Molecular characterization of antimicrobial peptide genes of the carpenter ant Camponotus floridanus

Evolution of five environmentally responsive gene families in a pine-feeding sawfly, Neodiprion lecontei (Hymenoptera: Diprionidae)

A central goal in evolutionary biology is to determine the predictability of adaptive genetic changes. Despite many documented cases of convergent evolution at individual loci, little is known about the repeatability of gene family expansions and contractions. To address this void, we examined gene family evolution in the redheaded pine sawfly Neodiprion lecontei, a noneusocial hymenopteran and exemplar of a pine-specialized lineage evolved from angiosperm-feeding ancestors. After assembling and annotating a draft genome, we manually annotated multiple gene families with chemosensory, detoxification, or immunity functions before characterizing their genomic distributions and molecular evolution. We find evidence of recent expansions of bitter gustatory receptor, clan 3 cytochrome P450, olfactory receptor, and antimicrobial peptide subfamilies, with strong evidence of positive selection among paralogs in a clade of gustatory receptors possibly involved in the detection of bitter compounds. In contrast, these gene families had little evidence of recent contraction via pseudogenization. Overall, our results are consistent with the hypothesis that in response to novel selection pressures, gene families that mediate ecological interactions may expand and contract predictably. Testing this hypothesis will require the comparative analysis of high-quality annotation data from phylogenetically and ecologically diverse insect species and functionally diverse gene families. To this end, increasing sampling in under-sampled hymenopteran lineages and environmentally responsive gene families and standardizing manual annotation methods should be prioritized.

Unique antimicrobial activity in honey from the Australian honeypot ant (Camponotus inflatus)

Honey produced by the Australian honeypot ant (Camponotus inflatus) is valued nutritionally and medicinally by Indigenous peoples, but its antimicrobial activity has never been formally studied. Here, we determine the activity of honeypot ant honey (HPAH) against a panel of bacterial and fungal pathogens, investigate its chemical properties, and profile the bacterial and fungal microbiome of the honeypot ant for the first time. We found HPAH to have strong total activity against Staphylococcus aureus but not against other bacteria, and strong non-peroxide activity against Cryptococcus and Aspergillus sp. When compared with therapeutic-grade jarrah and manuka honey produced by honey bees, we found HPAH to have a markedly different antimicrobial activity and chemical properties, suggesting HPAH has a unique mode of antimicrobial action. We found the bacterial microbiome of honeypot ants to be dominated by the known endosymbiont genus Candidatus Blochmannia (99.75%), and the fungal microbiome to be dominated by the plant-associated genus Neocelosporium (92.77%). This study demonstrates that HPAH has unique antimicrobial characteristics that validate its therapeutic use by Indigenous peoples and may provide a lead for the discovery of novel antimicrobial compounds.

Assessing the effectiveness of AS-48 in experimental mice models of Chagas' disease

OBJECTIVES

We report the in vivo trypanocidal activity of the bacteriocin AS-48 (lacking toxicity), which is produced by Enterococcus faecalis, against the flagellated protozoan Trypanosoma cruzi, the aetiological agent of Chagas' disease.

METHODS

We determined the in vivo activity of AS-48 against the T. cruzi Arequipa strain in BALB/c mice (in both acute and chronic phases of Chagas' disease). We evaluated the parasitaemia, the reactivation of parasitaemia after immunosuppression and the nested parasites in the chronic phase by PCR in target tissues.

RESULTS

AS-48 reduced the parasitaemia profile in acute infection and showed a noteworthy reduction in the parasitic load in chronic infection after immunosuppression according to the results obtained by PCR (double-checking to demonstrate cure).

CONCLUSIONS

AS-48 is a promising alternative that provides a step forward in the development of a new therapy against Chagas' disease.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

