Photorhabdus Temperata Research Articles

Genome sequences of Pseudomonas sp. strain FFPRI_1 and Photorhabdus temperata strain FFPRI_2, isolated from the entomopathogenic nematode, Heterorhabditis megidis.

The complete genome sequences of two bacteria isolated from an entomopathogenic nematode are reported. The genome sizes of Pseudomonas sp. strain FFPRI_1 and Photorhabdus temperata strain FFPRI_2 are 7,521,420 bp long with 63% G+C content and 5,483,510 bp long with 43.8% G+C content, respectively.

Enhancement of an entomopathogenic fungal virulence against the seedcorn maggot, Delia platura, by suppressing immune responses with a bacterial culture broth of Photorhabdus temperata subsp. temperata.

In Korea, there are two maggot species in the Delia genus that commonly infest the roots and stems of the Welsh onion, thus causing serious economic damage on the crop at the seedling stage. In this study, the seedcorn maggot (Delia platura) was detected in onion fields in two different localities in Korea. After overwintering, maggot infestations occurred throughout the entire growing seasons from transplantation to harvest, but their specific patterns of occurrence varied in the two localities examined. Entomopathogenic fungi induced significant virulence against the maggot larvae, in which a strain of Beauveria bassiana was effective, though it exhibited limited mortality in its insecticidal activity. To enhance this insecticidal activity, a culture broth from an entomopathogenic bacterium, Photorhabdus temperata temperata (Ptt), was added to B. bassiana treatment. The addition of Ptt broth significantly increased the insecticidal activity of B. bassiana in a dose-dependent manner. To elucidate this enhancement in insecticidal activity, the immunosuppressive activity of Ptt broth was assessed by identifying the immune responses of the seedcorn maggots. The seedcorn maggots possessed at least three different hemocytes with plasmatocytes, crystal cells, and lamellocytes. These hemocytes exhibited nodule formation in response to the fungal infection. In addition to the cellular immunity, the maggots exhibited inducible expressions of antimicrobial peptide (AMP) genes such as cecropin and defensin. The addition of Ptt broth suppressed the nodule formation and the AMP expressions in response to the fungal infection. Altogether, this study demonstrated the innate immune responses in a non-model insect, D. platura, along with the application of immunosuppression to develop a highly efficient biological control by enhancing the virulence of B. bassiana.

Topical treatment of adult house flies, Musca domestica L. (Diptera: Muscidae), with Beauveria bassiana in combination with three entomopathogenic bacteria

Abstract Biological control of house flies, Musca domestica L. (Diptera: Muscidae) has the potential to improve the efficacy and sustainability of integrated pest management. In a previous study, we demonstrated that three bacteria species (Serratia marcescens Bizio [Enterobacteriales: Enterobacteriaceae], Photorhabdus temperata Fischer-Le Saux et al. [Enterobacteriales: Enterobacteriaceae], and Pseudomonas protegens Ramette et al. [Pseudomonadales: Pseudomonadaceae]) are extremely virulent, inducing rapid morbidity and high mortality in adult house flies when injected into the hemocoel but show little effect when applied topically. Here we tested the hypothesis that topical application of these species in combination with the entompathogenic fungus Beauveria bassiana (Bals. Criv.) Vuill. (Hypocreales: Cordycipitaceae) would result in an increased and rapid mortality if fungal penetration of the fly cuticle allowed for increased delivery of the bacteria into the fly hemocoel. Bacteria and B. bassiana were tested either by application at the same time or by sequential application of the two pathogens 48 h apart. Results indicated little evidence for synergy between B. bassiana and any of the bacterial pathogens. However, P. protegens caused early mortality (<50 % at 3 days) when applied alone and in combination with B. bassiana. A modified disc diffusion assay indicated that P. temperata and P. protegens had inhibitory effects on the vegetative growth of B. bassiana suggesting the release of antifungal molecules by the bacteria. Results with P. protegens were sufficiently encouraging to warrant further investigation of this species and its associated toxins as house fly biological control tools.

