cDNA cloning and molecular characterization of a defensin-like antimicrobial peptide from larvae of Protaetia brevitarsis seulensis (Kolbe)

Inhibition of Zoonotic Pathogens Naturally Found in Pig Manure by Black Soldier Fly Larvae and Their Intestine Bacteria

Simple Summary

With the rapid development of the economy and the improvement of people’s living standards, people need to rear a lot of livestock to meet demand for proteins. This also involves an increase in the production of livestock manure. The expanding rate of livestock manure has become a thorny issue, owing to characteristics such as plentiful nitrogen and abundant zoonotic pathogens. The saprophagous larvae of the black soldier fly (BSF) are often associated with animal manure and can significantly reduce the populations of different zoonotic pathogens in livestock manure. However, reports about the mechanisms of this phenomenon are scarce. In this study, we investigated the potential mechanisms of BSF larvae in reducing the zoonotic pathogens naturally found in pig manure. The results clearly showed that zoonotic pathogens in pig manure were significantly decreased after being treated with BSF larvae, and also suggested that the antimicrobial peptides produced by the BSF larvae and gut-associated bacteria are able to antagonize the zoonotic pathogens. This study will contribute to reveal the potential antagonistic mechanisms of BSF larvae against zoonotic pathogens and improve the safety of organic waste conversion by BSF larvae.

Abstract

Black soldier fly (BSF) larvae are often exposed to organic waste which harbors abundant zoonotic pathogens. We investigated the ability of BSF larvae to inhibit the zoonotic pathogens naturally found in pig manure. The zoonotic pathogens populations were detected by using selective medium during the conversion. Results showed that the viability of the zoonotic pathogens in pig manure was significantly affected. After eight days of conversion, the Coliform populations were undetected, and Staphylococcus aureus and Salmonella spp. decreased significantly on the eighth day. Antimicrobial assays of the purified recombinant defensin-like peptide 4 (DLP4) showed that this peptide exhibits inhibitory activity against S. aureus, Salmonella enterica serovar typhimurium, and Escherichia coli in vitro. Bacteria BSF-CL and BSF-F were isolated from the larvae gut, and both inhibited the growth of S. aureus and E. coli, but Salmonella spp. was sensitive to the BSF-CL strain (but not to the BSF-F strain). The results from our experiments indicate that BSF larvae are capable of functionally inhibiting potential zoonotic pathogens in pig manure through a variety of mechanisms including antimicrobial peptides expression and the gut associate microorganisms. This study provides a theoretical basis for further study on the combined mechanism of BSF larvae immunity and its gut microbes against the zoonotic pathogens in pig manure.

Structural and functional characterizations and heterogenous expression of the antimicrobial peptides, Hidefensins, from black soldier fly, Hermetia illucens (L.)

Insect defensins are effector components of the innate defense system. Defensins, which are widely distributed among insects, are a type of small cysteine-rich plant antimicrobial peptides with broad-spectrum antimicrobial activity. Here, the cDNAs of the black soldier fly, Hermetia illucens (L.), encoding six defensins, designated herein as Hidefensin1-1, 2, 3, 4, 5, 6. Moreover, Hidefensin1-1, 2, and 5 were identified for the first time by genome-targeted analysis. These Hidefensins were found to mainly adopt α-helix and β-sheet conformation homology as modeled by PRABI, Swiss-Model and ProFunc server. Six conserved cysteine residues that contribute to three disulfide bonds formed the spacing pattern "C-X₁₂-C-X₃-C-X₉-C-X₅-C-X-C", which play a vital role in the molecular stability of Hidefensins. Phylogenetic analysis revealed that the homology of five Hidefensins (except Hidefensin4) was about 59%-92% compared with other insect defensins, indicating that they are novel antimicrobial peptides genes in black soldier fly. Furthermore, the Hidefensin1-1 was expressed in the Escherichia coli strain BL21(DE3) as a fusion protein with thioredoxin. Results showed that the purified TRX-Hidefensin1-1 exerted strong inhibitory effects against the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. The inhibitory efficacy of TRX-Hidefensin1-1 against Gram-positive bacteria was better than that against Gram-negative bacteria. These results indicated that Hidefensin1-1 has potent antimicrobial activities against test pathogens.

