Insecticidal activity of the metalloprotease AprA occurs through suppression of host cellular and humoral immunity

Pseudomonas mosselii: a potential alternative for managing pyrethroid-resistant Aedes aegypti

BACKGROUND

Aedes aegypti is a widespread mosquito in tropical and subtropical regions that causes significant mortality and morbidity in humans by transmitting diseases, such as dengue fever and Zika virus disease. Synthetic insecticides, such as pyrethroids, have been used to control Ae. aegypti, but these insecticides can also affect nontarget organisms and contaminate soil and water. This study aimed to investigate the mosquitocidal activity of Pseudomonas mosselii isolated from pond sludge against larvae of Ae. aegypti.

RESULTS

Based on the initial results, similar time-course profiles were obtained for the mosquitocidal activity of the bacterial culture and its supernatant, and the pellet resuspended in Luria-Bertani (LB) medium also showed delayed toxicity. These results imply that the toxic component can be released into the medium from live bacteria. Further research indicated that the toxic component appeared in the supernatant approximately 4 h after a 3-mL stock was cultured in 200 mL of LB medium. The stabilities of the P. mosselii culture and supernatant stored at different temperatures were also evaluated, and the best culture stability was obtained at 28 °C and supernatant stability at 4 °C. The bacterial culture and supernatant were toxic to larvae and pupae of not only susceptible Ae. aegypti but also pyrethroid-resistant strains.

CONCLUSION

This study highlights the value of the mosquitocidal activity of P. mosselii, which has potential as an alternative insecticide to control pyrethroid-resistant Ae. aegypti in the field. © 2024 Society of Chemical Industry.

Ingested soil bacteria breach gut epithelia and prime systemic immunity in an insect

Insects lack acquired immunity and were thought to have no immune memory, but recent studies reported a phenomenon called immune priming, wherein sublethal dose of pathogens or nonpathogenic microbes stimulates immunity and prevents subsequential pathogen infection. Although the evidence for insect immune priming is accumulating, the underlying mechanisms are still unclear. The bean bug Riptortus pedestris acquires its gut microbiota from ambient soil and spatially structures them into a multispecies and variable community in the anterior midgut and a specific, monospecies Caballeronia symbiont population in the posterior region. We demonstrate that a particular Burkholderia strain colonizing the anterior midgut stimulates systemic immunity by penetrating gut epithelia and migrating into the hemolymph. The activated immunity, consisting of a humoral and a cellular response, had no negative effect on the host fitness, but on the contrary protected the insect from subsequent infection by pathogenic bacteria. Interruption of contact between the Burkholderia strain and epithelia of the gut weakened the host immunity back to preinfection levels and made the insects more vulnerable to microbial infection, demonstrating that persistent acquisition of environmental bacteria is important to maintain an efficient immunity.

Defence response of Galleria mellonella larvae to oral and intrahemocelic infection with Pseudomonasentomophila

We report differences in the course of infection of G. mellonella larvae with P. entomophila via intrahemocelic and oral routes. Survival curves, larval morphology, histology, and induction of defence response were investigated. Larvae injected with 10 and 50 cells of P. entomophila activated a dose-dependent immune response, which was manifested by induction of immune-related genes and dose-dependent defence activity in larval hemolymph. In contrast, after the oral application of the pathogen, antimicrobial activity was detected in whole hemolymph of larvae infected with the 103 but not 105 dose in spite of the induction of immune response manifested as immune-relevant gene expression and defence activity of electrophoretically separated low-molecular hemolymph components. Among known proteins induced after the P. entomophila infection, we identified proline-rich peptide 1 and 2, cecropin D-like peptide, galiomycin, lysozyme, anionic peptide 1, defensin-like peptide, and a 27 kDa hemolymph protein. The expression of the lysozyme gene and the amount of protein in the hemolymph were correlated with inactivity of hemolymph in insects orally infected with a higher dose of P. entomophila, pointing to its role in the host-pathogen interaction.

