Differential infectivity of two Pseudomonas species and the immune response in the milkweed bug, Oncopeltus fasciatus (Insecta: Hemiptera)

Triphenylphosphonium Analogs of Short Peptide Related to Bactenecin 7 and Oncocin 112 as Antimicrobial Agents

Antimicrobial peptides (AMPs) have recently attracted attention as promising antibacterial agents capable of acting against resistant bacterial strains. In this work, an approach was applied, consisting of the conjugation of a peptide related to the sequences of bactenecin 7 (Bac7) and oncocin (Onc112) with the alkyl(triphenyl)phosphonium (alkyl-TPP) fragment in order to improve the properties of the AMP and introduce new ones, expand the spectrum of antimicrobial activity, and reduce the inhibitory effect on the eukaryotic translation process. Triphenylphosphonium (TPP) derivatives of a decapeptide RRIRPRPPYL were synthesized. It was comprehensively studied how the modification of the AMP affected the properties of the new compounds. It was shown that while the reduction in the Bac7 length to 10 a.a. residues dramatically decreased the affinity to bacterial ribosomes, the modification of the peptide with alkyl-TPP moieties led to an increase in the affinity. New analogs with structures that combined a decapeptide related to Bac7 and Onc112-Bac(1-10, R/Y)-and TPP attached to the C-terminal amino acid residue via alkylamide linkers, inhibited translation in vitro and were found to be more selective inhibitors of bacterial translation compared with eukaryotic translation than Onc112 and Bac7. The TPP analogs of the decapeptide related to Bac7 and Onc112 suppressed the growth of both Gram-negative bacteria, similar to Onc112 and Bac7, and Gram-positive ones, similar to alkyl-TPP derivatives, and also acted against some resistant laboratory strains. Bac(1-10, R/Y)-C2-TPP, containing a short alkylamide linker between the decapeptide and TPP, was transferred into the E. coli cells via the SbmA transporter protein. TPP derivatives of the decapeptide Bac(1-10, R/Y) containing either a decylamide or ethylamide linker caused B. subtilis membrane depolarization, similar to alkyl-TPP. The Bac(1-10, R/Y)-C2-TPP analog was proven to be non-toxic for mammalian cells using the MTT test.

Peptide-based molecules for the disruption of bacterial Hsp70 chaperones

DnaK is a chaperone that aids in nascent protein folding and the maintenance of proteome stability across bacteria. Due to the importance of DnaK in cellular proteostasis, there have been efforts to generate molecules that modulate its function. In nature, both protein substrates and antimicrobial peptides interact with DnaK. However, many of these ligands interact with other cellular machinery as well. Recent work has sought to modify these peptide scaffolds to create DnaK-selective and species-specific probes. Others have reported protein domain mimics of interaction partners to disrupt cellular DnaK function and high-throughput screening approaches to discover clinically-relevant peptidomimetics that inhibit DnaK. The described work provides a foundation for the design of new assays and molecules to regulate DnaK activity.

Conjugates of Desmycosin with Fragments of Antimicrobial Peptide Oncocin: Synthesis, Antibacterial Activity, Interaction with Ribosome

Design and synthesis of conjugates consisting of the macrolide antibiotic desmycosin and fragments of the antibacterial peptide oncocin were performed in attempt to develop new antimicrobial compounds. New compounds were shown to bind to the E. coli 70S ribosomes, to inhibit bacterial protein synthesis in vitro, as well as to suppress bacterial growth. The conjugates of N-terminal hexa- and tripeptide fragments of oncocin and 3,2',4''-triacetyldesmycosin were found to be active against some strains of macrolide-resistant bacteria. By simulating molecular dynamics of the complexes of these compounds with the wild-type bacterial ribosomes and with ribosomes, containing A2059G 23S RNA mutation, the specific structural features of their interactions were revealed.