LJ, Franco Castrillón J, Rojas-Montoya M, Castaño Osorio JC. New Insect Host Defense Peptides (HDP) From Dung Beetle (Coleoptera: Scarabaeidae) Transcriptomes

The Coleoptera Scarabaeidae family is one of the most diverse groups of insects on the planet, which live in complex microbiological environments. Their immune systems have evolved diverse families of Host Defense Peptides (HDP) with strong antimicrobial and immunomodulatory activities. However, there are several peptide sequences that await discovery in this group of organisms. This would pave the way to identify molecules with promising therapeutic potential. This work retrieved two sources of information: 1) De-novo transcriptomic data from two species of neotropical Scarabaeidae (Dichotomius satanas and Ontophagus curvicornis); 2) Sequence data deposited in available databases. A Blast-based search was conducted against the transcriptomes with a subset of sequences representative of the HDP. This work reports 155 novel HDP sequences identified in nine transcriptomes from seven species of Coleoptera: D. satanas (n = 76; 49.03%), O. curvicornis (n = 23; 14.83%), (Trypoxylus dichotomus) (n = 18; 11.61%), (Onthophagus nigriventris) (n = 10; 6.45%), (Heterochelus sp) (n = 6; 3.87%), (Oxysternon conspicillatum) (n = 18; 11.61%), and (Popillia japonica) (n = 4; 2.58%). These sequences were identified based on similarity to known HDP insect families. New members of defensins (n = 58; 37.42%), cecropins (n = 18; 11.61%), attancins (n = 41; 26.45%), and coleoptericins (n = 38; 24.52%) were described based on their physicochemical and structural characteristics, as well as their sequence relationship to other insect HDPs. Therefore, the Scarabaeidae family is a complex and rich group of insects with a great diversity of antimicrobial peptides with potential antimicrobial activity.

De novo genome assembly of the white-spotted flower chafer (Protaetia brevitarsis)

BACKGROUND

Protaetia brevitarsis, commonly known as the white-spotted flower chafer, is an important Scarabaeidae insect that is distributed in most Asian countries. Recently, research on the insect's harmfulness to crops, usefulness in agricultural waste utilization, edibility, medicinal value, and usability in insect immunology has provided sufficient impetus to demonstrate the need for a detailed study of its biology. Herein, we sequenced the whole genome of this species to improve our understanding and study of P. brevitarsis.

FINDINGS

We developed a highly reliable genome resource for P. brevitarsis (Lewis, 1879; Coleoptera: Cetoniinae) using Illumina and PacBio sequencing platforms. A total of 135.75 gigabases (Gb) was generated, providing 150-fold coverage based on the 810-megabases (Mb) estimated genome size. The assembled P. brevitarsis genome was 751 Mb (including the scaffolds longer than 2 kilobases (kb)) with 327 scaffolds, and the N50 length of the assembly was 2.94 Mb. A total of 34,110 (22,229 in scaffolds and 11,881 located in alleles) genes were identified using Evidence Modeler, which was based on the gene prediction results obtained from 3 different methods (ab initio, RNA sequencing based, and known gene based).

CONCLUSIONS

We assembled a high-quality P. brevitarsis genome, which will not only provide insight into the biology of the species but also provide a wealth of information that will inform researchers on the evolution, control, and utilization of P. brevitarsis.

Structure-Activity Relationships of Insect Defensins

Insects make up the largest and most diverse group of organisms on earth with several million species to exist in total. Considering the sheer number of insect species and the vast variety of ways they interact with their environment through chemistry, it is clear that they have significant potential as a source of new lead molecules. They have adapted to a range of ecological habitats and exhibit a symbiotic lifestyle with various microbes such as bacteria and fungi. Accordingly, numerous antimicrobial compounds have been identified including for example defensin peptides. Insect defensins were found to have broad-spectrum activity against various gram-positive/negative bacteria as well as fungi. They exhibit a unique structural topology involving the complex arrangement of three disulfide bonds as well as an alpha helix and beta sheets, which is known as cysteine-stabilized αβ motif. Their stability and amenability to peptide engineering make them promising candidates for the development of novel antibiotics lead molecules. This review highlights the current knowledge regarding the structure-activity relationships of insect defensin peptides and provides basis for future studies focusing on the rational design of novel cysteine-rich antimicrobial peptides.

Screening, Expression, Purification and Functional Characterization of Novel Antimicrobial Peptide Genes from Hermetia illucens (L.)

Antimicrobial peptides from a wide spectrum of insects possess potent microbicidal properties against microbial-related diseases. In this study, seven new gene fragments of three types of antimicrobial peptides were obtained from Hermetia illucens (L), and were named cecropinZ1, sarcotoxin1, sarcotoxin (2a), sarcotoxin (2b), sarcotoxin3, stomoxynZH1, and stomoxynZH1(a). Among these genes, a 189-basepair gene (stomoxynZH1) was cloned into the pET32a expression vector and expressed in the Escherichia coli as a fusion protein with thioredoxin. Results show that Trx-stomoxynZH1 exhibits diverse inhibitory activity on various pathogens, including Gram-positive bacterium Staphylococcus aureus, Gram-negative bacterium Escherichia coli, fungus Rhizoctonia solani Khün (rice)-10, and fungus Sclerotinia sclerotiorum (Lib.) de Bary-14. The minimum inhibitory concentration of Trx-stomoxynZH1 is higher against Gram-positive bacteria than against Gram-negative bacteria but similar between the fungal strains. These results indicate that H. illucens (L.) could provide a rich source for the discovery of novel antimicrobial peptides. Importantly, stomoxynZH1 displays a potential benefit in controlling antibiotic-resistant pathogens.