Beware glowing cadavers: bioluminescence of nematode symbiont Photorhabdus protects nematode-infected host cadavers from nocturnal scavengers

Photorhabdus spp. are the only known terrestrial bioluminescent bacteria. We show that the bioluminescence produced by these bacteria reduces scavenging activity on the insect cadavers they colonize. Photorhabdus spp. are the symbiont of the insect pathogenic nematodes Heterorhabditis spp. Together they kill insects and colonize the cadaver. The function of their bioluminescence has been the subject of debate, but here for the first time we demonstrate an ecological benefit. In our experiments, fewer Photorhabdus temperata -infected cadavers than uninfected cadavers were scavenged, but only in dark conditions where their bioluminescence would be visible. This was the case both in the field and in laboratory experiments with Lehmannia valentiana slugs (the primary scavengers found in our field tests). We also show that L. valentiana is innately deterred from scavenging on uninfected cadavers in proximity to light imitating the bioluminescence of Photorhabdus, indicating that luminescence can be a deterrent independent of chemical cues. We propose a multimodal defence where bioluminescence works together with the chemical defences also produced by Photorhabdus to deter scavengers, such as slugs, from feeding on the host cadaver, with the potential for aposematism.

Manipulation of GameXPeptide synthetase gene expression by a promoter exchange alters the virulence of an entomopathogenic bacterium, Photorhabdus temperata temperata, by modulating insect immune responses.

An entomopathogenic bacterium, Photorhabdus temperata subsp. temperata, is mutualistic to its host nematode, Heterorhabditis megidis. The infective juvenile nematodes enter target insects through natural openings and release the symbiotic bacteria into the insect hemocoel. The released bacteria suppress the insect immune responses and cause septicemia through their secondary metabolites. GameXPeptide (GXP) is one of the common secondary metabolites of most Photorhabdus species and is produced by the catalytic activity of a specific non-ribosomal peptide synthetase called GxpS encoded by the gxpS gene. This study confirmed gxpS to be encoded in the P. temperata temperata genome and analyzed its expression during bacterial growth. LC-MS/MS analysis of the bacterial culture broth contained at least four different GXPs (GXP-A to GXP-D), in which GXP-A was the most abundant. To investigate GXP synthesis following gxpS expression, the gxpS promoter of P. temperata temperata was replaced with an inducible arabinose promoter by homologous recombination. The gxpS transcript levels in the mutant were altered by the addition of l-arabinose. Without the inducer, the gxpS transcript level was significantly lower compared to the wild type and produced significantly lower amounts of the four GXPs. The addition of the inducer to the mutant significantly increased gxpS expression and produced significantly higher levels of the four GXPs compared to the wild type. The metabolite extracts obtained from wild-type and mutant bacteria showed differential immunosuppressive activities according to their GXP contents against the cellular and humoral immune responses of a lepidopteran insect, Spodoptera exigua. Interestingly, the gxpS-mutant bacteria showed less insecticidal activity compared to the wild type, whereas the addition of GXP to the mutant significantly restored insecticidal activity. These results suggest that the gxpS gene encoded in P. temperata temperata is responsible for the production of at least four different GXPs, which play crucial roles in bacterial virulence.

The aptness of entompathogenic bacteria against sawtoothed grain beetle (Oryzaephilus surinamensis [L.]) (Coleoptera: Silvanidae) in dates under laboratory conditions