Differential immune gene expression in sperm storage organs of leaf-cutting ants

Leaf-cutting ant queens mate with multiple males during a single nuptial flight and store sperm for up to two decades. During mating, males transfer sperm from their accessory testes to the queen bursa copulatrix from where it enters the spermatheca, an insect sperm storage organ that has become highly specialized in long-lived ant queens who never re-mate later in life. Long-term storage without the possibility to obtain new sperm creates an immune defence dilemma, because recognition of non-self cells eliminates infections but may also target irreplaceable sperm and reduce lifetime reproductive success. We therefore hypothesized that non-specific immune responses, like pathogen melanization, should be silenced in the spermatheca, because they rely on general non-self recognition, and that specific responses such as antimicrobial peptides are activated instead as they specifically target pathogenic bacteria and/or fungi. The maintenance of uninfected sperm cells by males before mating is not constrained by non-self recognition, meaning immune regulation might be more liberal in male reproductive organs. To test this hypothesis, we measured gene expression of two antimicrobial peptides, abaecin and defensin, and prophenoloxidase, an important enzyme of the melanization pathway, in male accessory glands and testes and in queen bursae copulatrix and spermathecae of Acromyrmex echinatior and Atta colombica leaf-cutting ants. As expected, prophenoloxidase expression was low in reproductive organs that sustain prolonged contact with sperm, whereas antimicrobial peptides showed average to high expression, indicating that leaf-cutting ants invest in specific rather than generalist immune defences for pathogen protection in organs that store sperm.

1,3,5-Triazino Peptide Derivatives: Synthesis, Characterization, and Preliminary Antileishmanial Activity

A library of short di-, tri-, and tetra-peptides with an s-triazine moiety at the N terminus and either an amide or ethyl ester C terminus was prepared in solution and on the solid phase. The two remaining positions of the s-triazine moiety were substituted with methoxy, morpholino, or piperidino groups. All the synthesized peptide derivatives were analyzed by HPLC and fully characterized by IR spectroscopy, ¹ H and ¹³ C NMR spectroscopy, elemental analysis, and mass spectrometry (MALDI TOF/TOF). A preliminary study of the antileishmanial activity of the 1,3,5-triazinyl peptide derivatives revealed that four dipeptide amide derivatives showed higher antipromastigote or antiamastigote activity than the reference standard drug miltefosine with no significance acute toxicity.

Diversity, evolution and medical applications of insect antimicrobial peptides

Antimicrobial peptides (AMPs) are short proteins with antimicrobial activity. A large portion of known AMPs originate from insects, and the number and diversity of these molecules in different species varies considerably. Insect AMPs represent a potential source of alternative antibiotics to address the limitation of current antibiotics, which has been caused by the emergence and spread of multidrug-resistant pathogens. To get more insight into AMPs, we investigated the diversity and evolution of insect AMPs by mapping their phylogenetic distribution, allowing us to predict the evolutionary origins of selected AMP families and to identify evolutionarily conserved and taxon-specific families. Furthermore, we highlight the use of the nematode Caenorhabditis elegans as a whole-animal model in high-throughput screening methods to identify AMPs with efficacy against human pathogens, including Acinetobacter baumanii and methicillin-resistant Staphylococcus aureus. We also discuss the potential medical applications of AMPs, including their use as alternatives for conventional antibiotics in ectopic therapies, their combined use with antibiotics to restore the susceptibility of multidrug-resistant pathogens, and their use as templates for the rational design of peptidomimetic drugs that overcome the disadvantages of therapeutic peptides.

The article is part of the themed issue ‘Evolutionary ecology of arthropod antimicrobial peptides’.

Scrutinizing the immune defence inventory of Camponotus floridanus applying total transcriptome sequencing

BACKGROUND

Defence mechanisms of organisms are shaped by their lifestyle, environment and pathogen pressure. Carpenter ants are social insects which live in huge colonies comprising genetically closely related individuals in high densities within nests. This lifestyle potentially facilitates the rapid spread of pathogens between individuals. In concert with their innate immune system, social insects may apply external immune defences to manipulate the microbial community among individuals and within nests. Additionally, carpenter ants carry a mutualistic intracellular and obligate endosymbiotic bacterium, possibly maintained and regulated by the innate immune system. Thus, different selective forces could shape internal immune defences of Camponotus floridanus.

RESULTS

The immune gene repertoire of C. floridanus was investigated by re-evaluating its genome sequence combined with a full transcriptome analysis of immune challenged and control animals using Illumina sequencing. The genome was re-annotated by mapping transcriptome reads and masking repeats. A total of 978 protein sequences were characterised further by annotating functional domains, leading to a change in their original annotation regarding function and domain composition in about 8% of all proteins. Based on homology analysis with key components of major immune pathways of insects, the C. floridanus immune-related genes were compared to those of Drosophila melanogaster, Apis mellifera, and other hymenoptera. This analysis revealed that overall the immune system of carpenter ants comprises many components found in these insects. In addition, several C. floridanus specific genes of yet unknown functions but which are strongly induced after immune challenge were discovered. In contrast to solitary insects like Drosophila or the hymenopteran Nasonia vitripennis, the number of genes encoding pattern recognition receptors specific for bacterial peptidoglycan (PGN) and a variety of known antimicrobial peptide (AMP) genes is lower in C. floridanus. The comparative analysis of gene expression post immune-challenge in different developmental stages of C. floridanus suggests a stronger induction of immune gene expression in larvae in comparison to adults.