Effect of amino acid substitutions on 70S ribosomal binding, cellular uptake, and antimicrobial activity of oncocin Onc112

Proline‐rich antimicrobial peptides (PrAMPs) are promising candidates for the treatment of infections caused by high‐priority human pathogens. Their mode of action consists of (I) passive diffusion across the outer membrane, (II) active transport through the inner membrane, and (III) inhibition of protein biosynthesis by blocking the exit tunnel of the 70S ribosome. We tested whether in vitro data on ribosomal binding and bacterial uptake could predict the antibacterial activity of PrAMPs against Gram‐negative and Gram‐positive bacteria. Ribosomal binding and bacterial uptake rates were measured for 47 derivatives of PrAMP Onc112 and compared to the minimal inhibitory concentrations (MIC) of each peptide. Ribosomal binding was evaluated for ribosome extracts from four Gram‐negative bacteria. Bacterial uptake was assessed by quantifying each peptide in the supernatants of bacterial cultures. Oncocin analogues with a higher net positive charge appeared to be more active, although their ribosome binding and uptake rates were not necessarily better than for Onc112. The data suggest a complex mode of action influenced by further factors improving or reducing the antibacterial activity, including diffusion through membranes, transport mechanism, secondary targets, off‐target binding, intracellular distribution, and membrane effects. Relying only on in vitro binding and uptake data may not be sufficient for the rational development of more active analogues.

(Re)Defining the Proline-Rich Antimicrobial Peptide Family and the Identification of Putative New Members

As we rapidly approach a post-antibiotic era in which multi-drug resistant bacteria are ever-pervasive, antimicrobial peptides (AMPs) represent a promising class of compounds to help address this global issue. AMPs are best-known for their membrane-disruptive mode of action leading to bacteria cell lysis and death. However, many AMPs are also known to be non-lytic and have intracellular modes of action. Proline-rich AMPs (PrAMPs) are one such class, that are generally membrane permeable and inhibit protein synthesis leading to a bactericidal outcome. PrAMPs are highly effective against Gram-negative bacteria and yet show very low toxicity against eukaryotic cells. Here, we review both the PrAMP family and the past and current definitions for this class of peptides. Computational analysis of known AMPs within the DRAMP database (http://dramp.cpu-bioinfor.org/) and assessment of their PrAMP-like properties have led us to develop a revised definition of the PrAMP class. As a result, we subsequently identified a number of unknown and unclassified peptides containing motifs of striking similarity to known PrAMP-based DnaK inhibitors and propose a series of new sequences for experimental evaluation and subsequent addition to the PrAMP family.

Characteristics of Microbial Communities of Pachygrontha antennata (Hemiptera: Pachygronthidae) in Relation to Habitat Variables

The microbial community interacts with the environment and the health and immune function of its host both directly and indirectly. However, very few studies about microbial communities have considered habitat and external environmental variables. This study examined environmental influences on the microbial community of Pachygrontha antennata, which is found in various habitats (e.g., urban, forested, and agricultural areas). The results demonstrated that the composition of the microbial community differed according to land use, while the bacterial diversity did not. In urban areas with high environmental heterogeneity, microbial community diversity tended to be high. Furthermore, bacteria in forests and agricultural areas (e.g., Paraburkholderia, Burkholderia) have been found to be highly correlated with habitat variables. Therefore, we suggest that habitat variables should be considered in future symbiotic studies.

Intracellular Antimicrobial Peptides Targeting the Protein Synthesis Machinery

While antimicrobial peptides (AMPs) are well-known for their disruptive effects on bacterial membranes, the mechanism of many intracellular AMPs is still being elucidated. In the recent years, it has been demonstrated that the subclass of proline-rich AMPs (PrAMPs) can pass through the bacterial membrane and kill bacteria by inhibiting protein synthesis. PrAMPs are a product of the innate immune system and are secreted in response to bacterial infection. So far PrAMPs have been identified in many arthropods, such as beetles, wasps, and flies, as well as some mammals, such as sheep, cows, and goats. PrAMPs show high potency against Gram-negative bacteria, while exhibiting low toxicity in eukaryotes, suggesting that they may represent a promising avenue for the development of future antimicrobial agents to combat the increase of multidrug-resistant bacterial pathogens. Structural and biochemical data have revealed the PrAMP binding sites on the ribosome as well as insight into their mechanisms of action. While the binding site of all so far investigated PrAMPs is situated within nascent polypeptide exit tunnel, the mechanism of action is distinct between class I and II PrAMPs. Specifically, class I PrAMPs, such as Bac7, Onc112, pyrrhocoricin, and metalnikowin, block the delivery of aa-tRNA by EF-Tu to the ribosomal A-site, whereas the class II PrAMPs, such as apidaecin 1b and Api137, act during translation termination and inhibit protein synthesis by trapping of release factors on the 70S ribosome following hydrolysis of the nascent polypeptide chain.

