Novel antimicrobial peptides identified from an endoparasitic wasp cDNA library

Proteotranscriptomics reveals the secretory dynamics of teratocytes, regulators of parasitization by an endoparasitoid wasp

Parasitoid wasps have evolved sophisticated mechanisms of host regulation that establish a favorable environment for the development of immature parasitoids. While maternal venom and symbiotic virus-like particles are well-known mechanisms of host regulation, another less-studied mechanism is the secretion of host regulation factors by cells called teratocytes, extra-embryonic cells released during parasitoid larval eclosion. Consequently, identification and characterization of teratocyte secretory products has not been reported in detail for any parasitoid wasp. We aimed to analyze teratocyte secretory products released into hemolymph of the larval sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) by its biological control agent, the koinobiont endoparasitoid wasp Cotesia flavipes Cameron, 1891 (Hymenoptera: Braconidae). Teratocytes were released upon eclosion of parasitoid larvae four days after parasitization (DAP) and increased in number and size until six DAP. Total D. saccharalis hemocyte viability was reduced immediately after parasitization until DAP 2, while total hemocyte count was lower from the third DAP, and phenoloxidase and lysozyme activity were disrupted compared to non-parasitized controls. To examine the secretory products of teratocytes, we generated a teratocyte transcriptome and compared its in silico translated open reading frames to mass spectra obtained from hemolymph from parasitized and unparasitized hosts. This led to the identification of 57 polypeptides secreted by teratocytes, the abundance of which we tracked over 0-10 DAP. Abundant teratocyte products included proteins similar to bracovirus proteins and multiple disulfide-rich peptides. Most teratocyte products accumulated in hemolymph, reaching their highest concentrations immediately before parasitoid pupation. Our results provide insights into host regulation by teratocytes and reveal molecules that may be useful in biotechnology.

Identification and recombinant expression of an antimicrobial peptide (cecropin B-like) from soybean pest Anticarsia gemmatalis

ABSTRACT

BACKGROUND

Insects can be found in numerous diverse environments, being exposed to pathogenic organisms like fungi and bacteria. Once these pathogens cross insect physical barriers, the innate immune system operates through cellular and humoral responses. Antimicrobial peptides are small molecules produced by immune signaling cascades that develop an important and generalist role in insect defenses against a variety of microorganisms. In the present work, a cecropin B-like peptide (AgCecropB) sequence was identified in the velvetbean caterpillar Anticarsia gemmatalis and cloned in a bacterial plasmid vector for further heterologous expression and antimicrobial tests.

METHODS

AgCecropB sequence (without the signal peptide) was cloned in the plasmid vector pET-M30-MBP and expressed in the Escherichia coli BL21(DE3) expression host. Expression was induced with IPTG and a recombinant peptide was purified using two affinity chromatography steps with Histrap column. The purified peptide was submitted to high-resolution mass spectrometry (HRMS) and structural analyses. Antimicrobial tests were performed using gram-positive (Bacillus thuringiensis) and gram-negative (Burkholderia kururiensis and E. coli) bacteria.

RESULTS

AgCecropB was expressed in E. coli BL21 (DE3) at 28°C with IPTG 0.5 mM. The recombinant peptide was purified and enriched after purification steps. HRMS confirmed AgCrecropB molecular mass (4.6 kDa) and circular dichroism assay showed α-helix structure in the presence of SDS. AgCrecropB inhibited almost 50% of gram-positive B. thuringiensis bacteria growth.

CONCLUSIONS

The first cecropin B-like peptide was described in A. gemmatalis and a recombinant peptide was expressed using a bacterial platform. Data confirmed tertiary structure as predicted for the cecropin peptide family. AgCecropB was capable to inhibit B. thuringiensis growth in vitro.