Unveiling the Secrets of Calcium-Dependent Proteins in Plant Growth-Promoting Rhizobacteria: An Abundance of Discoveries Awaits

The role of Calcium ions (Ca2+) is extensively documented and comprehensively understood in eukaryotic organisms. Nevertheless, emerging insights, primarily derived from studies on human pathogenic bacteria, suggest that this ion also plays a pivotal role in prokaryotes. In this review, our primary focus will be on unraveling the intricate Ca2+ toolkit within prokaryotic organisms, with particular emphasis on its implications for plant growth-promoting rhizobacteria (PGPR). We undertook an in silico exploration to pinpoint and identify some of the proteins described in the existing literature, including prokaryotic Ca2+ channels, pumps, and exchangers that are responsible for regulating intracellular Calcium concentration ([Ca2+]i), along with the Calcium-binding proteins (CaBPs) that play a pivotal role in sensing and transducing this essential cation. These investigations were conducted in four distinct PGPR strains: Pseudomonas chlororaphis subsp. aurantiaca SMMP3, P. donghuensis SVBP6, Pseudomonas sp. BP01, and Methylobacterium sp. 2A, which have been isolated and characterized within our research laboratories. We also present preliminary experimental data to evaluate the influence of exogenous Ca2+ concentrations ([Ca2+]ex) on the growth dynamics of these strains.

Enterobacter Strain IPPBiotE33 Displays a Synergistic Effect with Bacillus thuringiensis Bt185

The discovery and isolation of new non-Bt insecticidal bacteria and genes are significant for the development of new biopesticides against coleopteran pests. In this study, we evaluated the insecticidal activity of non-Bt insecticidal bacteria, PPBiotE33, IPPBiotC41, IPPBiotA42 and IPPBiotC43, isolated from the peanut rhizosphere. All these strains showed insecticidal activity against first- and third-instar larvae of Holotrichia parallela, Holotrichia oblita, Anomala corpulenta and Potosia brevitarsis. IPPBiotE33 showed the highest toxicity among the four strains and exhibited virulence against Colaphellus bowringi. The genome of IPPBiotE33 was sequenced, and a new protein, 03673, with growth inhibition effects on C. bowringi was obtained. In addition, IPPBiotE33 had a synergistic effect with Bacillus thuringiensis Bt185 against H. parallela in bioassays and back-inoculation experiments with peanut seedlings. IPPBiotE33 induced a decrease in hemocytes and an increase in phenol oxidase activity in H. parallela hemolymph, known as the immunosuppressive effect, which mediated synergistic activity with Bt185. This study increased our knowledge of the new insecticidal strain IPPBiotE33 and shed new light on the research on new insecticidal coaction mechanisms and new blended pesticides.

Phages for treatment Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is denoted as one of the highly threatening bacteria to the public health. It has acquired many virulent factors and resistant genes that make it difficult to control with conventional antibiotics. Thus, bacteriophage therapy (phage therapy) is a proposed alternative to antibiotics to fight against multidrug-resistant P. aeruginosa. Many phages have been isolated that exhibit a broad spectrum of activity against P. aeruginosa. In this chapter, the common virulent factors and the prevalence of antibiotic-resistance genes in P. aeruginosa were reported. In addition, recent efforts in the field of phage therapy against P. aeruginosa were highlighted, including wild-type phages, genetically modified phages, phage cocktails, and phage in combination with antibiotics against P. aeruginosa in the planktonic and biofilm forms. Recent regulations on phage therapy were also covered in this chapter.

Outer membrane vesicles from bacteria: Role and potential value in the pathogenesis of chronic respiratory diseases

Infectious diseases are the leading cause of death in both adults and children, with respiratory infections being the leading cause of death. A growing body of evidence suggests that bacterially released extracellular membrane vesicles play an important role in bacterial pathogenicity by targeting and (de)regulating host cells through the delivery of nucleic acids, proteins, lipids, and carbohydrates. Among the many factors contributing to bacterial pathogenicity are the outer membrane vesicles produced by the bacteria themselves. Bacterial membrane vesicles are being studied in more detail because of their potential role as deleterious mediators in bacterial infections. This review provides an overview of the most current information on the emerging role of bacterial membrane vesicles in the pathophysiology of pneumonia and its complications and their adoption as promising targets for future preventive and therapeutic approaches.