The activity of a mammalian proline-rich peptide against Gram-negative bacteria, including drug-resistant strains, relies on a nonmembranolytic mode of action

Background

A peptide of 2,733 Da named SP-E, previously isolated from pig saliva and already described for its antifungal activity and absence of toxicity against mammalian cells, is characterized by a high content of proline residues (70% of entire sequence), that confer structural features probably related to peptide activity.

Purpose

The aim of this study was to evaluate the activity of SP-E against Gram-negative bacteria, including drug-resistant clinical isolates.

Methods

SP-E and shorter fragments of the same peptide were tested in vitro against the selected bacteria by colony forming unit assays. Scanning electron microscopy and confocal microscopy were also applied. SP-E potential therapeutic activity was evaluated in vivo in a Galleria mellonella model of bacterial infection.

Results

SP-E proved to be active against the tested bacteria with EC₅₀ values in the micro-molar range. Though maintaining antibacterial properties, the shorter peptides showed lower activity in respect to the parental molecule. Kinetics of killing action and nonmembranolytic internalization within Escherichia coli and Pseudomonas aeruginosa cells strongly suggested a cytosolic mechanism of action involving one or more intracellular molecular targets. A single injection of SP-E exerted a therapeutic effect in G. mellonella larvae infected with P. aeruginosa.

Conclusion

The biological properties of SP-E strongly back this peptide as a new promising multitasking antimicrobial molecule.

The Dolphin Proline-Rich Antimicrobial Peptide Tur1A Inhibits Protein Synthesis by Targeting the Bacterial Ribosome

Proline-rich antimicrobial peptides (PrAMPs) internalize into susceptible bacteria using specific transporters and interfere with protein synthesis and folding. To date, mammalian PrAMPs have so far been identified only in artiodactyls. Since cetaceans are co-phyletic with artiodactyls, we mined the genome of the bottlenose dolphin Tursiops truncatus, leading to the identification of two PrAMPs, Tur1A and Tur1B. Tur1A, which is orthologous to the bovine PrAMP Bac7, is internalized into Escherichia coli, without damaging the membranes, using the inner membrane transporters SbmA and YjiL/MdM. Furthermore, like Bac7, Tur1A also inhibits bacterial protein synthesis by binding to the ribosome and blocking the transition from the initiation to the elongation phase. By contrast, Tur1B is a poor inhibitor of protein synthesis and may utilize another mechanism of action. An X-ray structure of Tur1A bound within the ribosomal exit tunnel provides a basis to develop these peptides as novel antimicrobial agents.

The Mechanisms of Action of Ribosome-Targeting Peptide Antibiotics

The ribosome is one of the major targets in the cell for clinically used antibiotics. However, the increase in multidrug resistant bacteria is rapidly reducing the effectiveness of our current arsenal of ribosome-targeting antibiotics, highlighting the need for the discovery of compounds with new scaffolds that bind to novel sites on the ribosome. One possible avenue for the development of new antimicrobial agents is by characterization and optimization of ribosome-targeting peptide antibiotics. Biochemical and structural data on ribosome-targeting peptide antibiotics illustrates the large diversity of scaffolds, binding interactions with the ribosome as well as mechanism of action to inhibit translation. The availability of high-resolution structures of ribosomes in complex with peptide antibiotics opens the way to structure-based design of these compounds as novel antimicrobial agents.

