum of DOPA-semiquinone formed upon oxidation of DOPA by O2*- was observed using spin stabilization technique of ortho-semiquinones by Zn2+ ions. Simultaneously, the oxidation of DOPA by O2*- was found to produce hydrogen peroxide (H2O2). The analysis of H2O2 formation upon oxidation of DOPA by O2*- using 1-hydroxy-3-carboxy-pyrrolidine (CP-H), and SOD as competitive reagents for superoxide provides consistent values of the rate constant for the reaction between DOPA and O2*- being equal to (3.4+/-0.6)x10(5) M(-1) s(-1). The formation of H2O2 during enzymatic oxidation of DOPA by phenoloxidase (PO) has been shown. The H2O2 production was found to be SOD-sensitive. The inhibition of H2O2 production by SOD was about 25% indicating that H2O2 is produced both from superoxide anion and via two-electron reduction of oxygen at the enzyme. The attempts to detect superoxide production during enzymatic oxidation of DOPA using a number of spin traps failed apparently due to high value of the rate constant for DOPA interaction with O2*-.

Review: Immunity mechanisms in crustaceans

Crustacean aquaculture represents a major industry in tropical developing countries. As a result of high culture densities and increasing extension of aquaculture farms, the presence of diseases has also increased, inducing economic losses. Invertebrates, which lack adaptive immune systems, have developed defense systems that respond against antigens on the surface of potential pathogens. The defense mechanisms of crustaceans depend completely on the innate immune system that is activated when pathogen-associated molecular patterns are recognized by soluble or by cell surface host proteins, such as lectins, antimicrobial, clotting, and pattern recognition proteins, which, in turn, activate cellular or humoral effector mechanisms to destroy invading pathogens. This work is aimed at presenting the main characteristics of the crustacean proteins that participate in immune defense by specific recognition of carbohydrate containing molecules, i.e. glycans, glycolipids, glycoproteins, peptidoglycans, or lipopolysaccharides from Gram-negative and Gram-positive bacteria, viruses, or fungi. We review some basic aspects of crustacean effector defense processes, like agglutination, encapsulation, phagocytosis, clottable proteins, and bactericidal activity, induced by these carbohydrate-driven recognition patterns.

Helicoverpa armigera (Lepidoptera: Noctuidae) larvae that survive sublethal doses of nucleopolyhedrovirus exhibit high metabolic rates

To determine the effect of sublethal doses of Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearSNPV) on the metabolic rate of H. armigera, the respiration rates of third instar H. armigera larvae inoculated with sublethal doses of HearSNPV were evaluated. Respiration rates, measured as the rate of CO(2) production (VCO(2)), were recorded daily using closed-system respirometry. By 4 days post-inoculation (dpi), the metabolic rates of LD(25) or LD(75) survivors were significantly higher than that of uninoculated controls. When dose data were pooled, the VCO(2) values of larvae that survived inoculation (0.0288mlh(-1)), the uninoculated controls (0.0250mlh(-1)), and the larvae that did not survive inoculation (0.0199mlh(-1)) differed significantly from one another. At 4dpi, the VCO(2) of the uninoculated controls were significantly lower than the VCO(2) of inoculation survivors, but significantly higher than the VCO(2) of inoculation non-survivors. Inoculation survivors may have had high metabolic rates due to a combination of viral replication, organ damage, and an energy-intensive induced cellular immune response. The high 4dpi metabolic rate of inoculation survivors may reflect an effective immune response and may be seen as the metabolic signature of larvae that are in the process of surviving inoculation with HearSNPV.

The veterinary drug ivermectin influences immune response in the yellow dung fly (Scathophaga stercoraria)

Phenoloxidase (PO) is a key enzyme involved in the immune response of insects. We show that egg-to-adult exposure to residues of 0.001, but not 0.0005 mgkg(-1) ivermectin elevated PO activity in yellow dung flies (Scathophaga stercoraria) developing in cattle dung. Fly fat content was unaffected by the treatments. Therefore, the response of PO was a direct effect of ivermectin and not an indirect one caused by an alteration in body 'condition'. This supports the non-intuitive conclusion that flies surviving exposure to faecal residues may have enhanced immune function. To our knowledge, this is the first study to assess the effects on PO activity of insecticidal residues in livestock dung. The non-target effects of such residues are of wide interest, given the global use of veterinary products.