Insights into the venom protein components of the egg parasitoid Anastatus japonicus (Hymenoptera: Eupelmidae)

BACKGROUND

Parasitoid venom is composed of a complex mixture of various active substances with different biological functions and is injected in the host during the parasitoid oviposition. Anastatus japonicus (Hymenoptera: Eupelmidae) is an egg parasite of Tessaratoma papillosa (Hemiptera: Tessaratomidae). Although the venom of this egg parasitoid plays an important role in the parasitic process, relatively little work has been done to address the mechanism.

RESULTS

In the present study, proteomic analysis was performed to identify the proteins that play an important role in the parasitic process of A. japonicus. A total of 2084 proteins were identified, including 81 putative venom proteins, most of which were identified as Hexamerin, Chitinase 2, Calreticulin, Heat shock protein 83-like, Serine protease, Arginine kinase, Phosphoserine aminotransferase and Actin protein. Together the before (Be) and after (Af) parasitization venom contains 1628 proteins, including 212 DEPs with 181 and 31 significantly up-regulated and down-regulated respectively. In addition, 10 differentially expressed proteins (DEPs) with fold change ≥8.71 were subjected to RT-qPCR to validate the proteomic data. The differential expression analysis revealed that nine proteins were specifically present in the pre-parasitic venom, whereas 26 proteins were specific to the post-parasitic treatments. Results of RT-qPCR analysis showed high expression of the selected DEPs which further validated our proteomics data.

CONCLUSION

These new proteomic data greatly enrich our current knowledge about key venom proteins associated with parasitic process in A. japonicus and contribute to better understanding of the parasitic mechanisms leading to the development of new biological control strategies. © 2020 Society of Chemical Industry.

Venomics of the ectoparasitoid wasp Bracon nigricans

BACKGROUND

Venom is one of the most important sources of regulation factors used by parasitic Hymenoptera to redirect host physiology in favour of the developing offspring. This has stimulated a number of studies, both at functional and "omics" level, which, however, are still quite limited for ectophagous parasitoids that permanently paralyze and suppress their victims (i.e., idiobiont parasitoids).

RESULTS

Here we present a combined transcriptomic and proteomic study of the venom of the generalist idiobiont wasp Bracon nigricans, an ectophagous larval parasitoid of different lepidopteran species, for which we recently described the host regulation strategy and the functional role of the venom in the induction of physiological changes in parasitized hosts. The experimental approach used led to the identification of the main components of B. nigricans venom involved in host regulation. Enzymes degrading lipids, proteins and carbohydrates are likely involved in the mobilization of storage nutrients from the fat body and may concurrently be responsible for the release of neurotoxic fatty acids inducing paralysis, and for the modulation of host immune responses.

CONCLUSION

The present work contributes to fill the gap of knowledge on venom composition in ectoparasitoid wasps, and, along with our previous physiological study on this species, provides the foundation on which to develop a functional model of host regulation, based both on physiological and molecular data. This paves the way towards a better understanding of parasitism evolution in the basal lineages of Hymenoptera and to the possible exploitation of venom as source of bioinsecticidal molecules.

Microbial Symbionts of Parasitoids

Parasitoids depend on other insects for the development of their offspring. Their eggs are laid in or on a host insect that is consumed during juvenile development. Parasitoids harbor a diversity of microbial symbionts including viruses, bacteria, and fungi. In contrast to symbionts of herbivorous and hematophagous insects, parasitoid symbionts do not provide nutrients. Instead, they are involved in parasitoid reproduction, suppression of host immune responses, and manipulation of the behavior of herbivorous hosts. Moreover, recent research has shown that parasitoid symbionts such as polydnaviruses may also influence plant-mediated interactions among members of plant-associated communities at different trophic levels, such as herbivores, parasitoids, and hyperparasitoids. This implies that these symbionts have a much more extended phenotype than previously thought. This review focuses on the effects of parasitoid symbionts on direct and indirect species interactions and the consequences for community ecology.

