Entomopathogenic Bacteria Research Articles

In vitro evaluation of biocontrol potential of symbiotic bacteria of entomopathogenic nematodes against shoot and fruit borer (Helicoverpa armigera) in Solanaceous vegetable crops grown in seedling trays under greenhouse condition

The present study was carried out to test the biocontrol potential of symbiotic bacteria, Photorhabdus and Xenorhabdus against the shoot and fruit borer, Helicoverpa armigera in solanaceous vegetable crops grown under greenhouse conditions. A total of ten treatments were designed with symbiotic bacteria of entomopathogenic nematodes for testing their biocontrol potential by using Bacillus thuringiensis as a reference strain. The results had shown significantly higher biocontrol efficiency in the treatment T9 (H. armigera + Consortia) with 85-90% biocontrol efficiency in all the vegetable crops followed by the treatment T7 received Bacillus thuringiensis. Among the treatments received individual strains of entomopathogenic bacteria, T3 and T2 which received EPB3 and EPB1 with 75-80% biocontrol potential and are at par with each other. Other treatment received individual strains had shown more than 50% of biocontrol efficiency in vegetable crops grown in seedling trays under greenhouse conditions. Further these entomopathogenic bacteria can be tested for their effectivity under field trails and can be developed as bio-pesticide formulations either in the form of individual application or in integrated pest management for plant protection practices.

Insecticidal potential of Brevibacillus laterosporus against dipteran pest species in a wide ecological range

In order to increase our understanding of the insecticidal potential of the entomopathogenic bacterium Brevibacillus laterosporus strain UNISS 18 against insect pests, investigations were conducted on a selection of dipteran species including fruit flies, house flies, blow flies, and mosquitoes, characterized by adaptations to very diverse habitats.According to lethal concentration (LC50) values, the common house mosquito Culex pipiens (LC50 = 0.10 × 106 spores/mL) and the yellow fever mosquito Aedes aegypti (LC50 = 0.18 × 106 spores/mL) were significantly more susceptible than the flies. The blow flies were the second taxon in term of susceptibility to B. laterosporus spores, with a higher mortality in Calliphora vomitoria (LC50 = 78.84 × 106 spores/mL) than Lucilia caesar (LC50 = 148.30 × 106 spores/mL). The effectiveness of B. laterosporus spores was reduced by half in the house fly Musca domestica (LC50 = 82.41 × 106 spores/mL). The lowest susceptibility was observed in the fruit flies, among which the spotted wing drosophila (SWD), Drosophila suzukii, was the most susceptible (LC50 = 217.51 × 106 spores/mL) in comparison with the medfly Ceratitis capitata and the olive fly Bactrocera oleae (LC50 = 2567.32 and 2567.36 × 106 spores/mL, respectively). The present study demonstrated that significantly different degrees of susceptibility are associated with diverse dipteran species including plant and animal parasites, and we suggest that B. laterosporus established different relationships with dipteran species in different ecosystems.

Bacillus thuringiensis spp. israelensis and Control of Aedes aegypti Invasive Mosquitoes Species in Ecosystems

The review presents materials on microbiocontrol of vector mosquitoes using entomopathogenic bacteria Bacillus thuringiensis ssp. israelensis (Bti). Control of invasive ectoparasites is a major health issue, as mosquito species are capable of transmitting diseases, including extremely dangerous human and animal infections (malaria, tularemia, yellow fever, hemorrhagic fevers, dengue fever, taiga (or tickborne) encephalitis, filariasis, Ku fever, cattle anaplasmosis and many other infections and invasions). Bti is considered worldwide as a promising microbial agent that combines targeted efficacy in protective measures and environmental safety. The study of the effect of Bti δ-endotoxins on the intestinal epithelium of Aedes genus mosquitoes, search and characterization of specific receptors are extremely important for understanding the mechanism of action and activity of entomocidal proteins, the basis of the pathogenic effect of polytypic B. thuringiensis. Synergism, a combination of selective larvicidal action of natural Bti strains in combination with strategies of resistance emergence preventing demonstrate a wide range of possibilities of their use and unique evolutionary features of this endospore-forming bacterium as a modern larvicidal agent against Aedes aegypti population.