ObjectiveThe sawtoothed grain beetle, Oryzaephilus surinamensis (L). is known as one of the most devastating insect pests in stored date fruits, infrequently found in newly harvested date fruits and raisins but developed a high plenty in dry fruits particularly after long storage. Indiscriminate use of pesticides and fumigants to control insects have resulted in insecticide resistance, environmental hazards, residual toxicity, and pest resurgence so the control trends have been changed and particularly biological control agents like entomopathogenic bacteria Photorhabdus temperata and Xenorhabdus nematophila being used to manage sawtoothed grain beetle. MethodsDuring present study, the pathogenicity of P. temperata and X. nematophila was evaluated against this crucial pest of stored grains. The bacterial concentrations, 1 × 104, 1 × 105, 1 × 106, 1 × 107 and 1 × 108 cells/ml of both bacteria were prepared and used for the experiments. The prepared solutions were applied directly to the date fruits infested with sawtoothed grain beetles and data were recorded. ResultsSignificant results were observed for both bacterial treatments as the highest concentration of 108 cells/ml showed to be very effective against the beetle in terms of fecundity, adult emergence, and mortality. In terms of fecundity, 8.66 to 4.33 mean number of eggs were produced at bacterial P. temperata concentrations of 1 × 104 and 1 × 108 cells/ml, respectively. Similarly, the F1 adult emergence for P. temperata was recorded 15.33 and 9 adults at concentrations of 1 × 104 and 1 × 108 cells/ml, respectively. Results showed a similar trend for the X. nematophila species. ConclusionsThese results indicate that utilizing bacteria as biological control agents can be advantageous for reducing insect populations in storage facilities and preventing the loss of grains and date fruits that have been stored in storage.

Photorhabdus lux-operon heat shock-like regulation

For decades, transcription of Photorhabdus luminescens lux-operon was considered being constitutive. Therefore, this lux-operon has been used for measurements in non-specific bacterial luminescent biosensors. Here, the expression of Photorhabduslux-operon under high temperature was studied. The expression was researched in the natural strain Photorhabdus temperata and in the heterologous system of Escherichia coli. P. temperata FV2201 bacterium was isolated from soil in the Moscow region (growth optimum 28 °C). We showed that its luminescence significantly increases when the temperature rises to 34 °C. The increase in luminescence is associated with an increase in the transcription of luxCDABE genes, which was confirmed by RT-PCR. The promoter of the lux-operon of the related bacterium P. luminescens ZM1 from the forests of Moldova, being cloned in the heterologous system of E. coli, is activated when the temperature rises from room temperature to 42 °C. When heat shock is caused by ethanol addition, transcription of lux-operon increases only in the natural strain of P. temperata, but not in the heterologous system of E. coli cells. In addition, the activation of the lux-operon of P. luminescens persists in E. coli strains deficient in both the rpoH and rpoE genes. These results indicate the presence of sigma 32 and sigma 24 independent heat-shock-like mechanism of regulation of the lux-operon of P. luminescens in the heterologous E. coli system.

Entomopathogens as biological control of the mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae)

Mediterranean flour moth Ephestia kuehniella (Zeller, Lepidoptera: Pyralidae) is one of the most important insect pests that invade the stored grain of many grains around the world. Chemical control is a very preferred method in the fight of this pest. However, due to the economic, social and environmental damages of chemicals, the interest in biological control, which is an alternative method, is gradually increasing. Entomopathogens have very important in biological control and that cause desired infections in pests. Entomopathogens include many species such as viruses, bacteria, protists, fungi and nematodes. In recent years, entomopathogeic nematodes; Steinernema feltiae, Steinernema carpocapsae, Steinernema riobrave, Heterorhabditis bacteriophora, Heterorhabditis sp., Steinernema sp., and Xenorhabdus nematophila, entomopathogenic fungi; Paecilomyces fumosoroseus (=Isaria fumosorosea), Beuveria bassiana and Metarhizium anisopliae, entomopathogenic bacteria; Bacillus thuringiensis subsp. kurstaki, Photorhabdus temperata and Bacillus subtilis, entomopathogenic protists; Vairimorpha ephestiae, Leidyana ephestiae, Mattesia dispora and Mattesia oryzaephili, and virus; Nuclear Polyhedrosis Virus (NPV) were reported from E.kuehniella. In this review, it is aimed to evaluate the recent status of these entomopathogenic organisms found or tested for E. kuehniella

Total Synthesis of the Phosphorylated Zwitterionic Trisaccharide Repeating Unit of Photorhabdus temperata cinerea 3240.