CONCLUSIONS

The comparison of the immune system of C. floridanus with that of other insects revealed the presence of a broad immune repertoire. However, the relatively low number of PGN recognition proteins and AMPs, the identification of Camponotus specific putative immune genes, and stage specific differences in immune gene regulation reflects Camponotus specific evolution including adaptations to its lifestyle.

Identification and Characterization of a Novel Family of Cysteine-Rich Peptides (MgCRP-I) from Mytilus galloprovincialis

We report the identification of a novel gene family (named MgCRP-I) encoding short secreted cysteine-rich peptides in the Mediterranean mussel Mytilus galloprovincialis. These peptides display a highly conserved pre-pro region and a hypervariable mature peptide comprising six invariant cysteine residues arranged in three intramolecular disulfide bridges. Although their cysteine pattern is similar to cysteines-rich neurotoxic peptides of distantly related protostomes such as cone snails and arachnids, the different organization of the disulfide bridges observed in synthetic peptides and phylogenetic analyses revealed MgCRP-I as a novel protein family. Genome- and transcriptome-wide searches for orthologous sequences in other bivalve species indicated the unique presence of this gene family in Mytilus spp. Like many antimicrobial peptides and neurotoxins, MgCRP-I peptides are produced as pre-propeptides, usually have a net positive charge and likely derive from similar evolutionary mechanisms, that is, gene duplication and positive selection within the mature peptide region; however, synthetic MgCRP-I peptides did not display significant toxicity in cultured mammalian cells, insecticidal, antimicrobial, or antifungal activities. The functional role of MgCRP-I peptides in mussel physiology still remains puzzling.

Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions

BACKGROUND

The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions.

RESULTS

In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria.

CONCLUSIONS

This work provides evidence that while aphid's antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions.

Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions

Background

The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions.

Results

In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria.

Conclusions

This work provides evidence that while aphid’s antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-762) contains supplementary material, which is available to authorized users.

Antimicrobial peptides isolated from Phyllomedusa nordestina (Amphibia) alter the permeability of plasma membrane of Leishmania and Trypanosoma cruzi

Nature has provided inspiration for Drug Discovery studies and amphibian secretions have been used as a promising source of effective peptides which could be explored as novel drug prototypes for neglected parasitic diseases as Leishmaniasis and Chagas disease. In this study, we isolated four antimicrobial peptides (AMPs) from Phyllomedusa nordestina secretion, and studied their effectiveness against Leishmania (L.) infantum and Trypanosoma cruzi. The antiparasitic fractions were characterized by mass spectrometry and Edman degradation, leading to the identification of dermaseptins 1 and 4 and phylloseptins 7 and 8. T. cruzi trypomastigotes were susceptible to peptides, showing IC50 values in the range concentration of 0.25-0.68 μM. Leishmania (L.) infantum showed susceptibility to phylloseptin 7, presenting an IC50 value of 10 μM. Except for phylloseptin 7 which moderate showed cytotoxicity (IC50=34 μM), the peptides induced no cellular damage to mammalian cells. The lack of mitochondrial oxidative activity of parasites detected by the MTT assay, suggested that peptides were leishmanicidal and trypanocidal. By using the fluorescent probe SYTOX(®) Green, dermaseptins 1 and 4 and phylloseptins 7 and 8 showed time-dependent plasma membrane permeabilization of T. cruzi; phylloseptin 7 also showed a similar effect in Leishmania parasites. The present study demonstrates for the first time that AMPs target the plasma membrane of Leishmania and T. cruzi, leading to cellular death. Considering the potential of amphibian peptides against protozoan parasites and the reduced mammalian toxicity, they may contribute as scaffolds for drug design studies.

Ant genomics sheds light on the molecular regulation of social organization

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.