Transgenic expression of antimicrobial peptides from black soldier fly enhance resistance against entomopathogenic bacteria in the silkworm, Bombyx mori

Antimicrobial peptides (AMPs) are effective molecules produced by the innate immune system of most organisms to fend off invading microbes and regarded as promising alternatives to conventional antibiotics due to their potent antimicrobial activities. The larvae of black soldier fly (BSF), Hermetia illucens, inhabit microbe-rich environments and its insect genome encodes a broad repertoire of AMPs. In the present study, three AMPs encoded by BSF Hidefensin-1, Hidiptericin-1 and HiCG13551 were cloned, expressed and purified in a recombinant Escherichia coli expression system. In vitro, both Hidefensin-1 and Hidiptericin-1 inhibited the growth of Streptococcus pneumoniae and Escherichia coli, while HiCG13551 inhibited the growth of Staphylococcus aureus and E. coli. Transmission electron microscopy showed that Hidiptericin-1 inhibited bacterial growth through bacterial membrane lysis. We also constructed a transgenic silkworm line constitutively expressing an AMP cassette HiAMP4516 encoding all the three AMPs, and the silkworms showed an increased resistance to both gram-positive and gram-negative entomopathogenic bacteria. These results provide insights into the antibacterial activities of BSF AMPs both in vitro and in vivo and suggest a great potential of exploiting insect-derived AMPs in silkworm disease resistance breeding.

DISTRIBUCIÓN DE HONGOS ENTOMOPATÓGENOS EN SUELOS DE UNIDADES DE PRODUCCIÓN BOVINA Y FACTORES ASOCIADOS A SU PRESENCIA EN EL TRÓPICO MEXICANO

<strong>Background. </strong>Ticks are one of the main threats that affect cattle production in Mexico. In the ecosystems, these parasites are naturally regulated by microorganisms such as entomopathogenic fungi (EPF) and bacteria, wich are capable of causing them disease and death. However, some studies mention that the effects of climate change and wrong practices in the management of grasslands, trees and animals affect the distribution of these beneficial organisms in the livestock areas of Mexican tropic. <strong>Objectives.</strong> 1) To determine the distribution of EPF in cattle farm soils from the Mexican Tropics, 2) to identify the sites within the cattle farms with greatest presence and richness of EPF and 3) to identify factors associated with their presence. <strong>Methodology.</strong> Soil samples of seventy-two cattle farms from twelve municipalities of Veracruz, México, with high prevalence of ectoparasites, were collected. <em>Galleria mellonella</em> larvae were used as bait in order to isolate EPF from soils; then, fungi were identified by molecular methods. <strong>Results.</strong> Four genera of EPF were isolated and <em>M</em>. <em>anisopliae</em> was the most prevalent. Live fences soils showed the greatest EPF richness. The mountainous region (OR=2.25), cattle farm altitude (401-600 meters above sea level) (OR=3.81) and cattle farms where they do not use herbicides (OR=3.66) are factors associated to the presence of EPF in cattle farms soils (<em>P</em> < 0.05). <strong>Implications.</strong> Information about distribution and diversity of EPF, as well as the knowledge of factors that may affect them, will help to understand their importance as natural regulators of pests in cattle farms, to regulate agronomic activities to optimize their survival and help to design strategies for isolation of native EPF with potential bio-regulatory effects of ectoparasites. <strong>Conclusions.</strong> The isolation and richness of EPF in soils destined for the production of grazing cattle where <em>Metarhizium anisopliae</em> was the most isolated is reported for the first time in Mexico. The live fences soils presented the greatest wealth of EPF and some management and geographic characteristics were identified as factors associated with the fungal presence.

