Isolation, cDNA cloning and gene expression of an antibacterial protein from larvae of the coconut rhinoceros beetle, Oryctes rhinoceros

A novel glycine-rich peptide from Zophobas atratus, coleoptericin B, targets bacterial membrane and protects against Klebsiella pneumoniae-induced mastitis in mice

OBJECTIVES

The growing occurrence of bacterial resistance has spawned the development of novel antimicrobial agents. Antimicrobial peptides, a class of small molecules with antimicrobial activity, have been regarded as the ideal alternatives to antibiotics.

METHODS

In this study, we amplified a new type of Zophobas atratus coleoptericin (denoted coleoptericin B) through rapid amplification of cDNA ends (RACE) PCR and expressed recombinant Z. atratus coleoptericin B (rZA-col B) by prokaryotic expression. Subsequently, we evaluated the antimicrobial effect and biocompatibility of rZA-col B in vivo, investigated its antimicrobial mechanism, and assessed its therapeutic effect in a murine model of mastitis caused by MDR Klebsiella pneumoniae.

RESULTS

The in vivo studies demonstrated that rZA-col B possesses broad-spectrum antimicrobial activity against both Gram-positive and Gram-negative bacteria. It exhibited less than 1.5% haemolysis and 10% cytotoxicity, even at a concentration of 128 μM. Additionally, rZA-col B had a minimal risk of inducing drug resistance. Furthermore, rZA-col B could disrupt the integrity of bacterial membranes, induce membrane permeabilization and ultimately lead to bacterial death. Importantly, rZA-col B also alleviated mastitis caused by MDR K. pneumoniae in a murine model by enhancing bacterial clearance, reducing neutrophil infiltration, decreasing TNF-α and IL-1β expression, and protecting the mammary barrier.

CONCLUSIONS

rZA-col B may be a promising antibacterial agent to combat MDR bacterial infection.

Diverse Host Immune Responses of Different Geographical Populations of the Coconut Rhinoceros Beetle to Oryctes Rhinoceros Nudivirus (OrNV) Infection

Incursions of the coconut rhinoceros beetle (CRB), Oryctes rhinoceros, into different islands in the South Pacific have been detected in recent years. It has been suggested that this range expansion is related to an O. rhinoceros haplotype reported to show reduced susceptibility to the well-established classical biocontrol agent, Oryctes rhinoceros nudivirus (OrNV). Our understanding of the genetic characteristics which distinguish the population of O. rhinoceros that has recently established in Solomon Islands from other well-established populations across the region is very limited. Here, we hypothesized that the recently established O. rhinoceros population should have greater innate immune responses when challenged by OrNV than those of well-established and native O. rhinoceros populations. We used the RNA sequencing (RNA-Seq) approach to generate gene expression profiles of midgut tissue from OrNV-infected and noninfected individuals collected in the Solomon Islands (recent incursion), Papua New Guinea and Fiji (previously established), and the Philippines (within the native range). The collections included individuals from each of the three major mitochondrial lineages (CRB-G, CRB-PNG, and CRB-S) known to the region, allowing us to explore the specific responses of each haplotype to infection. Although insects from the Philippines and Solomon Islands that were tested belong to the same mitochondrial lineage (CRB-G), their overall responses to infection were different. The number of differentially expressed genes between OrNV-infected and noninfected wild-caught individuals from the four different locations varied from 148 to 252. Persistent OrNV infection caused a high level of induced antimicrobial activity and immune responses in O. rhinoceros, but the direction and magnitude of the responses were population specific. The insects tested from the Solomon Islands displayed extremely high expression of genes which are known to be involved in immune responses (e.g. coleoptericin, cecropin, and serpin). These variations in the host immune system among insects from different geographical regions might be driven by variations in the virulence of OrNV isolates, and this requires further investigation. Overall, our current findings support the importance of immunity in insect pest incursion and an expansion of the pest's geographic range. IMPORTANCE Oryctes rhinoceros nudivirus (OrNV) is a double-stranded DNA (dsDNA) virus which has been used as a biocontrol agent to suppress coconut rhinoceros beetle (CRB) in the Pacific Islands. Recently a new wave of CRB incursions in Oceania is thought to be related to the presence of low-virulence isolates of OrNV or virus-tolerant haplotypes of beetles (CRB-G). Our comparative analysis of OrNV-infected and noninfected CRBs revealed that specific sets of genes were induced by viral infection in the beetles. This induction was much stronger in beetles collected from the Solomon Islands, a newly invaded country, than in individuals collected from within the beetle's native range (the Philippines) or from longer-established populations in its exotic range (Fiji and Papua New Guinea [PNG]). Beetles from the Philippines and the Solomon Islands that were tested in this study all belonged to the CRB-G haplotype, but the country-specific responses of the beetles to OrNV infection were different.