Reactive oxygen species as universal constraints in life-history evolution

Evolutionary theory is firmly grounded on the existence of trade-offs between life-history traits, and recent interest has centred on the physiological mechanisms underlying such trade-offs. Several branches of evolutionary biology, particularly those focusing on ageing, immunological and sexual selection theory, have implicated reactive oxygen species (ROS) as profound evolutionary players. ROS are a highly reactive group of oxygen-containing molecules, generated as common by-products of vital oxidative enzyme complexes. Both animals and plants appear to intentionally harness ROS for use as molecular messengers to fulfil a wide range of essential biological processes. However, at high levels, ROS are known to exert very damaging effects through oxidative stress. For these reasons, ROS have been suggested to be important mediators of the cost of reproduction, and of trade-offs between metabolic rate and lifespan, and between immunity, sexual ornamentation and sperm quality. In this review, we integrate the above suggestions into one life-history framework, and review the evidence in support of the contention that ROS production will constitute a primary and universal constraint in life-history evolution.

Mass culture and characterization of tumor cells from a naturally occurring invertebrate cancer model: applications for human and animal disease and environmental health

On the northeastern coast of the United States and Canada, Mya arenaria, the soft shell clam, develops a diffuse, hemopoetic tumor (a fatal leukemia-like cancer) resulting from inactivation of p53-like family member proteins.These malignant cells provide a model for an unrelated set of human cancer cells that are also characterized by mortalin-based cytoplasmic sequestration of wild-type p53 tumor suppressor protein (mortalin is the mitochondrial Hsp70 protein). Here we describe methods for mass culture and long-term storage of tumor cells from this cancer. These are the first successful efforts at maintaining malignant cells from any marine invertebrate in vitro. Following passage (subculture), these cultures undergo transition from primary cultures to non-immortalized cell lines that continue to proliferate and do not re-differentiate the normal hemocyte phenotype. We also characterize normal clam hemocytes and the pathology of cancerous clam hemocytes in vitro and in vivo using light and electron microscopy, cyto- and immunocytochemistry, molecular biology, and a phagocytosis assay. Our protocols provide biomedical and environmental researchers with ready access to this naturally occurring cancer model. We discuss the clam cancer model regarding (a) human health and disease; (b) animal health, disease, and aquaculture; (c) environmental health monitoring; and (d) future research directions.

Induced cell proliferation in putative haematopoietic tissues of the sea star, Asterias rubens (L.)

The coelomic fluid of the echinoderm Asterias rubens possesses large populations of circulating coelomocytes. This study aimed to expand the knowledge about the haematopoietic sources of these cells. Injection of the immune-stimulating molecules lipopolysaccharide (LPS) and concanavalin A (ConA) resulted in an increase in coelomocytes. To investigate if these molecules induce cell proliferation in putative haematopoietic tissues (HPTs), short-term exposure of the substitute nucleotide 5-bromo-2'-deoxyuridine (BrdU) was conducted. Immunohistochemical analysis, using fluorescein-labelled antibodies to trace BrdU, showed pronounced cell division in the coelomic epithelium and axial organ. In the pyloric caeca, not considered as an HPT, proliferation was not detected. BrdU labelling of monolayers of cells obtained by collagenase treatment of coelomic epithelium, axial organ and Tiedemann body revealed induced cell proliferation in response to both LPS and ConA while proliferation of pyloric caeca and circulating coelomocytes remained sparse. By using confocal microscopy it was observed that both the morphology and functional behaviour of cells released from explants of coelomic epithelium showed high similarity to those of circulating phagocytes. It was concluded that the increased coelomocyte numbers observed in response to LPS and ConA were reflected in an induced cell proliferation in coelomic epithelium, axial organ and Tiedemann body, which reinforces the idea that these organs are HPTs and the sources of coelomocyte renewal.