Infection\xa0of highly insecticide-resistant malaria vector Anopheles coluzzii with entomopathogenic bacteria Chromobacterium violaceum reduces its survival, blood feeding propensity and fecundity

BackgroundThis is now a concern that malaria eradication will not be achieved without the introduction of novel control tools. Microbiological control might be able to make a greater contribution to vector control in the future. The interactions between bacteria and mosquito make mosquito microbiota really promising from a disease control perspective. Here, the impact of Chromobacterium violaceum infections, isolated from both larvae and adult of wild-caught Anopheles gambiae sensu lato mosquitoes in Burkina Faso, was evaluated on mosquito survival, blood feeding and fecundity.MethodsTo assess entomopathogenic effects of C. violaceum infection on mosquitoes, three different types of bioassays were performed in laboratory. These bioassays aimed to evaluate the impact of C. violaceum infection on mosquito survival, blood feeding and fecundity, respectively. During bioassays mosquitoes were infected through the well-established system of cotton ball soaked with 6% glucose containing C. violaceum.ResultsChromobacterium violaceum kills pyrethroid resistant Anopheles coluzzii (LT80 of 8.78 days ± 0.18 at 108 bacteria cell/ml of sugar meal). Interestingly, this bacterium had other negative effects on mosquito lifespan by significantly reducing (~ 59%, P < 0.001) the mosquito feeding willingness from day 4-post infection (~ 81% would seek a host to blood feed) to 9- day post infection (22 ± 4.62% would seek a host to blood feed). Moreover, C. violaceum considerably jeopardized the egg laying (~ 16 eggs laid/mosquito with C. violaceum infected mosquitoes vs ~ 129 eggs laid/mosquito with control mosquitoes) and hatching of mosquitoes (a reduction of ~ 22% of hatching rate with C. violaceum infected mosquitoes). Compared to the bacterial uninfected mosquitoes, mosquitoes infected with C. violaceum showed significantly higher retention rates of immature eggs and follicles.ConclusionThese data showed important properties of Burkina Faso C. violaceum strains, which are highly virulent against insecticide-resistant An. coluzzii, and reduce both mosquito blood feeding and fecundity propensities. However, additional studies as the sequencing of C. violaceum genome and the potential toxins secreted will provide useful information render it a potential candidate for the biological control strategies of malaria and other disease vectors.

Temperature Restriction in Entomopathogenic Bacteria.

Temperature plays an important role in bacteria-host interactions and can be a determining factor for host switching. In this study we sought to investigate the reasons behind growth temperature restriction in the entomopathogenic enterobacterium Photorhabdus. Photorhabdus has a complex dual symbiotic and pathogenic life cycle. The genus consists of 19 species but only one subgroup, previously all classed together as Photorhabdus asymbiotica, have been shown to cause human disease. These clinical isolates necessarily need to be able to grow at 37°C, whilst the remaining species are largely restricted to growth temperatures below 34°C and are therefore unable to infect mammalian hosts. Here, we have isolated spontaneous mutant lines of Photorhabdus laumondii DJC that were able to grow up to 36–37°C. Following whole genome sequencing of 29 of these mutants we identified a single gene, encoding a protein with a RecG-like helicase domain that for the majority of isolates contained single nucleotide polymorphisms. Importantly, provision of the wild-type allele of this gene in trans restored the temperature restriction, confirming the mutations are recessive, and the dominant effect of the protein product of this gene. The gene appears to be part of a short three cistron operon, which we have termed the Temperature Restricting Locus (TRL). Transcription reporter strains revealed that this operon is induced upon the switch from 30 to 36°C, leading to replication arrest of the bacteria. TRL is absent from all of the human pathogenic species so far examined, although its presence is not uniform in different strains of the Photorhabdus luminescens subgroup. In a wider context, the presence of this gene is not limited to Photorhabdus, being found in phylogenetically diverse proteobacteria. We therefore suggest that this system may play a more fundamental role in temperature restriction in diverse species, relating to as yet cryptic aspects of their ecological niches and life cycle requirements.