Herein, we report the total synthesis of the phosphorylated zwitterionic trisaccharide repeating unit of Photorhabdus temperata subsp. cinerea 3240. The efficient route involves regio- and stereoselective assembly of trisaccharide with rare deoxyamino sugar AAT at the nonreducing end, late stage oxidation, and installation of a phosphate linker on the trisaccharide. The total synthesis was completed via a longest linear sequence of 24 steps in 6.5% overall yield.

Development of a cost-effective medium for Photorhabdus temperata bioinsecticide production from wastewater and exploration of performance kinetic

This study investigates the optimization of the culture conditions for enhancing Photorhabdus temperata biopesticide production using wastewater (WS4) as a raw material. Box-Behnken design (BBD) was used to evaluate the effects of carbon to nitrogen ratio (C/N), sodium chloride concentration and inoculum size on P. temperata biomass production and insecticidal activity. For an enhanced biopesticide production, the optimum operating conditions were as follows: inoculum size = 4%; C/N ratio = 12.5 and [NaCl] = 4 g/L for two responses. 1.95 and 2.75 fold improvements in oral toxicity and biomass production were respectively obtained in the cost-effective medium developed in this study (WS4 I) using the three variables at their optimal values. Under the optimized conditions, WS4 I-grown cells exhibited higher membrane integrity according to flow cytometry analysis since dead cells presented only 9.2% compared to 29.2% in WS4. From batch fermentations carried out in WS4 I and WS4, P. temperata kinetic parameters in terms of biomass production and substrate consumption rates were modeled. The obtained results showed that the maximum specific growth rate in WS4 I was of 0.43 h−1 while that obtained in WS4 was of 0.14 h−1. In addition, the efficiency of P. temperata to metabolize organic carbon was enhanced by optimizing the culture conditions. It reached 72.66% instead of 46.18% in the control fermentation after 10 h of incubation. Under the optimized conditions, P. temperata cells showed the highest specific consumption rate resulting in a toxin synthesis improvement.

Comparative In Silico Analysis of Randomly Selected Heat Shock Proteins in Caenorhabditis elegans and Photorhabdus temperata

Heat shock proteins (HSPs) such as HSP70A, HSP90 etc. (also known as Chaperons) play an important role in folding and unfolding of proteins, an assemblage of multiprotein complexes, transportation and sorting of proteins in subcellular compartments, cell cycle control, signaling pathways, protection against stress and programmed cell death. Studies have also linked heat shock proteins with a sudden rise in temperature, which can be related to anhydrobiosis in nematodes. Considering the significance of HSPs in nematodes and bacteria, the present study was designed for their in silico analysis in Caenorhabditis elegans and Photorhabdus temperata. The availability of a vast amount of sequence data generated through various bioinformatics tools, coupled with computational biology advancements, provides an ideal framework for silico gene expression and its analysis. A detailed in silico insight into these proteins include physicochemical properties, secondary structure prediction, homology modeling, and different models. The amino acid composition data were subjected to multivariate techniques, Pearson correlation, and phylogenetic analysis. In the present study, the authors characterized different HSPs according to different stability parameters and valid structures. A detailed in silico analysis of these proteins and prediction of their activity in different conditions can be very useful in both in vitro and in vivo experiments.