Culturing-Enriched Metabarcoding Analysis of the Oryctes rhinoceros Gut Microbiome

Simple Summary

The coconut rhinoceros beetle is a pest of palm trees, which may have symbiotic gut microbes that help it digest its food. These microbes may produce enzymes like cellulase, which have uses in human industry. If the microbes are essential for the beetle’s survival, then finding ways to attack the microbes could help fight the pest. We sampled microbes from the guts of larval beetles collected in coconut trees in southern Taiwan, and identified the microbes both by culturing and with molecular biology methods. We found several species of bacteria and a yeast, Candida xylanolytica, with potential digestive functions for the beetle. Some of these microbes had been reported in these beetles before while others are new. Broader surveys of the beetle microbiome are needed to determine whether or not they have a conserved microbiome.

Abstract

Wood-feeding insects should have a source of enzymes like cellulases to digest their food. These enzymes can be produced by the insect, or by microbes living in the wood and/or inside the insect gut. The coconut rhinoceros beetle, Oryctes rhinoceros, is a pest whose digestive microbes are of considerable interest. This study describes the compartments of the O. rhinoceros gut and compares their microbiomes using culturing-enriched metabarcoding. Beetle larvae were collected from a coconut grove in southern Taiwan. Gut contents from the midgut and hindgut were plated on nutrient agar and selective carboxymethylcellulose agar plates. DNA was extracted from gut and fat body samples and 16S rDNA metabarcoding performed to identify unculturable bacteria. Cellulase activity tests were performed on gut fluids and microbe isolates. The midgut and hindgut both showed cellulolytic activity. Bacillus cereus, Citrobacter koseri, and the cellulolytic fungus Candida xylanilytica were cultured from both gut sections in most larvae. Metabarcoding did not find Bacillus cereus, and found that either Citrobacter koseri or Paracoccus sp. were the dominant gut microbes in any given larva. No significant differences were found between midgut and hindgut microbiomes. Bacillus cereus and Citrobacter koseri are common animal gut microbes frequently found in Oryctes rhinoceros studies while Candida xylanilytica and the uncultured Paracoccus sp. had not been identified in this insect before. Some or all of these may well have digestive functions for the beetle, and are most likely acquired from the diet, meaning they may be transient commensalists rather than obligate mutualists. Broader collection efforts and tests with antibiotics will resolve ambiguities in the beetle–microbe interactions.

Transcriptome and microbiome of coconut rhinoceros beetle (Oryctes rhinoceros) larvae

BACKGROUND

The coconut rhinoceros beetle, Oryctes rhinoceros, is a major pest of palm crops in tropical Asia and the Pacific Islands. Little molecular data exists for this pest, impeding our ability to develop effective countermeasures and deal with the species' growing resistance to viral biocontrols. We present the first molecular biology analyses of this species, including a metagenomic assay to understand the microbiome of different sections of its digestive tract, and a transcriptomics assay to complement the microbiome data and to shed light on genes of interest like plant cell wall degrading enzymes and immunity and xenobiotic resistance genes.

RESULTS

The gut microbiota of Oryctes rhinoceros larvae is quite similar to that of the termite gut, as both species feed on decaying wood. We found the first evidence for endogenous beta-1,4-endoglucanase in the beetle, plus evidence for microbial cellobiase, suggesting the beetle can degrade cellulose together with its gut microfauna. A number of antimicrobial peptides are expressed, particularly by the fat body but also by the midgut and hindgut.