Making 3D-Cry Toxin Mutants: Much More Than a Tool of Understanding Toxins Mechanism of Action.

3D-Cry toxins, produced by the entomopathogenic bacterium Bacillus thuringiensis, have been extensively mutated in order to elucidate their elegant and complex mechanism of action necessary to kill susceptible insects. Together with the study of the resistant insects, 3D-Cry toxin mutants represent one of the pillars to understanding how these toxins exert their activity on their host. The principle is simple, if an amino acid is involved and essential in the mechanism of action, when substituted, the activity of the toxin will be diminished. However, some of the constructed 3D-Cry toxin mutants have shown an enhanced activity against their target insects compared to the parental toxins, suggesting that it is possible to produce novel versions of the natural toxins with an improved performance in the laboratory. In this report, all mutants with an enhanced activity obtained by accident in mutagenesis studies, together with all the variants obtained by rational design or by directed mutagenesis, were compiled. A description of the improved mutants was made considering their historical context and the parallel development of the protein engineering techniques that have been used to obtain them. This report demonstrates that artificial 3D-Cry toxins made in laboratories are a real alternative to natural toxins.

Efficacy of Several Entomopathogenic Microorganism as Microbial Insecticide against Insect Pest on Chili (Capsicum annum L.)

The purpose of this study was to apply microbial suspension of which formulated as bio-insecticide to observe its effectiveness in controlling insect pest on chili plants, Capsicum annum L. The efficacy of bio-insecticide was evaluated based on potential entomopathogenic microorganisms used in the microbial suspension. The bio-insecticide consisted of entomopathogenic fungal and bacterial suspensions. The experiment was carried out in chili cultivation area in Situ Gede, Bogor. The application used spray method with multiple various doses. The observation showed that the plant treated with spore suspensions of entomopathogenic fungi Metarhizium sp. T4B23, B2-2, and cell suspensions of entomopathogenic bacteria Bt + SP4, were able to resist against insect pests, such as whitefly, grasshopper, and armyworm. In addition, the treated plant had more vigorous growth and yield than the control treatment.

The Biocontrol Agent and Insect Pathogen Photorhabdus luminescens Interacts with Plant Roots.

The number of sustainable agriculture techniques to improve pest management and environmental safety is rising, as biological control agents are used to enhance disease resistance and abiotic stress tolerance in crops. Here, we investigated the capacity of the Photorhabdus luminescens secondary variant to react to plant root exudates and their behavior toward microorganisms in the rhizosphere. P. luminescens is known to live in symbiosis with entomopathogenic nematodes (EPNs) and to be highly pathogenic toward insects. The P. luminescens-EPN relationship has been widely studied, and this combination has been used as a biological control agent; however, not much attention has been paid to the putative lifestyle of P. luminescens in the rhizosphere. We performed transcriptome analysis to show how P. luminescens responds to plant root exudates. The analysis highlighted genes involved in chitin degradation, biofilm regulation, formation of flagella, and type VI secretion system. Furthermore, we provide evidence that P. luminescens can inhibit growth of phytopathogenic fungi. Finally, we demonstrated a specific interaction of P. luminescens with plant roots. Understanding the role and the function of this bacterium in the rhizosphere might accelerate the progress in biocontrol manipulation and elucidate the peculiar mechanisms adopted by plant growth-promoting rhizobacteria in plant root interactions.IMPORTANCE Insect-pathogenic Photorhabdus luminescens bacteria are widely used in biocontrol strategies against pests. Very little is known about the life of these bacteria in the rhizosphere. Here, we show that P. luminescens can specifically react to and interact with plant roots. Understanding the adaptation of P. luminescens in the rhizosphere is highly important for the biotechnological application of entomopathogenic bacteria and could improve future sustainable pest management in agriculture.