Differential stability of therapeutic peptides with different proteolytic cleavage sites in blood, plasma and serum

Proteolytic degradation of peptide-based drugs is often considered as major weakness limiting systemic therapeutic applications. Therefore, huge efforts are typically devoted to stabilize sequences against proteases present in serum or plasma, obtained as supernatants after complete blood coagulation or centrifugation of blood supplemented with anticoagulants, respectively. Plasma and serum are reproducibly obtained from animals and humans allowing consistent for clinical analyses and research applications. However, the spectrum of active or activated proteases appears to vary depending on the activation of proteases and cofactors during coagulation (serum) or inhibition of such enzymes by anticoagulants (plasma), such as EDTA (metallo- and Ca²⁺-dependent proteases) and heparin (e.g. thrombin, factor Xa). Here, we studied the presumed effects on peptide degradation by taking blood via cardiac puncture of CD-1 mice using a syringe containing a peptide solution. Due to absence of coagulation activators (e.g. glass surfaces and damaged cells), visible blood clotting was prevented allowing to study peptide degradation for one hour. The remaining peptide was quantified and the degradation products were identified using mass spectrometry. When the degradation rates (half-life times) were compared to serum derived freshly from the same animal and commercial serum and plasma samples, peptides of three different families showed indeed considerably different stabilities. Generally, peptides were faster degraded in serum than in plasma, but surprisingly all peptides were more stable in fresh blood and the order of degradation rates among the peptides varied among the six different incubation experiments. This indicates, that proteolytic degradation of peptide-based therapeutics may often be misleading stimulating efforts to stabilize peptides at degradation sites relevant only in vitro, i.e., for serum or plasma stability assays, but of lower importance in vivo.

Proline-rich antimicrobial peptides targeting protein synthesis

Proline-rich antimicrobial peptides (PrAMPs) bind within the exit tunnel of the ribosome and inhibit translation elongation. Structures of ribosome-bound PrAMPs reveal the interactions with ribosomal components and could pave the way for the development of novel peptide-based antimicrobial agents.

Readily adaptable release kinetics of prodrugs using protease-dependent reversible PEGylation

Protein and peptide therapeutics with good in vitro activities often fail due to poor bioavailability, circulation lifetime, and immunogenicity. PEGylation, i.e. conjugation of polyethylene glycol (PEG), significantly improves serum stability and renal clearance besides reducing the immunogenicity and thus enhances pharmacokinetics and tolerance in vivo. Several PEGylated drugs are marketed including several top-selling blockbusters. However, PEGylation can mask the binding site, especially in peptides, and thereby reduce the activity drastically, which is only rarely compensated by the improved bioavailability. Prodrug strategies using temporary PEGylation, i.e. the authentic drug is released from a PEG-linked precursor by hydrolysis or enzymatic degradation, can overcome these weaknesses. Recently, we reported a strategy coupling PEG via a peptide linker cleaved C-terminally by trypsin-like proteases in blood to release the unmasked therapeutic peptide. Here, we designed twelve short peptide linkers (four or five residues) to tune the release-rates of oncocin Onc112, a proline-rich antimicrobial peptide. In 25% aqueous mouse serum, Onc112 was released with half-life times from 0.5 to 12h. When elongated N-terminally with 5kDa ɑ-methoxy-ω-mercapto PEG as thioether, the half-life times of the prodrugs ranged from 7 to 42h in full mouse serum. Conjugation of a 20kDa instead of the 5kDa PEG increased the half-life times more than twofold, whereas longer peptide linkers up to twelve residues increased them only slightly. In all cases, Onc112 was released continuously providing stable peptide levels for at least 16h. The kinetics will allow the specific design of PEG-linker-drug-combinations for optimizing the pharmacokinetics of promising peptide therapeutics.

Immunogenicity and pharmacokinetics of short, proline-rich antimicrobial peptides

Aim: The potential of proline-rich antimicrobial peptides (PrAMPs) to treat multidrug-resistant Gram-negative pathogens has been intensively investigated. They are efficacious at low doses in infection models and well tolerated in healthy mice at high doses. Methods & results: PrAMPs Onc72 and Api88 were nonimmunogenic in mice unless conjugated to a carrier protein. Monoclonal IgG1/IgG2b antibodies produced by hybridoma cells were mapped to different Onc72 regions and combined in a sandwich-ELISA in a pharmacokinetic study. Onc72 was detected at concentrations up to 32 µg/ml in murine blood after administering 20 mg/kg and reached several organs within 10 min. Conclusion: Both PrAMPs were not immunogenic and Onc72 concentrations in blood were well above the minimal inhibitory concentrations for Enterobacteriaceae further confirming their potential as novel antibiotics.