CONCLUSIONS

This transcriptome provides a wealth of data about the species' defense against chemical and biological threats, has uncovered several potentially new species of microbial symbionts, and significantly expands our knowledge about this pest.

A well protected intruder: the effective antimicrobial defense of the invasive ladybird Harmonia axyridis

The harlequin ladybird Harmonia axyridis (Coleoptera: Coccinellidae) is a polyphagous predatory beetle native to Central and Eastern Asia. Since 2007 it has established all over Central Europe. In order to elucidate which defense strategy is responsible for its high resistance to diseases, we tested hemolymph as well as eleven main components of the headspace of H. axyridis for antimicrobial activity against Gram-positive (Bacillus subtilis, B. thuringiensis ssp. tenebrionis, Micrococcus luteus) and Gram-negative bacteria (Escherichia coli) and yeast (Saccharomyces cerevisiae). While three of the volatile compounds weakly reduced the growth of microorganisms, hemolymph of adults and larvae of H. axyridis strongly inhibited the growth of Gram-positive and Gram-negative bacteria as well as yeast. Furthermore, we compared the antimicrobial activity in the hemolymph of H. axyridis and Coccinella septempunctata. Antimicrobial activity in H. axyridis was about a thousand times higher compared to hemolymph from C. septempunctata. In contrast to C. septempunctata, the antimicrobial activity in H. axyridis was present without prior challenge. Minimal inhibitory concentration (MIC) of the hemolymph of H. axyridis was lowest against E. coli and yeast followed by B. subtilis, and was highest against entomopathogenic B. thuringiensis ssp. tenebrionidae. Furthermore, MIC values of the hemolymph obtained from live beetles were significantly lower than from frozen insects. This suggests that the active antimicrobial compound is affected by freezing and subsequent thawing of the beetles. Potential implications of our findings for the competitive advantages of H. axyridis over C. septempunctata are discussed.

Isolation, cDNA cloning, and structure-based functional characterization of oryctin, a hemolymph protein from the coconut rhinoceros beetle, Oryctes rhinoceros, as a novel serine protease inhibitor

We isolated oryctin, a 66-residue peptide, from the hemolymph of the coconut rhinoceros beetle Oryctes rhinoceros and cloned its cDNA. Oryctin is dissimilar to any other known peptides in amino acid sequence, and its function has been unknown. To reveal that function, we determined the solution structure of recombinant (13)C,(15)N-labeled oryctin by heteronuclear NMR spectroscopy. Oryctin exhibits a fold similar to that of Kazal-type serine protease inhibitors but has a unique additional C-terminal α-helix. We performed protease inhibition assays of oryctin against several bacterial and eukaryotic proteases. Oryctin does inhibit the following serine proteases: α-chymotrypsin, endopeptidase K, subtilisin Carlsberg, and leukocyte elastase, with K(i) values of 3.9 × 10(-10) m, 6.2 × 10(-10) m, 1.4 × 10(-9) m, and 1.2 × 10(-8) m, respectively. Although the target molecule of oryctin in the beetle hemolymph remains obscure, our results showed that oryctin is a novel single domain Kazal-type inhibitor and could play a key role in protecting against bacterial infections.

Multipeptide precursor structure of acaloleptin A isoforms, antibacterial peptides from the Udo longicorn beetle, Acalolepta luxuriosa

We previously purified acaloleptin A1, A2, and A3, antibacterial peptides that are produced in the larval hemolymph of Acalolepta luxuriosa (Udo longicorn beetle). In this study, we performed cDNA cloning. The cDNA sequence showed a predicted acaloleptin A precursor that consisted of five acaloleptin A isoforms. Four (isoforms 1, 2, 3 and 4) of the five isoforms of the acaloleptin A precursor had high-level sequence identities with each other, but the N-terminal region of isoform 5 differed from those of the other acaloleptin A isoforms. Northern and Western blot analyses showed that acaloleptin A isoforms were mass-produced soon after bacterial inoculation. Finally, we purified isoform 5 from hemolymph of the immunized larvae. Isoform 5, unlike acaloleptin A1, A2 and A3, showed antimicrobial activities against a Gram-positive bacterium, Micrococcus luteus and a fungus, Magnaporthe grisea. These results suggest that the multipeptide structure of the acaloleptin A precursor allows A. luxuriosa high-level production of antibacterial peptides and resistance to a wide range of microorganisms.