Bactericidal Effect of Pseudomonas oryziphila sp. nov., a Novel Pseudomonas Species Against Xanthomonas oryzae Reduces Disease Severity of Bacterial Leaf Streak of Rice

Pseudomonas is a diverse genus of Gammaproteobacteria with increasing novel species exhibiting versatile trains including antimicrobial and insecticidal activity, as well as plant growth-promoting, which make them well suited as biocontrol agents of some pathogens. Here we isolated strain 1257 that exhibited strong antagonistic activity against two pathovars of Xanthomonas oryzae, especially X. oryzae pv. oryzicola (Xoc) responsible for the bacterial leaf streak (BLS) in rice. The phylogenetic, genomic, physiological, and biochemical characteristics support that strain 1257 is a representative of a novel Pseudomonas species that is most closely related to the entomopathogenic bacterium Pseudomonas entomophila. We propose to name it Pseudomonas oryziphila sp. nov. Comparative genomics analyses showed that P. oryziphila 1257 possesses most of the central metabolic genes of two closely related strains P. entomophila L48 and Pseudomonas mosselii CFML 90-83, as well as a set of genes encoding the type IV pilus system, suggesting its versatile metabolism and motility properties. Some features, such as insecticidal toxins, phosphate solubilization, indole-3-acetic acid, and phenylacetic acid degradation, were disclosed. Genome-wide random mutagenesis revealed that the non-ribosomal peptide catalyzed by LgrD may be a major active compound of P. oryziphila 1257 against Xoc RS105, as well as the critical role of the carbamoyl phosphate and the pentose phosphate pathway that control the biosynthesis of this target compound. Our findings demonstrate that 1257 could effectively inhibit the growth and migration of Xoc in rice tissue to prevent the BLS disease. To our knowledge, this is the first report of a novel Pseudomonas species that displays a strong antibacterial activity against Xoc. The results suggest that the P. oryziphila strain could be a promising biological control agent for BLS.

The M35 Metalloprotease Effector FocM35_1 Is Required for Full Virulence of Fusarium oxysporum f. sp. cubense Tropical Race 4

Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana, the most devastating disease on a banana plant. The genome of Foc TR4 encodes many candidate effector proteins. However, little is known about the functions of these effector proteins on their contributions to disease development and Foc TR4 virulence. Here, we discovered a secreted metalloprotease, FocM35_1, which is an essential virulence effector of Foc TR4. FocM35_1 was highly upregulated during the early stages of Foc TR4 infection progress in bananas. The FocM35_1 knockout mutant compromised the virulence of Foc TR4. FocM35_1 could interact with the banana chitinase MaChiA, and it decreased banana chitinase activity. FocM35_1 induced cell death in Nicotiana benthamiana while suppressing the INF1-induced hypersensitive response (HR), and its predicted enzymatic site was required for lesion formation and the suppression to INF1-induced HR on N. benthamiana leaves. Importantly, treatment of banana leaves with recombinant FocM35_1 accelerates Foc TR4 infection. Collectively, our study provides evidence that metalloprotease effector FocM35 seems to contribute to pathogen virulence by inhibiting the host immunity.

Accurate Analysis of Tricarboxylic Acid Cycle Metabolites and Anion Components in Hemocytes by IC-CD/ESI-MS for Quantifying Insecticide Impairment on Cellular Immunity in Mythimna separata

Insecticides are more broadly known to affect insect cellular immunity, but the components in hemocytes and their response to insecticide stress are still unknown. In this paper, a method based on trifluoroacetic acid extraction, followed by IC-CD/ESI-MS analysis, was developed to simultaneously determine tricarboxylic acid (TCA) cycle metabolites and anion components in hemocytes from Mythimna separata larvae. Validation gave excellent selectivity, recovery (88.7-107.6%), linear correlation (r² > 0.9961), precision (<3.89%), LOD (0.002-0.006 mg/L), LOQ (0.006-0.020 mg/L), and a short chromatographic run. The method was verified by administration of 4-((3-chloro-4-fluorophenyl)amino)-7-methoxyquinazolin-6-yl 3-(1,3-dioxoiso-indolin-2-yl) propanoate (QDP) or emamectin benzoate (EMB) to hemocytes in vitro and larvae in vivo. TCA metabolites including citrate, α-ketoglutarate, fumarate, malate, and oxaloacetate, and anions including acetate, oxalate, chloride, carbonate, and sulfate were identified and clearly separated. QDP and EMB showed a biphasic dose effect on TCA metabolites, and the contrary hormesis paralleled the different actions of QDP and EMB. The inhibition or improvement of cellular immunity depended on the QDP concentration. In conclusion, a highly sensitive, reliable, and robust method was developed, enabling the monitoring of hemocyte immunity by the quantification of TCA metabolites and anion components in minute hemocyte samples.