Influence of the yjiL-mdtM Gene Cluster on the Antibacterial Activity of Proline-Rich Antimicrobial Peptides Overcoming Escherichia coli Resistance Induced by the Missing SbmA Transporter System

In view of increasing health threats from multiresistant pathogens, antimicrobial peptides (AMPs) and, specifically, proline-rich AMPs (PrAMPs) have been investigated in animal models. PrAMPs enter bacteria via the ABC transporter SbmA and inhibit intracellular targets. We used phage transduction (Tn10 insertion) to screen by random mutagenesis for alternative uptake mechanisms for analogs of apidaecin 1b, a honeybee-derived PrAMP. All 24 apidaecin-resistant mutants had the Tn10 insertion in the sbmA gene. These sbmA::Tn10 insertion mutants and the Escherichia coli BW25113 ΔsbmA (JW0368) strain were still susceptible to the bactenecin PrAMP Bac7(1-35) and oncocin PrAMPs Onc18 and Onc112, as well as to Chex1-Arg20, despite significantly reduced internalizations. In a second round of random mutagenesis, the remaining susceptibility was linked to the yjiL-mdtM gene cluster. E. coli BW25113 and its ΔyjiL null mutant (JW5785) were equally susceptible to all PrAMPs tested, whereas the BW25113 ΔmdtM mutant was less susceptible to oncocins. The JW0368 yjiL::Tn10 transposon mutant (BS2) was resistant to all short PrAMPs and susceptible only to full-length Bac7 and A3-APO. Interestingly, PrAMPs appear to enter bacteria via MdtM, a multidrug resistance transporter (drug/H(+) antiporter) of the major facilitator superfamily (MFS) that can efflux antibiotics, biocides, and bile salts. In conclusion, PrAMPs enter bacteria via ABC and MFS transporters that efflux antibiotics and cytotoxic compounds from the cytoplasm to the periplasm.

Peptides and Peptidomimetics for Antimicrobial Drug Design

The purpose of this paper is to introduce and highlight a few classes of traditional antimicrobial peptides with a focus on structure-activity relationship studies. After first dissecting the important physiochemical properties that influence the antimicrobial and toxic properties of antimicrobial peptides, the contributions of individual amino acids with respect to the peptides antibacterial properties are presented. A brief discussion of the mechanisms of action of different antimicrobials as well as the development of bacterial resistance towards antimicrobial peptides follows. Finally, current efforts on novel design strategies and peptidomimetics are introduced to illustrate the importance of antimicrobial peptide research in the development of future antibiotics.

The proline-rich antimicrobial peptide Onc112 inhibits translation by blocking and destabilizing the initiation complex

The increasing prevalence of multidrug-resistant pathogenic bacteria is making current antibiotics obsolete. Proline-rich antimicrobial peptides (PrAMPs) display potent activity against Gram-negative bacteria and thus represent an avenue for antibiotic development. PrAMPs from the oncocin family interact with the ribosome to inhibit translation, but their mode of action has remained unclear. Here we have determined a structure of the Onc112 peptide in complex with the Thermus thermophilus 70S ribosome at a resolution of 3.1 Å by X-ray crystallography. The Onc112 peptide binds within the ribosomal exit tunnel and extends toward the peptidyl transferase center, where it overlaps with the binding site for an aminoacyl-tRNA. We show biochemically that the binding of Onc112 blocks and destabilizes the initiation complex, thus preventing entry into the elongation phase. Our findings provide a basis for the future development of this class of potent antimicrobial agents.