Acidic pretreatment as a chemical approach for enhanced Photorhabdus temperata bioinsecticide production from industrial wastewater

The chemical treatment of the wastewater used for the bioinsecticide production by the bacterium Photorhabdus temperata was investigated in this study. An improvement of the volatile suspended solids (VSS) solubilization along with an increase in protein, carbohydrate, reducing sugar and nitrogen concentrations were demonstrated after alkali and thermo-alkali hydrolysis. In contrast, the application of acidic and thermo-acidic pretreatments reduced the organic matter hydrolysis. Compared to untreated wastewater, the chemical oxygen demand (COD) solubilization and the heavy metal concentration, except manganese, were enhanced in all the chemically pretreated wastewaters. Although its low contribution in the solubilization of the wastewater organic matter, the acidic-pretreated wastewater showed the highest performance in supporting P. temperata biopesticide production. Indeed, using the acidic-pretreated wastewater as a fermentation medium decreased the lag phase, enhanced the growth of the strain K122 to reach a final biomass production of 20 × 108 cells/mL, increased culturable cell count to 262 × 106 cells/mL and improved oral toxicity against Ephestia kuehniella larvae by 68.4%. Among chemical pretreatments performed, the acidic hydrolysis was demonstrated to be the unique promising one for P. temperata bioinsecticide production due to its ability to reduce aromatic compounds as shown by Gas Chromatography-Mass Spectrometry (GC-MS) analysis.

Competition and Co-existence of Two Photorhabdus Symbionts with a Nematode Host

Photorhabdus spp. (Enterobacteriales: Morganellaceae) occur exclusively as symbionts of Heterorhabditis nematodes for which they provide numerous services, including killing insects and providing nutrition and defence within the cadavers. Unusually, two species (Photorhabdus cinerea and Photorhabdus temperata) associate with a single population of Heterorhabditis downesi at a dune grassland site. Building on previous work, we investigated competition between these two Photorhabdus species both at the regional (between insects) and local (within insect) level by trait comparison and co-culture experiments. There was no difference between the species with respect to supporting nematode reproduction and protection of cadavers against invertebrate scavengers, but P. cinerea was superior to P. temperata in several traits: faster growth rate, greater antibacterial and antifungal activity and colonisation of a higher proportion of nematodes in co-culture. Moreover, where both bacterial symbionts colonised single nematode infective juveniles, P. cinerea tended to dominate in numbers. Differences between Photorhabdus species were detected in the suite of secondary metabolites produced: P. temperata produced several compounds not produced by P. cinerea including anthraquinone pigments. Bioluminescence emitted by P. temperata also tended to be brighter than that from P. cinerea. Bioluminescence and pigmentation may protect cadavers against scavengers that rely on sight. We conclude that while P. cinerea may show greater local level (within-cadaver) competitive success, co-existence of the two Photorhabdus species in the spatially heterogeneous environment of the dunes is favoured by differing specialisations in defence of the cadaver against differing locally important threats.

Towards a new biological control approach for Photorhabdus temperata bioinsecticide production through the bioconversion of Tunisian industrial wastewater

A novel bioconversion approach of Tunisian wastewater to low-cost Photorhabdus temperata bioinsecticide is presented in this study. Our results showed that when cultured on the food industry wastewater (WS4), P. temperata cells exhibited oral toxicity of about 42%, which is the same as those cultured in complex medium (CM), used as control. Moreover, variants small colony polymorphism (Vsm) of the strain K122 was completely avoided after a prolonged incubation. However, viable but non-culturable (VBNC) state was enhanced with the maximum colony-forming units (CFU) count of 9 × 106 cells/mL obtained after 48 h of incubation in the WS4. According to flow cytometry analysis, almost 100% of P. temperata cells were viable until 48 h of incubation. The appearance of propidium iodide (PI) positively stained cells was observed after a prolonged incubation with a maximum of 17% of damaged cells in WS1. In order to follow the progress of P. temperata fermentation process carried out in industrial wastewater, we established for the first time, the mathematical relationship between total cell counts, CFU counts and oral toxicity of P. temperata strain K122. Indeed, irrespective of the medium used, the relationship between CFU count and total cell count followed a power law. Additionally, when plotting CFU count, or total cell count against toxicity, a semi-log linear relationship was obtained. Our results proved the efficiency of this bioconversion approach to produce bioinsecticide based on the entomopathogenic bacterium P. temperata, with practical benefits in terms of cost production and wastewater management.