Bactrocerin-1: a novel inducible antimicrobial peptide from pupae of oriental fruit fly Bactrocera dorsalis Hendel

A novel antimicrobial peptide, Bactrocerin-1, was purified and characterized from an immunized dipteran insect, Bactrocera dorsalis. Bactrocerin-1 has 20 amino acid residues with a mass of 2,325.95 Da. The amino acid sequence of Bactrocerin-1 showed very high similarity to the active fragment (46V-65S-NH(2)) of Coleoptericin A. The composition of amino acid residues revealed that Bactrocerin-1 is a hydrophobic, positively charged, and Lys/Ile/Gly-rich peptide. Minimal growth inhibition concentration (MIC) measurements for synthesized Bactrocerin-1 showed a very broad spectrum of anti-microbial activity against Gram-positive bacteria, Gram-negative bacteria, and fungi. Bactrocerin-1 did not show hemolytic activity toward mouse red blood cells even at a concentration of 50 microM. Analysis of the Helical-wheel projection and the CD spectrum suggested that Bactrocerin-1 contains the amphipathic alpha-helix.

Purification and cDNA cloning of a cecropin from the longicorn beetle, Acalolepta luxuriosa

We have cloned and characterized a novel antibacterial peptide from the hemolymph of the coleopteran insect Acalolepta luxuriosa, of the superfamily Cerambyocidea. This peptide is active against Micrococcus luteus and Escherichia coli, and the amino acid sequence deduced by cloning of the cDNA identifies it as a coleopteran cecropin. Sequence comparisons and phylogenetic analyses performed using Clustal X suggest that this cecropin is evolutionarily intermediate between dipteran and lepidopteran cecropins. The results of MALDI-TOF mass spectrometry indicate that the mature form of this antibacterial peptide is 35 amino acid residues in length and has an amidated C-terminal isoleucine. This report is the first description of a cecropin from a coleopteran insect.

Purification and cDNA cloning of Luxuriosin, a novel antibacterial peptide with Kunitz domain from the Longicorn Beetle, Acalolepta luxuriosa

We have purified a novel antibacterial peptide from the hemolymph of the coleopteran insect Acalolepta luxuriosa, of the family Cerambyocidae, and named it luxuriosin. This peptide showed growth-inhibitory activity against Micrococcus luteus and germination- and/or growth-inhibitory activity against the conidia from rice blast fungus, Magnaporthe grisea. The amino acid sequence determined by cDNA cloning identified luxuriosin as a peptide of 88 amino acids with a theoretical molecular weight of 10,368.34, containing a Kunitz domain.

Identification of 1-lysophosphatidylethanolamine (C(16:1)) as an antimicrobial compound in the housefly, Musca domestica

We observed that a methanolic whole body extract of uninfected last instar larvae of the housefly, Musca domestica, displayed antifungal and antibacterial activity. We have further purified this extract to a single active fraction using reversed phase high performance liquid chromatography. The pure fraction inhibited growth of the Gram-positive bacteria Bacillus thuringiensis and the yeast Saccharomyces cerevisiae, but not the Gram-negative bacteria Escherichia coli. The active compound was determined to have a molecular mass of 451.2 Da. Further analysis by nuclear magnetic resonance identified the substance as mono-unsaturated 1-lysophosphatidylethanolamine (C(16:1)) (1-LPE). The structurally different and more common 2-LPE have been described as mediators of the antimicrobial activity of rimenophenazine antibiotic agents (Van Rensburg et al., 1992). Our results suggest that the isolated 1-LPE displays a higher activity in comparison, possibly based on structure-specific differences in activity.