The Alternative Sigma Factor SigB Is Required for the Pathogenicity of Bacillus thuringiensis

To adapt to changing and potentially hostile environments, bacteria can activate the transcription of genes under the control of alternative sigma factors, such as SigB, a master regulator of the general stress response in several Gram-positive species. Bacillus thuringiensis is a Gram-positive spore-forming invertebrate pathogen whose life cycle includes a variety of environments, including plants and the insect hemocoel or gut. Here, we assessed the role of SigB during the infectious cycle of B. thuringiensis in a Galleria mellonella insect model. We used a fluorescent reporter coupled to flow cytometry and showed that SigB was activated in vivo We also showed that the pathogenicity of the ΔsigB mutant was severely affected when inoculated via the oral route, suggesting that SigB is critical for B. thuringiensis adaptation to the gut environment of the insect. We could not detect an effect of the sigB deletion on the survival of the bacteria or on their sporulation efficiency in the cadavers. However, the gene encoding the pleiotropic regulator Spo0A was upregulated in the ΔsigB mutant cells during the infectious process.IMPORTANCE Pathogenic bacteria often need to transition between different ecosystems, and their ability to cope with such variations is critical for their survival. Several Gram-positive species have developed an adaptive response mediated by the general stress response alternative sigma factor SigB. In order to understand the ecophysiological role of this regulator in Bacillus thuringiensis, an entomopathogenic bacterium widely used as a biopesticide, we sought to examine the fate of a ΔsigB mutant during its life cycle in the natural setting of an insect larva. This allowed us, in particular, to show that SigB was activated during infection and that it was required for the pathogenicity of B. thuringiensis via the oral route of infection.

Immunosuppressive Activities of Novel PLA2 Inhibitors from Xenorhabdus hominickii, an Entomopathogenic Bacterium.

Simple SummaryInsect immune responses defend fatal attacks from entomopathogens. A Gram-negative Xenorhabdus hominickii exhibits high entomopathogenicity against lepidopteran insects. During the pathogenic processes, the bacteria suppress host insect immune responses by inhibiting phospholipase A2 (PLA2) enzyme activity with the bacterial secondary metabolites. PLA2 catalyzes eicosanoid biosynthesis. Eicosanoids mediate both cellular and humoral immune responses against various insect pathogens. This study identified eight different PLA2 inhibitors from the bacterial culture broth. Butanol extract of the culture broth possessed high potency to inhibit PLA2 activity. Subsequent fractionations led to identification of eight different compounds. The synthetic compounds also showed PLA2 inhibition and insecticidal activities. Furthermore, the addition of the bacterial PLA2 inhibitors significantly enhance other bacterial pathogenicity, suggesting its potential to be applied for developing novel insecticides. Eicosanoids mediate both cellular and humoral immune responses in insects. Phospholipase A2 (PLA2) catalyzes the first committed step in eicosanoid biosynthesis. It is a common pathogenic target of two entomopathogenic bacteria, Xenorhabdus and Photorhabdus. The objective of this study was to identify novel PLA2 inhibitors from X. hominickii and determine their immunosuppressive activities. To identify novel PLA2 inhibitors, stepwise fractionation of X. hominickii culture broth and subsequent enzyme assays were performed. Eight purified fractions of bacterial metabolites were obtained. Gas chromatography and mass spectrometry (GC-MS) analysis predicted that the main components in these eight fractions were 2-cyanobenzoic acid, dibutylamine, 2-ethyl 1-hexanol, phthalimide (PM), dioctyl terephthalate, docosane, bis (2-ethylhexyl) phthalate, and 3-ethoxy-4-methoxyphenol (EMP). Their synthetic compounds inhibited the activity of PLA2 in hemocytes of a lepidopteran insect, Spodoptera exigua, in a dose-dependent manner. They also showed significant inhibitory activities against immune responses such as prophenoloxidase activation and hemocytic nodulation of S. exigua larvae, with PM and EMP exhibiting the most potent inhibitory activities. These immunosuppressive activities were specific through PLA2 inhibition because an addition of arachidonic acid, a catalytic product of PLA2, significantly rescued such suppressed immune responses. The two most potent compounds (PM and EMP) showed significant insecticidal activities after oral administration. When the compounds were mixed with Bacillus thuringiensis (Bt), they markedly increased Bt pathogenicity. This study identified eight PLA2 inhibitors from bacterial metabolites of X. hominickii and demonstrated their potential as novel insecticides.