A member of the p38 mitogen-activated protein kinase family is responsible for transcriptional induction of Dopa decarboxylase in the epidermis of Drosophila melanogaster during the innate immune response

Drosophila innate immunity is controlled primarily by the activation of IMD (immune deficiency) or Toll signaling leading to the production of antimicrobial peptides (AMPs). IMD signaling also activates the JUN N-terminal kinase (JNK) cascade, which is responsible for immune induction of non-antimicrobial peptide immune gene transcription though the transcription factor AP-1. Transcription of the Dopa decarboxylase (Ddc) gene is induced in response to gram-negative and gram-positive septic injury, but not aseptic wounding. Transcription is induced throughout the epidermis and not specifically at the site of infection. Ddc transcripts are detectible within 2 h and remain high for several hours following infection with either gram-negative or gram-positive bacteria. Using Ddc-green fluorescent protein (GFP) reporter gene constructs, we show that a conserved consensus AP-1 binding site upstream of the Ddc transcription start site is required for induction. However, neither the Toll, IMD, nor JNK pathway is involved. Rather, Ddc transcription depends on a previously uncharacterized member of the p38 mitogen-activated protein kinase family, p38c. We propose that the involvement of DDC in a new pathway involved in Drosophila immunity increases the levels of dopamine, which is metabolized to produce reactive quinones that exert an antimicrobial effect on invading bacteria.

Molecular control of phenoloxidase-induced melanin synthesis in an insect

The melanization reaction induced by activated phenoloxidase in arthropods must be tightly controlled because of excessive formation of quinones and excessive systemic melanization damage to the hosts. However, the molecular mechanism by which phenoloxidase-induced melanin synthesis is regulated in vivo is largely unknown. It is known that the Spätzle-processing enzyme is a key enzyme in the production of cleaved Spätzle from pro-Spätzle in the Drosophila Toll pathway. Here, we provide biochemical evidence that the Tenebrio molitor Spätzle-processing enzyme converts both the 79-kDa Tenebrio prophenoloxidase and Tenebrio clip-domain SPH1 zymogen to an active melanization complex. This complex, consisting of the 76-kDa Tenebrio phenoloxidase and an active form of Tenebrio clip-domain SPH1, efficiently produces melanin on the surface of bacteria, and this activity has a strong bactericidal effect. Interestingly, we found the phenoloxidase-induced melanization reaction to be tightly regulated by Tenebrio prophenoloxidase, which functions as a competitive inhibitor of melanization complex formation. These results demonstrate that the Tenebrio Toll pathway and the melanization reaction share a common serine protease for the regulation of these two major innate immune responses.

Shrimp thioredoxin is a potent antioxidant protein

Thioredoxin (TRX) is a main component of the redox homeostasis machinery in the cell and it is required for ribonucleotide reductase function among others. In invertebrates, the redox balance is compromised during disease and changes in the physiological state and it is one of the components of the innate immune response. In this work, the shrimp (Litopenaeus vannamei) LvTRX cDNA was sequenced, cloned and over-expressed in bacteria to further characterize the function of the recombinant protein. LvTRX was able to reduce insulin disulfides and it was a better antioxidant compared to reduced glutathione and ascorbic acid, by means of the Trolox Equivalent Antioxidant Capacity (TEAC) assay. Interestingly, LvTRX contains aside of the canonical active site CXXC disulfide motif, one Cys (C73) residue in the interface of a putative dimer previously reported for human TRX. Using qRT-PCR, we found that shrimp LvTRX is mainly expressed in gills and pleopods; the variation of LvTRX mRNA upon hypoxia and re-oxygenation is not statistically significant. LvTRX stands as an important antioxidant that must be considered in future physiological and immune challenges studies.

Photorhabdus luminescens genes induced upon insect infection

BACKGROUND

Photorhabdus luminescens is a Gram-negative luminescent enterobacterium and a symbiote to soil nematodes belonging to the species Heterorhabditis bacteriophora. P.luminescens is simultaneously highly pathogenic to insects. This bacterium exhibits a complex life cycle, including one symbiotic stage characterized by colonization of the upper nematode gut, and a pathogenic stage, characterized by release from the nematode into the hemocoel of insect larvae, resulting in rapid insect death caused by bacterial toxins. P. luminescens appears to sense and adapt to the novel host environment upon changing hosts, which facilitates the production of factors involved in survival within the host, host-killing, and -exploitation.