Evidence that a laminin-like insect protein mediates early events in the interaction of a Phytoparasite with its vector's salivary gland

Phytomonas species are plant parasites of the family Trypanosomatidae, which are transmitted by phytophagous insects. Some Phytomonas species cause major agricultural damages. The hemipteran Oncopeltus fasciatus is natural and experimental host for several species of trypanosomatids, including Phytomonas spp. The invasion of the insect vectors' salivary glands is one of the most important events for the life cycle of Phytomonas species. In the present study, we show the binding of Phytomonas serpens at the external face of O. fasciatus salivary glands by means of scanning electron microscopy and the in vitro interaction of living parasites with total proteins from the salivary glands in ligand blotting assays. This binding occurs primarily through an interaction with a 130 kDa salivary gland protein. The mass spectrometry of the trypsin-digest of this protein matched 23% of human laminin-5 β3 chain precursor sequence by 16 digested peptides. A protein sequence search through the transcriptome of O. fasciatus embryo showed a partial sequence with 51% similarity to human laminin β3 subunit. Anti-human laminin-5 β3 chain polyclonal antibodies recognized the 130 kDa protein by immunoblotting. The association of parasites with the salivary glands was strongly inhibited by human laminin-5, by the purified 130 kDa insect protein, and by polyclonal antibodies raised against the human laminin-5 β3 chain. This is the first report demonstrating that a laminin-like molecule from the salivary gland of O. fasciatus acts as a receptor for Phytomonas binding. The results presented in this investigation are important findings that will support further studies that aim at developing new approaches to prevent the transmission of Phytomonas species from insects to plants and vice-versa.

Oncocin derivative Onc72 is highly active against Escherichia coli in a systemic septicaemia infection mouse model

OBJECTIVES

The antimicrobial oncocin derivative Onc72 is highly active against a number of Gram-negative bacteria, including resistant strains. Here we study its toxicity and efficacy in a lethal mouse infection model.

METHODS

In an acute toxicity study, purified Onc72 was administered to NMRI mice in four consecutive injections within a period of 24 h as an intraperitoneal bolus. The animals' behaviour was monitored for 5 days, before several organs were examined by histopathology. A lethal Escherichia coli infection model was established and the efficacy of Onc72 was evaluated for different peptide doses considering the survival rates of each dose group and the bacterial counts in blood, lavage and organs.

RESULTS

Intraperitoneal bolus injections with single doses of 20 or 40 mg of Onc72 per kg of body weight did not result in any abnormal animal behaviour. No mouse became moribund or died within the studied period. Histopathological examinations revealed no toxic effects. When infected with E. coli at a lethal dose, none of the untreated animals survived the next 24 h, whereas all animals treated three times with Onc72 at doses of ≥5 mg/kg survived the observation period of 5 days. No bacteria were detected in the blood of treated animals after day 5 post-infection. The effective dose (ED(50)) was ∼2 mg/kg.

CONCLUSIONS

No toxic effects were observed for Onc72 within the studied dose range up to 40 mg/kg, indicating a safety margin of >20.

Proline-rich antimicrobial peptides: converging to a non-lytic mechanism of action

Proline-rich antimicrobial peptides are a group of cationic host defense peptides of vertebrates and invertebrates characterized by a high content of proline residues, often associated with arginine residues in repeated motifs. Those isolated from some mammalian and insect species, although not evolutionarily related, use a similar mechanism to selectively kill Gram-negative bacteria, with a low toxicity to animals. Unlike other types of antimicrobial peptides, their mode of action does not involve the lysis of bacterial membranes but entails penetration into susceptible cells, where they then act intracellularly. Some aspects of the transport system and cytoplasmic targets have been elucidated. These features make them attractive both as anti-infective lead compounds and as a new class of potential cell-penetrating peptides capable of internalising membrane-impermeant drugs into both bacterial and eukaryotic cells.