Alteration of the phagocytosis and antimicrobial defense of Octodonta nipae (Coleoptera: Chrysomelidae) pupae to Escherichia coli following parasitism by Tetrastichus brontispae (Hymenoptera: Eulophidae)

Although parasites and microbial pathogens are both detrimental to insects, little information is currently available on the mechanism involved in how parasitized hosts balance their immune responses to defend against microbial infections. We addressed this in the present study by comparing the immune response between unparasitized and parasitized pupae of the chrysomelid beetle, Octodonta nipae (Maulik), to Escherichia coli invasion. In an in vivo survival assay, a markedly reduced number of E. coli colony-forming units per microliter was detected in parasitized pupae at 12 and 24 h post-parasitism, together with decreased phagocytosis and enhanced bactericidal activity at 12 h post-parasitism. The effects that parasitism had on the mRNA expression level of selected antimicrobial peptides (AMPs) of O. nipae pupae showed that nearly all transcripts of AMPs examined were highly upregulated during the early and late parasitism stages except defensin 2B, whose mRNA expression level was downregulated at 24 h post-parasitism. Further elucidation on the main maternal fluids responsible for alteration of the primary immune response against E. coli showed that ovarian fluid increased phagocytosis at 48 h post-injection. These results indicated that the enhanced degradation of E. coli in parasitized pupae resulted mainly from the elevated bactericidal activity without observing the increased transcripts of target AMPs. This study contributes to a better understanding of the mechanisms involved in the immune responses of a parasitized host to bacterial infections.

First extensive characterization of the venom gland from an egg parasitoid: structure, transcriptome and functional role

The venom gland is a ubiquitous organ in Hymenoptera. In insect parasitoids, the venom gland has been shown to have multiple functions including regulation of host immune response, host paralysis, host castration and developmental alteration. However, the role played by the venom gland has been mainly studied in parasitoids developing in larval or pupal hosts while little is known for parasitoids developing in insect eggs. We conducted the first extensive characterization of the venom of the endoparasitoid Ooencyrtus telenomicida (Vassiliev), a species that develops in eggs of the stink bug Nezara viridula (L.). In particular we investigated the structure of the venom apparatus, its functional role and conducted a transcriptomic analysis of the venom gland. We found that injection of O. telenomicida venom induces: 1) a melanized-like process in N. viridula host eggs (host-parasitoid interaction), 2) impairment of the larval development of the competitor Trissolcus basalis (Wollaston) (parasitoid-parasitoid interaction). The O. telenomicida venom gland transcriptome reveals a majority of digestive enzymes (peptidases and glycosylases) and oxidoreductases (laccases) among the most expressed genes. The former enzymes are likely to be involved in degradation of the host resources for the specific benefit of the O. telenomicida offspring. In turn, alteration of host resources caused by these enzymes may negatively affect the larval development of the competitor T. basalis. We hypothesize that the melanization process induced by venom injection could be related to the presence of laccases, which are multicopper oxidases that belong to the phenoloxidases group. This work contributed to a better understanding of the venom in insect parasitoids and allowed to identify candidate genes whose functional role can be investigated in future studies.

Anti-Inflammatory Activity of Crude Venom Isolated from Parasitoid Wasp, Bracon hebetor Say

Pest control in the agricultural fields, a major concern globally, is currently achieved through chemical or biological methods. Chemical methods, which leave toxic residue in the produce, are less preferred than biological methods. Venoms injected by stings of various wasps that kill the pest is considered as the examples of the biological method. Although several studies have investigated the biological control of pests through these venoms, very few studies have reported the effects of these venoms on mammalian cells. Bracon hebetor, an ectoparasitoid of the order Hymenoptera, is having a paramount importance in parasitizing various lepidopterous larvae including Plodia interpunctella also called as Indianmeal moth (IMM). Since it is biologically controlled by B. hebetor venom, therefore in our study, herein for the first time, we report the anti-inflammatory activities of the venom from B. hebetor (BHV). We developed a septic shock mice model for in vivo anti-inflammatory studies and RAW 264.7 cells for in vitro studies. Our results clearly demonstrate that BHV can dose dependently abrogate the nitric oxide (NO) production and suppress the levels of proinflammatory mediators and cytokines without posing any cytotoxicity via the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways.