Potential for a biopesticide bait to control black beetle, Heteronychus arator (Coleoptera: Scarabaeidae).

Yersinia entomophaga is an entomopathogenic bacterium that is active against scarab beetles, among other insects. In New Zealand, the African black beetle, Heteronychus arator (Coleoptera: Scarabaeidae), is a major pest of pastures and arable crops but very few control options exist and no insecticides are registered for use in established pastures. In laboratory bioassays, H. arator adults were susceptible to a bait containing Y. entomophaga at low doses. This bait was more effective against H. arator adults during spring than autumn in small-scale field plots (320 mm diameter). A large-scale field trial (40 × 40 m plots) reduced adult numbers substantially: approximately twice as many beetles were captured in pitfall traps from untreated plots compared with plots treated with the Y. entomophaga bait at 70 kg ha-1 . This single bait application in spring also reduced subsequent larval populations in summer. Heteronychus arator is a difficult pest to manage using chemical insecticides. This biopesticide with Y. entomophaga as the active ingredient offers a new solution for New Zealand pastures, with potential for application to other crops affected by H. arator and for control of other pests. © 2020 Society of Chemical Industry.

Heptabladed β‐propeller lectins PLL2 and PHL from Photorhabdus spp. recognize O‐methylated sugars and influence the host immune system

O-methylation is an unusual sugar modification with a function that is not fully understood. Given its occurrence and recognition by lectins involved in the immune response, methylated sugars were proposed to represent a conserved pathogen-associated molecular pattern. We describe the interaction of O-methylated saccharides with two β-propeller lectins, the newly described PLL2 from the entomopathogenic bacterium Photorhabduslaumondii, and its homologue PHL from the related human pathogen Photorhabdusasymbiotica. The crystal structures of PLL2 and PHL revealed up to 10 out of 14 potential binding sites per protein subunit to be occupied with O-methylated structures. The avidity effect strengthens the interaction by 4 orders of magnitude. PLL2 and PHL also interfere with the early immune response by modulating the production of reactive oxygen species and phenoloxidase activity. Since bacteria from Photorhabdus spp. have a complex life cycle involving pathogenicity towards different hosts, the involvement of PLL2 and PHL might contribute to the pathogen overcoming insect and human immune system defences in the early stages of infection. DATABASES: Structural data are available in PDB database under the accession numbers 6RG2, 6RGG, 6RFZ, 6RG1, 6RGU, 6RGW, 6RGJ, and 6RGR.

Evaluation of insecticidal activity of entomopathogenic bacteria Photorhabdus and Xenorhabdus against shoot and fruit borer Earias vittella (Lepidoptera: Noctuidae) of vegetable crops

The shoot and fruit borer, Earias vittella is one of the major polyphagous pest prefer various host plants attacking almost 38 plant species and causes yield loss of 15-45% in vegetable crops annually in India. In this study Entomopathogenic bacteria (EPB) were used for biocontrol larvae of Earias vittella under in vitro condition. Whole cell culture and cell supernatant of EPB was screened for insecticidal activity against the larvae and results has shown that the lethality of larvae started after 12-24h of treatment. The percent mortality treated with intact cell was significantly higher in larvae treated with EPB3 with 90% mortality at 72h followed by EPB1 and EPB3. The larvae treated with cell supernatant of EPB had shown lethality in the range of the mortality of larvae where in the range of 50-70% at 72h of treatment and there was no significant difference among the bacteria treated. The LD50 value represent the concentration of cells required for the 50% population to be lethal and EPB3 had expressed significantly lower concentration of 4.28x104 CFU / ml followed by EPB9 and EPB8. The LD50 value for the larvae treated with cell supernatant were in the range of 1010 to 1012 CFU / ml. The larvae treated with EPB3 cell culture has taken significantly less time for mortality of fifty percent of population with a media lethal time (LT50) of 24h followed by EPB1 (30h) and EPB8 (32h). Among all the isolates EPB3 (Xenorhabdus nematophila) and EPB1 (Photorhabdus luminescens) had more virulence against the Earias vittella and can be further tested for biocontrol efficiency under greenhouse and field conditions.