Dual Oxidase-Derived Reactive Oxygen Species Against Bacillus thuringiensis and Its Suppression by Eicosanoid Biosynthesis Inhibitors.

Two entomopathogenic bacteria, Xenorhabdus and Photorhabdus, are known to be able to synthesize and secrete eicosanoid biosynthesis inhibitors (EIBs) that can enhance pathogenicity of Bacillus thuringiensis (Bt) against different target insects. Such enhancements can be explained by the suppression of immune responses in the hemocoel by EIBs. However, little is known about the role of EIBs in the defense against Bt pathogenicity in the gut. This study was focused on the role of insect gut immunity in the defense against Bt pathogenicity, in which the cooperative effect of bacterial metabolites was assessed. Screening 14 different bacterial strains, bacterial culture broth of Photorhabdus temperata subsp. temperata ANU101 (Ptt) gave the highest cooperative effect on Bt virulence along with significant inhibitory activity against phospholipase A2 (PLA2) of Plutella xylostella. In gut lumen, Ptt culture broth suppressed the generation of reactive oxygen species (ROS) induced by Bt treatment and facilitated bacterial growth, similar to vitamin E, an antioxidant. To analyze the ROS source, dual oxidase (Px-Duox) and NADPH-dependent oxidase (Px-Nox) genes were predicted from P. xylostella genome and their expressions were confirmed in larval gut. RNA interference (RNAi) of Px-Duox expression reduced ROS levels in both gut epithelium and lumen while RNAi of Px-Nox expression reduced ROS levels only in gut epithelium. Ptt extract significantly suppressed gene expression levels of Px-Duox and Px-Nox, leading to lower ROS concentrations in the gut lumen. Three commercial PLA2 inhibitors significantly increased the insecticidal activity of Bt by suppressing ROS levels in the gut lumen. These results indicate that Ptt extract containing EBIs can prevent up-regulation of ROS level in the midgut in response to Bt infection and enhance the virulence of Bt against P. xylostella.

Phototemtide A, a Cyclic Lipopeptide Heterologously Expressed from Photorhabdus temperata Meg1, Shows Selective Antiprotozoal Activity.

A new cyclic lipopeptide, phototemtide A (1), was isolated from Escherichia coli expressing the biosynthetic gene cluster pttABC from Photorhabdus temperata Meg1. The structure of 1 was elucidated by HR‐ESI‐MS and NMR experiments. The absolute configurations of amino acids and 3‐hydroxyoctanoic acid in 1 were determined by using the advanced Marfey's method and comparison after total synthesis of 1, respectively. Additionally, three new minor derivatives, phototemtides B–D (2–4), were identified by detailed HPLC–MS analysis. Phototemtide A (1) showed weak antiprotozoal activity against Plasmodium falciparum, with an IC50 value of 9.8 μm. The biosynthesis of phototemtides A–D (1–4) was also proposed.

Cloning and expression of the insecticidal toxin gene “tccB” from Photorhabdus temperata M1021 in Escherichia coli expression system

Abstract Photorhabdus spp. has a high molecular weight Tc toxin with insecticidal activity. These toxins have been suggested as an alternative to BT toxin from Bacillus thuringiensis. Herein, we constructed a cosmid library with the genome of M1021 and screened the Escherichia coli clones showing insect toxicity by injecting each clone into Galleria mellonella larvae. In a total of 1020 clones, one clone with high insecticidal activity was selected and the nucleotide sequence of the cosmid of the clone was determined. In cosmid PtC28, a gene with 87% homology to the tccB gene of Photorhabdus temperata was found. Consequently, we have isolated the tccB gene cassette from the M1021 and expressed in E. coli expression vectors. The toxin was produced in the form of inclusion bodies but the denatured and refolded recombinant TccB showed strong mortality to the G. mellonella larvae.

Structure, Biosynthesis, and Bioactivity of Photoditritide from Photorhabdus temperata Meg1.