A M35 family metalloprotease is required for fungal virulence against insects by inactivating host prophenoloxidases and beyond

A diverse family of metalloproteases (MPs) is distributed in eukaryotes. However, the functions of MPs are still understudied. We report that seven MPs belonging to the M35 family are encoded in the genome of the insect pathogenic fungus Metarhizium robertsii. By gene deletions and insect bioassays, we found that one of the M35-family MPs, i.e. MrM35-4, is required for fungal virulence against insect hosts. MrM35-4 is a secretable enzyme and shows a proteolytic activity implicated in facilitating fungal penetration of insect cuticles. After gene rescue and overexpression, insect bioassays indicated that MrM35-4 contributes to inhibiting insect cuticular and hemocyte melanization activities. Enzymatic cleavage assays revealed that the recombinant prophenoloxidases PPO1 and PPO2 of Drosophila melanogaster could be clipped by MrM35-4 in a manner differing from a serine protease that can activate PPO activities. In addition, it was found that MrM35-4 is involved in suppressing antifungal gene expression in insects. Consistent with the evident apoptogenic effect of MrM35-4 on host cells, we found that the PPO mutant flies differentially succumbed to the infections of the wild-type and mutant strains of M. robertsii. Thus, MrM35-4 plays a multifaceted role beyond targeting PPOs during fungus-insect interactions, which represents a previously unsuspected strategy employed by Metarhizium to outmaneuver insect immune defenses.

Molecular characterization of pathogenesis involving the GAS 1 gene from Entomopathogenic fungus Lecanicillium lecanii and its virulence against the insect host Diaphorina citri

The entmopathogenic fungus Lecaniicillium lecanii is a naturally available biological control and it is considered to be one of the best mycoinsecticide agents against the destructive insect pest Diaphorina citri Kuwayama. The present study aimed to extract and characterize the toxic insecticidal protein from L. lecanii and to assess the toxicity level against the Asian citrus psyllid the vector of Huanglongbing disease (HLB), also called citrus greening. Extracts of a toxic substance from submerged batch culture examined by sodium dodecyl sulfate-poly-acrylamide (SDS-PAGE), had a molecular weight of 45 kDa. The most abundant toxic metabolite was subjected to HPLC to purify and identified it by mass spectrometry. Subsequently, metabolite toxicity was tested against D. citri at three different concentrations (1%, 2%, and 3%). The results showed that the highest concentration had a significant maximum mortality at 120 h post application. Furthermore, we investigated the expression of the GAS1 gene which was previously identified to have a role in pathogenicity in in vivo studies in adult insect psyllids. Results of this study indicated that expression of the virulence factor gene was present at three concentrations of the fungal suspension post inoculation. This is the first study to provide this novel approach for the characterization of fungal mediated synthesis of a cuticle degrading soluble protein against the insect D. citri. The present results provide strong information on the in vivo expression of the GAS1 gene involved in fungal virulence pertaining to penetration of the insect cuticle, but not to inhibiting the growth of the host.

Tobramycin reduces key virulence determinants in the proteome of Pseudomonas aeruginosa outer membrane vesicles

Tobramycin is commonly used to treat Pseudomonas aeruginosa lung infections in patients with Cystic Fibrosis (CF). Tobramycin treatment leads to increased lung function and fewer clinical exacerbations in CF patients, and modestly reduces the density of P. aeruginosa in the lungs. P. aeruginosa resides primarily in the mucus overlying lung epithelial cells and secretes outer membrane vesicles (OMVs) that diffuse through the mucus and fuse with airway epithelial cells, thus delivering virulence factors into the cytoplasm that modify the innate immune response. The goal of this study was to test the hypothesis that Tobramycin reduces the abundance of virulence factors in OMVs secreted by P. aeruginosa. Characterization of the proteome of OMVs isolated from control or Tobramycin-exposed P. aeruginosa strain PAO1 revealed that Tobramycin reduced several OMV-associated virulence determinants, including AprA, an alkaline protease that enhances P. aeruginosa survival in the lung, and is predicted to contribute to the inhibitory effect of P. aeruginosa on Phe508del-CFTR Cl^- secretion by primary human bronchial epithelial cells. Deletion of the gene encoding AprA reduced the inhibitory effect of P. aeruginosa on Phe508del-CFTR Cl^- secretion. Moreover, as predicted by our proteomic analysis, OMVs isolated from Tobramycin treated P. aeruginosa had a diminished inhibitory effect on Phe508del-CFTR Cl^- secretion compared to OMVs isolated from control P. aeruginosa. Taken together, our proteomic analysis of OMVs and biological validation suggest that Tobramycin may improve lung function in CF patients infected with P. aeruginosa by reducing several key virulence factors in OMVs that reduce CFTR Cl^- secretion, which is essential for bacterial clearance from the lungs.