Gene expression analysis of the endosymbiont-bearing midgut tissue during ontogeny of the carpenter ant Camponotus floridanus

Insects have frequently evolved mutualistic relationships with extracellular and/or intracellular bacterial endosymbionts. Infection with endosymbionts seems to affect several cellular functions of the host such as immune pathways, oxidative stress regulation and autophagy. Our current knowledge about specific host factors leading to endosymbiont tolerance and/or control is still scarce and is based on very few associations between insect hosts and bacteria only. Camponotus floridanus ants harbour the obligate intracellular bacterium Blochmannia floridanus within specialized midgut cells called bacteriocytes. The number of Blochmannia endosymbionts within the midgut tissue increases strongly during host development and reaches a maximum at the late pupal stage, where the entire midgut is transformed into a symbiotic organ. After eclosion of workers the number of Blochmannia strongly decreases again. We chose 15 candidate genes from C. floridanus likely to be involved in host-symbiont interactions based on their significant homology to previously investigated symbiosis-relevant genes from other insects. We determined the expression of these genes in the endosymbiont-bearing midgut tissue in comparison to the residual body tissue at different developmental stages of C. floridanus in order to reveal changes in gene expression correlating with changes in endosymbiont number per host. Strikingly, two pattern recognition receptors (amidase PGRP-LB and PGRP-SC2) were highly expressed in the midgut tissue at the pupal stage, potentially down-modulating the IMD pathway to enable endosymbiont tolerance. Moreover, we investigated the immune gene expression in response to bacterial challenge at the pupal stage. Results showed that the midgut tissue differs in expression pattern in contrast to the residual body. Our results support a key role for amidase PGRPs, especially PGRP-LB, in regulation of the immune response towards endosymbionts in C. floridanus and suggest an involvement of the lysosomal system in control of Blochmannia endosymbionts.

In vivo antimicrobial evaluation of an alanine-rich peptide derived from Pleuronectes americanus

In several organisms, the first barrier against microbial infections consists of antimicrobial peptides (AMPs) which are molecules that act as components of the innate immune system. Recent studies have demonstrated that AMPs can perform various functions in different tissues or physiological conditions. In this view, this study was carried out in order to evaluate the multifunctional activity in vivo of an alanine-rich peptide, known as Pa-MAP, derived from the polar fish Pleuronectes americanus. Pa-MAP was evaluated in intraperitoneally infected mice with a sub-lethal concentration of Escherichia coli at standard concentrations of 1 and 5 mg kg(-1). At both concentrations, Pa-MAPs exhibited an ability to prevent E. coli infection and increase mice survival, similar to the result observed in mice treated with ampicillin at 2 mg kg(-1). In addition, mice were monitored for weight loss. The results showed that mice treated with Pa-MAPs at 1 mg kg(-1) gained 0.8% of body weight during the 72 h of experiment. The same was observed with Pa-MAP at 5 mg kg(-1), which had a gain of 0.5% in body weight during the treatment. Mice treated with ampicillin at 2 mg kg(-1) show a significant weight loss of 5.6% of body weight. The untreated group exhibited a 5.5% loss of body weight. The immunomodulatory effects were also evaluated by the quantification of IL-10, IL-12, TNF-α, IFN-γ and nitric oxide cytokines in serum, but no immunomodulatory activity was observed. Data presented here suggest that Pa-MAP should be used as a novel antibiotic against infection control.

Differential gene expression in Acromyrmex leaf-cutting ants after challenges with two fungal pathogens

Social insects in general and leaf-cutting ants in particular have increased selection pressures on their innate immune system due to their social lifestyle and monoclonality of the symbiotic fungal cultivar. As this symbiosis is obligate for both parties, prophylactic behavioural defences against infections are expected to increase either ant survival or fungus-garden survival, but also to possibly trade off when specific infections differ in potential danger. We examined the effectiveness of prophylactic behaviours and modulations of innate immune defences by a combination of inoculation bioassays and genome-wide transcriptomic studies (RNA-Seq), using an ant pathogen (Metarhizium brunneum) and a fungus-garden pathogen (Escovopsis weberi) and administering inoculations both directly and indirectly (via the symbiotic partner). Upon detection of pathogen conidia, ant workers responded by increasing both general activity and the frequency of specific defence behaviours (self-grooming, allo-grooming, garden-grooming) independent of the pathogen encountered. This trend was also evident in the patterns of gene expression change. Both direct and indirect (via fungus garden) inoculations with Metarhizium induced a general up-regulation of gene expression, including a number of well-known immune-related genes. In contrast, direct inoculation of the fungus garden by Escovopsis induced an overall down-regulation of ant gene expression, whereas indirect inoculation (via the ants) did not, suggesting that increased activity of ants to remove this fungus-garden pathogen is costly and involves trade-offs with the activation of other physiological pathways.