The Investigation of the Biological Control of Icerya purchasi Maskell, 1878 (Hemiptera: Margarodidae) with Entomopathogenic Fungi and Bacteria

Cottony cushion scale Icerya purchasi Maskell, 1878 (Hemiptera: Margarodidae) is an important pest that inhibits the plant growth and development by sap sucking of the plants, and causes sooty mold in more than 200 plant species, especially in citrus plantation. The present study investigated the biological control of the nymphs and adult I. purchasi, which densely populates the mimosa plants (Acacia dealbata) in Artvin, Turkey. For this purpose, one fungal isolate [Beauveria bassiana (ET 10)] and eight bacterial strains [Brevibacillus brevis (CP-1), Bacillus thuringiensis subsp. kenyae (FDP-8, FDP-42), B. thuringiensis (FDP-1), B. sphaericus (FD-49), B. pumilus (TV-67C), Pseudomonas fluorescens (RK-1773) and B. atrophaeus (RK-1774)] were assessed against the nymphs and adult of I. purchasi under controlled conditions. Fungal and bacterial suspensions were sprayed onto 20 nymphs and 20 adults of I. purchasi in plastic boxes. The death rates of the nymphs and adults were recorded. The B. bassiana (ET 10) caused a death up to 100% and 80% in nymphs and adults, respectively. Moreover, P. flourescens (RK 1773) caused 90.5% death of nymphs and B. thuringiensis subsp. kenyae (FDP-42) presented 88.5% death to the nymphs of I. purchase. However, the use of the bacterial strains was not much successful against the adults, as compared to the nymphs.

When Appearance Misleads: The Role of the Entomopathogen Surface in the Relationship with Its Host.

Currently, potentially harmful insects are controlled mainly by chemical synthetic insecticides, but environmental emergencies strongly require less invasive control techniques. The use of biological insecticides in the form of entomopathogenic organisms is undoubtedly a fundamental resource for the biological control of insect pests in the future. These infectious agents and endogenous parasites generally act by profoundly altering the host’s physiology to death, but their success is closely related to the neutralization of the target insect’s immune response. In general, entomopathogen parasites, entomopathogenic bacteria, and fungi can counteract immune processes through the effects of secretion/excretion products that interfere with and damage the cells and molecules typical of innate immunity. However, these effects are observed in the later stages of infection, whereas the risk of being recognized and neutralized occurs very early after penetration and involves the pathogen surface components and molecular architecture; therefore, their role becomes crucial, particularly in the earliest pathogenesis. In this review, we analyze the evasion/interference strategies that entomopathogens such as the bacterium Bacillus thuringiensis, fungi, nematocomplexes, and wasps implement in the initial stages of infection, i.e., the phases during which body or cell surfaces play a key role in the interaction with the host receptors responsible for the immunological discrimination between self and non-self. In this regard, these organisms demonstrate evasive abilities ascribed to their body surface and cell wall; it appears that the key process of these mechanisms is the capability to modify the surface, converting it into an immunocompatible structure, or interaction that is more or less specific to host factors.