Purification and cDNA cloning of a novel antibacterial peptide with a cysteine-stabilized alphabeta motif from the longicorn beetle, Acalolepta luxuriosa

An antibacterial peptide from the hemolymph of a coleopteran insect, Acalolepta luxuriosa, in the superfamily Cerambyocidea was characterized. The mature antibacterial peptide had 27 amino acid residues with a theoretical molecular weight of 3099.29 and it showed antibacterial activity against Escherichia coli and Micrococcus luteus. The deduced amino acid sequence of the peptide showed that it had a cysteine-stabilized alphabeta motif with a C...CXXXC...C...CXC consensus sequence, like insect defensins. However, the results of a multiple sequence alignment and phylogenetic analysis with CLUSTAL X indicated that this peptide is a novel peptide with a cysteine-stabilized alphabeta motif that is distant from insect defensins.

Purification, characterization and gene expression of a glycine and proline-rich antibacterial protein family from larvae of a beetle, Allomyrina dichotoma

Two structurally related antibacterial proteins were isolated from larvae of a beetle, Allomyrina dichotoma, immunized with Escherichia coli. The two proteins were designated A. dichotoma (A. d.) coleoptericin A and B. The mature portion of A. d. coleoptericins deduced from nucleotide sequences of the cDNAs consists of seventy-two amino acids without cysteine residues and is rich in glycine (11.1%) and proline (11.1%). Comparison of the amino acid sequences of the A. d. coleoptericins revealed that these antibacterial proteins have 94%, 75%, 50% and 43% similarity to rhinocerosin, holotricin 2, coleoptericin and acaloleptin A1. Recombinant A. d. coleoptericin A and B showed strong antibacterial activity against Staphylococcus aureus, methicillin resistant S. aureus (MRSA) and Bacillus subtilis. Recombinant A. d. coleoptericin A and B were shown to not form pores through bacterial membranes of E. coli, but to hamper cell division. Results of Northern blotting showed that A. d. coleoptericin genes are inducible by bacteria and are expressed strongly in the fat bodies and haemocytes, and weakly in the Malpighian tubules. Analysis of the evolutionary relationship of amino acid sequences among A. d. coleoptericins and other antibacterial proteins suggests that A. d. coleoptericins, rhinocerosin and holotricin 2 are closely related and form a gene family.

Purification, cDNA cloning and modification of a defensin from the coconut rhinoceros beetle, Oryctes rhinoceros

A novel member of the insect defensins, a family of antibacterial peptides, was purified from larvae of the coconut rhinoceros beetle, Oryctes rhinoceros, immunized with Escherichia coli. A full-size cDNA was cloned by combining reverse-transcription PCR (RT-PCR), and 5'- and 3'-rapid amplification of cDNA ends (RACE). Analysis of the O. rhinoceros defensin gene expression showed it to be expressed in the fat body and hemocyte, midgut and Malpighian tubules. O. rhinoceros defensin showed strong antibacterial activity against Staphylococcus aureus. A 9-mer peptide amidated at its C-terminus, AHCLAICRK-NH2 (Ala22-Lys30-NH2), was synthesized based on the deduced amino-acid sequence, assumed to be an active site sequence by analogy with the sequence of a defensin isolated from larvae of the beetle Allomyrina dichotoma. This peptide showed antibacterial activity against S. aureus, methicillin-resistant S. aureus, E. coli and Pseudomonas aeruginosa. We further modified this oligopeptide and synthesized five 9-mer peptides, ALRLAIRKR-NH2, ALLLAIRKR-NH2, AWLLAIRKR-NH2, ALYLAIRKR-NH2 and ALWLAIRKR-NH2. These oligopeptides showed strong antibacterial activity against Gram-negative and Gram-positive bacteria. The antibacterial effect of Ala22-Lys30-NH2 analogues was due to its interaction with bacterial membranes, judging from the leakage of liposome-entrapped glucose. These Ala22-Lys30-NH2 analogues did not show haemolytic activity and did not inhibit the growth of murine fibroblast cells or macrophages, except for AWLLAIRKR-NH2.