Characterization and functional study of a Cecropin-like peptide from the Chinese oak silkworm, Antheraea pernyi

In present study, a Cecropin-like peptide from Antheraea pernyi (ApCec) was cloned and characterized. The full-length ApCec cDNA encoded a protein with 64 amino acids including a putative 22-amino-acid signal peptide, a 4-amino-acid propeptide, and a 38-amino-acid mature peptide. ApCec gene was highly expressed in Malpighian tubules of A. pernyi after induction for 24 h by Escherichia coli in PBS. Pro-ApCec (including propeptide and mature peptide) and M-ApCec (just mature peptide) were synthesized chemically and analyzed by HPLC and mass spectroscopy. The antibacterial activity of M-ApCec is more potent than pro-ApCec against E. coli K12 or B. subtilus in both minimum inhibitory concentration and inhibition zone assays. Hemolytic assay results showed M-ApCec possessed a low cytotoxicity to mammalian cells. The secondary structure of M-ApCec forms α-helical structure, shown by circular dichroism spectroscopy. Transmission electron microscopy analysis suggested that M-ApCec killed bacteria by disrupting bacterial cell membrane integrity. Our results indicate ApCec may play an important role in defending from pathogenic bacteria in A. pernyi, and it may be as a potential candidate for applications in antibacterial drug development and agriculture.

Venom Proteins from Parasitoid Wasps and Their Biological Functions

Parasitoid wasps are valuable biological control agents that suppress their host populations. Factors introduced by the female wasp at parasitization play significant roles in facilitating successful development of the parasitoid larva either inside (endoparasitoid) or outside (ectoparasitoid) the host. Wasp venoms consist of a complex cocktail of proteinacious and non-proteinacious components that may offer agrichemicals as well as pharmaceutical components to improve pest management or health related disorders. Undesirably, the constituents of only a small number of wasp venoms are known. In this article, we review the latest research on venom from parasitoid wasps with an emphasis on their biological function, applications and new approaches used in venom studies.

Structure-activity relationship of potent antimicrobial peptide analogs of Ixosin-B amide

There is a great urgency in developing a new generation of antibiotics and antimicrobial agents since the bacterial resistance to antibiotics have increased dramatically. A series of overlapped peptide fragments of Ixosin-B, an antimicrobial peptide with amino acid sequence of QLKVDLWGTRSGIQPEQHSSGKSDVRRWRSRY, was designed, synthesized and examined for their antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. A potent 11-mer peptide TSG-8-1, WWSYVRRWRSR-amide, was developed, which exhibited antimicrobial activity against E. coli and S. aureus while very little hemolytic activity in human erythrocytes was observed at high dose level. This peptide could be further modified for the development of a potent antimicrobial agent in the future.

Recyclable and stable silver deposited magnetic nanoparticles with poly (vinyl pyrrolidone)-catechol coated iron oxide for antimicrobial activity

This paper introduces a facile method to make highly stable and recyclable antimicrobial magnetic nanoparticles (NPs). Initially, magnetic iron oxide nanoparticles (IONPs) were coated with poly (vinyl pyrrolidone) conjugated catechol (PVP-CCDP). Afterward, silver nanoparticles (Ag(0)) were deposited onto PVP-CCDP coated IONPs using remain catechol. The prepared nanoparticles showed long term (~4 weeks) colloidal stability and redispersibility, respectively, against external magnetic field and over a broad range of pH (4-12). The NPs were characterized by UV-vis, SEM, XPS, and XRD measurements. TEM and DLS analyses showed that the mean particle size of PVP-CCDP coated IONPs/Ag(0) were about 72 nm. The recyclable magnetic NPs possessed a high antibacterial effect against the model microbes Staphylococcus aureus and Escherichia coli and could be separated easily using magnet following antibacterial test for repeated uses and maintained 100% antibacterial efficiency during three cycles. In MTT assay, the magnetic nanoparticles possessed no measureable cytotoxicity to live cells.