MAPK-dependent hormonal signaling plasticity contributes to overcoming Bacillus thuringiensis toxin action in an insect host

The arms race between entomopathogenic bacteria and their insect hosts is an excellent model for decoding the intricate coevolutionary processes of host-pathogen interaction. Here, we demonstrate that the MAPK signaling pathway is a general switch to trans-regulate differential expression of aminopeptidase N and other midgut genes in an insect host, diamondback moth (Plutella xylostella), thereby countering the virulence effect of Bacillus thuringiensis (Bt) toxins. Moreover, the MAPK cascade is activated and fine-tuned by the crosstalk between two major insect hormones, 20-hydroxyecdysone (20E) and juvenile hormone (JH) to elicit an important physiological response (i.e. Bt resistance) without incurring the significant fitness costs often associated with pathogen resistance. Hormones are well known to orchestrate physiological trade-offs in a wide variety of organisms, and our work decodes a hitherto undescribed function of these classic hormones and suggests that hormonal signaling plasticity is a general cross-kingdom strategy to fend off pathogens.

Bioactive Excreted/Secreted Products of Entomopathogenic Nematode Heterorhabditis bacteriophora Inhibit the Phenoloxidase Activity during the Infection.

Entomopathogenic nematodes (EPNs) are efficient insect parasites, that are known for their mutualistic relationship with entomopathogenic bacteria and their use in biocontrol. EPNs produce bioactive molecules referred to as excreted/secreted products (ESPs), which have come to the forefront in recent years because of their role in the process of host invasion and the modulation of its immune response. In the present study, we confirmed the production of ESPs in the EPN Heterorhabditis bacteriophora, and investigated their role in the modulation of the phenoloxidase cascade, one of the key components of the insect immune system. ESPs were isolated from 14- and 21-day-old infective juveniles of H. bacteriophora, which were found to be more virulent than newly emerged nematodes, as was confirmed by mortality assays using Galleria mellonella larvae. The isolated ESPs were further purified and screened for the phenoloxidase-inhibiting activity. In these products, a 38 kDa fraction of peptides was identified as the main candidate source of phenoloxidase-inhibiting compounds. This fraction was further analyzed by mass spectrometry and the de novo sequencing approach. Six peptide sequences were identified in this active ESP fraction, including proteins involved in ubiquitination and the regulation of a Toll pathway, for which a role in the regulation of insect immune response has been proposed in previous studies.

Pathogenicity of aerobic bacteria isolated from honeybees (Apis mellifera) in Ordu Province

The honeybee (Apis mellifera) is an important pollinator insect. Any pathogenic infection in this beneficial insect is undesirable. In this study, bacterial diversity in beehives was investigated to determine the potential of pathogenic bacteria in honeybees. To do this, bacterial isolations were carried out from dead and diseased adult bees collected from 9 districts in Ordu Province in Turkey.Twenty species of pathogenic bacteria, 18 of which were nonsporeforming Staphylococcus lentus, Klebsiella oxytoca, Citrobacter freundii, Leucanostoc mesenteroides ssp. cremoris, Kocuria rosea, Kocuria kristinae, Sphingomonas paucimobilis slashline, Burkholderia cepacia, Leucanostoc mesenteroides ssp. dextranicum,Hafnia alvei, Escherichia coli, Aeromonas salmonicida, Citrobacter braakii, Pantoea agglomerans, Streptococcus equi ssp. zooepidemicus, Staphylococcus pseudintermedius, Staphylococcus lugdunesis and Staphylococcus vitulinus and 2 sporeforming Bacillus licheniformis and Paenibacillus polymyxa, were isolated and identified from the honeybees. The infectivity of these bacteria were also documented with bioassay experiments on the healthy bees.The highest insecticidal effectwas determinedwith Bacillus licheniformis (84%), Escherichia coli (84%), and Streptococcus equi ssp. zooepidemicus (80%) on the adult honeybees.This result confirms that the honeybee contains a very large number of bacterial species and that the majority of them are pathogenic for the species in Turkey. In addition, some of the entomopathogenic bacteria used for biological control can have negative impact on this economically important insect.