RESULTS

A differential fluorescence induction (DFI) approach was applied to identify genes that are up-regulated in the bacterium after infection of the insect host Galleria mellonella. For this purpose, a P. luminescens promoter-trap library utilizing the mCherry fluorophore as a reporter was constructed, and approximately 13,000 clones were screened for fluorescence induction in the presence of a G. mellonella larvae homogenate. Since P. luminescens has a variety of regulators that potentially sense chemical molecules, like hormones, the screen for up-regulated genes or operons was performed in vitro, excluding physicochemical signals like oxygen, temperature or osmolarity as variables. Clones (18) were obtained exhibiting at least 2.5-fold induced fluorescence and regarded as specific responders to insect homogenate. In combination with a bioinformatics approach, sequence motifs were identified in these DNA-fragments that are similar to 29 different promoters within the P. luminescens genome. By cloning each of the predicted promoters upstream of the reporter gene, induction was verified for 27 promoters in vitro, and for 24 promoters in viable G. mellonella larvae. Among the validated promoters are some known to regulate the expression of toxin genes, including tccC1 (encoding an insecticidal toxin complex), and others encoding putative toxins. A comparably high number of metabolic genes or operons were observed to be induced upon infection; among these were eutABC, hutUH, and agaZSVCD, which encode proteins involved in ethanolamine, histidine and tagatose degradation, respectively. The results reflect rearrangements in metabolism and the use of other metabolites available from the insect. Furthermore, enhanced activity of promoters controlling the expression of genes encoding enzymes linked to antibiotic production and/or resistance was observed. Antibiotic production and resistance may influence competition with other bacteria, and thus might be important for a successful infection. Lastly, several genes of unknown function were identified that may represent novel pathogenicity factors.

CONCLUSION

We show that a DFI screen is useful for identifying genes or operons induced by chemical stimuli, such as diluted insect homogenate. A bioinformatics comparison of motifs similar to known promoters is a powerful tool for identifying regulated genes or operons. We conclude that signals for the regulation of those genes or operons induced in P. luminescens upon insect infection may represent a wide variety of compounds that make up the insect host. Our results provide insight into the complex response to the host that occurs in a bacterial pathogen, particularly reflecting the potential for metabolic shifts and other specific changes associated with virulence.

The antioxidants dimethylsulfoxide and dimethylthiourea affect the immediate adhesion responses of larval haemocytes from 3 lepidopteran insect species

Antioxidants, dimethylsulfoxide (DMSO) and dimethylthiourea (DMTU), at concentrations not affecting the viability of blood cells (haemocytes) from the larval stage of 3 lepidopteran insects - Galleria mellonella, Lymantria dispar, and Malacosoma disstria - differed in their influence on the innate binding of haemocytes to glass, bacteria to haemocytes, and on humoral responses to alien materials. In vitro DMSO had little effect, whereas DMTU substantially impaired the adhesion of the haemocyte types, the plasmatocytes and granular cells, to slides as well as the attachment of Bacillus subtilis to these haemocytes. Although both antioxidants increased lysozyme and phenoloxidase activities, there was no correlation of enzyme activity and haemocyte adhesion responses, possibly reflecting sequestered radicals. Nitric oxide and hydroxyl radicals offset the DMTU effect. In the absence of antioxidants, inactivate protein kinases A (PKA) and C (PKC) enhanced haemocyte aggregation. In general, DMSO, as opposed to DMTU, did not alter the effects of PKA and PKC activators and inhibitors on haemocyte aggregation or of PKC and PKA activities. High concentrations of DMSO and all levels of DMTU, although inhibiting PKA and PKC, inhibited haemocyte adhesion to slides. Comparable results occurred for DMTU-treated haemocytes incubated with B. subtilis. In vivo DMSO, unlike DMTU, did not impair plasmatocyte or granular cell responses to foreign materials, including bacterial removal from the haemolymph and nodulation.