"It stings a bit but it cleans well": venoms of Hymenoptera and their antimicrobial potential

Venoms from Hymenoptera display a wide range of functions and biological roles. These notably include manipulation of the host, capture of prey and defense against competitors and predators thanks to endocrine and immune systems disruptors, neurotoxic, cytolytic and pain-inducing venom components. Recent works indicate that many hymenopteran species, whatever their life style, have also evolved a venom with properties which enable it to regulate microbial infections, both in stinging and stung animals. In contrast to biting insects and their salivary glands, stinging Hymenoptera seem to constitute an under-exploited ecological niche for agents of vector-borne disease. Few parasitic or mutualistic microorganisms have been reported to be hosted by venom-producing organs or to be transmitted to stung animals. This may result from the presence of potent antimicrobial molecules in venoms, histological features of venom apparatuses and selective effects of venoms on immune defenses of targeted organisms. The present paper reviews for the first time the venom antimicrobial potential of solitary and social Hymenoptera in molecular, ecological, and evolutionary perspectives.

Discovery of potent antimicrobial peptide analogs of Ixosin-B

Antimicrobial peptides (AMPs) represent the first defense line against infection when organisms are infected by pathogens. These peptides are generally good targets for the development of antimicrobial agents. Peptide amide analogs of Ixosin-B, an antimicrobial peptide with amino acid sequence of QLKVDLWGTRSGIQPEQHSSGKSDVRRWRSRY, were designed, synthesized and examined for antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Within the peptides synthesized, we discovered an 11-mer peptide, KRLRRVWRRWR-amide, which exhibited potent antimicrobial activity while very little hemolytic activity in human erythrocytes was observed even at high dose level (100 μM). With further modifications, this peptide could be developed into a potent antimicrobial agent in the future.

Modifying Fe3O4-functionalized nanoparticles with N-halamine and their magnetic/antibacterial properties

Magnetic/antibacterial bifunctional nanoparticles were fabricated through the immobilization of antibacterial N-halamine on silica-coated Fe(3)O(4)-decorated poly(styrene-co-acrylate acid) (PSA) nanoparticles. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The N-halamine was developed from the precursor 5,5-dimethylhydantoin (DMH) by chlorination treatment, and experimental results showed that the loading amount of DMH on the silica-coated Fe(3)O(4)-decorated poly(styrene-co-acrylate acid) nanoparticles was adjustable. The as-synthesized nanoparticles exhibited superparamagnetic behavior and had a saturation magnetization of 18.93 emu g(-1). Antibacterial tests showed that the resultant nanoparticles displayed enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria compared with their bulk counterparts.

Characterization of an abaecin-like antimicrobial peptide identified from a Pteromalus puparum cDNA clone

Abaecin is a major antimicrobial peptide, initially identified from the honeybee. In our effort to discover new antimicrobial peptides from the endoparasitoid wasp Pteromalus puparum, we identified an antibacterial cDNA clone that codes a fragment with high amino acid sequence similarity to abaecin. The proline-rich peptide (YVPPVQKPHPNGPKFPTFP, named PP30) was chemically synthesized and characterized in this study. Antimicrobial assays indicated that the cationic peptide was active against both Gram-negative and positive bacteria, but not active against fungi tested. No hemolytic activity was observed against human erythrocytes after 1h incubation at concentration of 125 microM or below. The antibacterial activity of PP30 against Escherichia coli was attenuated in the presence of increasing concentrations of NaCl. Transmission electron microscopic (TEM) examination of PP30-treated E. coli cells showed morphological changes in the cells and extensive damage to the cell membranes. The circular dichroism (CD) spectroscopy studies indicated that PP30 formed random coil structures in phosphate buffer (pH 7.4), 50% TFE and 25 mM SDS solution. Expression analysis of the gene coding for the peptide indicated that its expression was upregulated upon bacterial infection, indicating that the gene may play a role in preventing potential infection by microorganisms during parasitization in Pieris rapae.