Manipulation of the silkworm immune system by a metalloprotease from the pathogenic bacterium Pseudomonas aeruginosa

Antimicrobial peptide (AMP) production and melanization are two key humoral immune responses in insects. Induced synthesis of AMPs results from Toll and IMD signal transduction whereas melanization depends on prophenoloxidase (PPO) activation system. During invasion, pathogens produce toxins and other virulent factors to counteract host immune responses. Here we show that the pathways leading to PPO activation and AMP synthesis in the silkworm Bombyx mori are affected by a metalloprotease, named elastase B, secreted by Pseudomonas aeruginosa (PAO1). The metalloprotease gene (lasB) was expressed shortly after PAO1 cells had been injected into the larval silkworm hemocoel, leading to an increase of elastase activity. Injection of the purified PAO1 elastase B into silkworm hemolymph compromised PPO activation. In contrast, the protease caused a level increase of gloverin, an AMP in the hemolymph. To verify our results obtained using the purified elastase B, we infected B. mori with PAO1 ΔlasB mutant and found that PO activity in hemolymph of the PAO1 ΔlasB-infected larvae was significantly higher than that in the wild type-infected. The mutant-inhabited hemolymph had lower levels of gloverin and antimicrobial activity. PAO1 ΔlasB showed a decreased viability in the silkworm hemolymph whereas the host had a lower mortality. In addition, the effects caused by the ΔlasB mutant were restored by a complementary strain. These data collectively indicated that the elastase B produced by PAO1 is an important virulent factor that manipulates the silkworm immune system during infection.

Imidacloprid Pesticide Regulates Gynaikothrips uzeli (Thysanoptera: Phlaeothripidae) Host Choice Behavior and Immunity Against Lecanicillium lecanii (Hypocreales: Clavicipitaceae)

We attempted to develop an efficient management strategy against gall thrips (Gynaikothrips uzeli Zimmermann (Thysanoptera: Phlaeothripidae)) via the combined application of a systemic insecticide (imidacloprid) and an entomopathogenic fungus (Lecanicillium lecanii Zimmerman (Hypocreales: Clavicipitaceae)). The attraction of G. uzeli to Ficus microcarpa volatiles after imidacloprid treatment was weaker than for untreated plants, which could be due to modulation of volatile metabolite profiles by imidacloprid. The toxicity of L. lecanii against nymph and adult thrips was much higher for those that fed on plants treated with a 50% lethal concentration (LC50) of imidacloprid than for the controls. Phenoloxidase (PO) activity was significantly inhibited in treated G. uzeli, while hemocyte abundances were not different in treated and healthy individuals. Thus, imidacloprid impacted the PO-related humoral immunity of G. uzeli, but not their cellular immunity. Overall, F. microcarpa treated with imidacloprid at LC50 concentrations exhibited volatile profiles that decreased the attraction of G. uzeli and also indirectly increased the pathogenicity of L. lecanni by inhibiting the humoral immunity of gall thrips. The results reported here suggest that combined application of imidacloprid and L. lecanii could be used as a new integrated control strategy against gall thrips.

Secretion Systems and Secreted Proteins in Gram-Negative Entomopathogenic Bacteria: Their Roles in Insect Virulence and Beyond

Many Gram-negative bacteria have evolved insect pathogenic lifestyles. In all cases, the ability to cause disease in insects involves specific bacterial proteins exported either to the surface, the extracellular environment, or the cytoplasm of the host cell. They also have several distinct mechanisms for secreting such proteins. In this review, we summarize the major protein secretion systems and discuss examples of secreted proteins that contribute to the virulence of a variety of Gram-negative entomopathogenic bacteria, including Photorhabdus, Xenorhabdus, Serratia, Yersinia, and Pseudomonas species. We also briefly summarize two classes of exported protein complexes, the PVC-like elements, and the Tc toxin complexes that were first described in entomopathogenic bacteria.