A new cyclic peptide photoditritide (1), containing two rare amino acid d-homoarginine residues, was isolated from Photorhabdus temperata Meg1 after the nonribosomal peptide synthetase encoding gene pdtS was activated via promoter exchange. The structure of 1 was elucidated by HR-MS and NMR experiments. The absolute configurations of amino acids were determined according to the advanced Marfey's method after hydrolysis of 1. Bioactivity testing of 1 revealed potent antimicrobial activity against Micrococcus luteus with an MIC value of 3.0 μM and weak antiprotozoal activity against Trypanosoma brucei rhodesiense with an IC50 value of 13 μM. Additionally, the biosynthetic pathway of 1 was also proposed.

Mortality Effects of Three Bacterial Pathogens and Beauveria bassiana When Topically Applied or Injected Into House Flies (Diptera: Muscidae).

The house fly, Musca domestica L., is a global pest of public health and agricultural importance. The efficacy of conventional management has been waning due to increasing insecticide resistance. A potential management tool is the entomopathogenic fungus, Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae) (strain L90), although time-to-death is slower than desired by potential users. This research investigated the effectiveness of three gram-negative bacteria (Pseudomonas protegens Ramette (Psuedomonadales: Pseudomonadaceae) pf-5, Photorhabdus temperata Fischer-Le Saux (Enterobacteriales: Enterobacteriaceae) NC19, and Serratia marcescens Bizio (Enterobacteriales: Enterobacteriaceae) DB11) on house fly mortality when topically applied, compared to B. bassiana. Each pathogen's virulence was measured by injection into adult female house flies or by topical applications to their thorax. All bacterial strains were highly virulent after injection with 1 × 104 colony forming units (cfu), causing fly mortality within 24 h. Beauveria bassiana resulted in high mortality, 3 d postinjection at the high dose of 1 × 104 conidia/µl. Mortality due to topical treatments of P. temperata and S. marcescens was low even at the highest dose of 1 × 106 cfu/µl. Mortality after topical treatments with P. protegens was evident 4 d after application of 1 × 106 cfu/µl. Mortality from B. bassiana was low at 4 d but increased at 5 d. These results imply that P. protegens holds great potential as a biological control agent for incorporation into an integrated pest management program against adult house flies.

Eicosanoid mediation of immune responses at early bacterial infection stage and its inhibition by Photorhabdus temperata subsp. temperata, an entomopathogenic bacterium

An entomopathogenic bacterium Photorhabdus temperata subsp. temperata (Ptt) infects insect hemocoel by the vectoring activity of its symbiotic nematode, Heterorhabditis megidis. The bacterium induces host immunosuppression by inhibiting eicosanoid biosynthesis. This study investigated the role of eicosanoids in immune responses of the beet armyworm, Spodoptera exigua, in the early bacterial infection stage (first 3 hr postinfection [PI]). After infection with the nonpathogenic Escherichia coli (Ec), the bacterium maintained its population for the first 3 hr PI, then rapidly decreased in numbers. During the 3 hr PI of Ptt, this pathogenic bacterium also did not show any significant change in bacterial population. However, Ptt rapidly increased its population size after the initial lag phase, inducing fatal septicemia. This study further analyzed cellular and humoral immune responses of the beet armyworm during the initial 3 hr PI. During this early stage, challenge with Ec stimulated hemocyte-spreading behavior along with extensive F-actin growth. However, Ptt infection suppressed hemocyte spreading. Expression levels of three antimicrobial peptides (lysozyme, gloverin, and gallerimycin) were significantly inhibited during Ptt infection. Phospholipase A2 activity was significantly induced during the early infection stage of Ec, but not during Ptt infection. Addition of eicosanoid biosynthesis inhibitors significantly reversed the initial immunosuppression. These results suggest that, during the early infection stage, Ptt can shutdown eicosanoid biosynthesis which can prevent acute immune responses of host insects.