Bactericidal oncocin derivatives with superior serum stabilities

The proline-rich antimicrobial peptide oncocin is remarkably active in vitro against a number of important Gram-negative bacteria of concern to humans owing to their increasing resistance to antibiotics, i.e. Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae) and non-fermenting species (Acinetobacter baumannii and Pseudomonas aeruginosa). Degradation of oncocin in mouse serum was investigated in this study. Several approaches to stabilise the main cleavage sites (C-terminal to Arg-15 and N-terminal to Arg-19) by substituting either or both arginine (Arg) residues with non-proteinogenic amino acids, i.e. α-amino-3-guanidino-propionic acid, homoarginine, nitro-arginine, N-methyl-arginine, β-homoarginine, D-arginine (D-Arg) or ornithine (Orn), were tested. These modifications were found to increase the half-life of oncocin in full mouse serum. For oncocin with two Orn residues in positions 15 and 19, the half-life in full serum increased from 25 min to 3 h. An increase of >8 h was observed for oncocin with two D-Arg residues at these same positions. The antibacterial activities of these modified sequences were slightly better than the original oncocin sequence. Moreover, the three most stable analogues were found to be bactericidal against E. coli and were not toxic to HeLa cells or haemolytic to human erythrocytes.

Up-regulation of lipophorin (Lp) and lipophorin receptor (LpR) gene in the mosquito, Culex quinquefasciatus (Diptera: Culicidae), infected with the filarial parasite, Wuchereria bancrofti (Spirurida: Onchocercidae)

In mosquitoes, including Culex quinquefasciatus, immune molecules are known to be upregulated or produced de novo upon exposure to parasites or pathogens. These molecules are regulatory in nature acting against parasite or pathogen infection and development. Similarly, there are molecules that are upregulated to facilitate parasite development in the vector mosquitoes. Lipophorin, a major lipid transporting lipoprotein in the hemolymph of insects, is implicated as a helper molecule in the clotting mechanism and facilitator of parasite and pathogen development in mosquitoes. In the present study, upregulation of a 240 kDa protein was detected in C. quinquefasciatus infected with the human lymphatic filarial parasite, Wuchereria bancrofti. It was identified as a lipophorin through nano-Lc-MS/MS analysis. Transcription of the lipophorin receptor gene also was identified through RACE-PCR. C. quinquefasciatus is the vector of W. bancrofti, and it allows successful development of the parasite. The role of upregulated lipophorin and transcription of its receptor gene in this mosquito could be implicated as a facilitator for the parasite development.

Influence of Pseudomonas putida AF7 inoculation on soil enzymes

There has been some concern about the environmental impact of microbial agents. Pseudomonas may be used as bioremediator and as biopesticide. In this study, we report the use of soil enzyme assays as biological indicator of possible negative effects in soil functioning after the P. putida AF7 inoculation. For that, P. putida AF7 was originally isolated from the rizosphere of rice and was inoculated on three soil types: Rhodic Hapludox (RH), Typic Hapludox (TH); and Arenic Hapludult (AH). The acid phosphatase, beta-glucosidase and protease enzymes activities were measured for three period of evaluation (7, 14 and 21 days). In general, the enzymatic activities presented variation among the tested soils. The highest activities of beta-glucosidase and acid phosphatase were observed in the RH and AH soils, while the protease activity was higher in the TH soil. Also, the soil characteristics were measured for each plot. The activity of enzymes from the carbon cycle was positively correlated with the N and the P and the enzyme from the nitrogen cycle was negatively correlated with N and C.org. The presented data indicate that soil biochemical properties can be an useful tool for use as an indicator of soil perturbations by microbial inoculation in a risk assessment.

Assessing the safety of Pseudomonas putida introduction in the environment: an overview of ecotoxicological tests

Risk assessment guidelines for the environmental release of microbial agents are performed in a tiered sequence which includes evaluation of exposure effects on non-target organisms. However, it becomes important to verify whether environmental risk assessment from temperate studies is applicable to tropical countries, as Brazil. Pseudomonas putida is a bacteria showing potential to be used for environmental applications as bioremediation and plant disease control. This study investigates the effects of this bacteria exposure on rodents and aquatic organisms (Daphnia similis) that are recommended to be used as non-target organism in environmental risk assessments. Also, the microbial activity in three different soils under P. putida exposure was evaluated. Rats did not show clinical alterations, although the agent was recovered 16h after the exposure in lung homogenates. The bacteria did not reduce significantly the reproduction and survival of D. similis. The soil enzymatic activities presented fluctuating values after inoculation with bacteria. The measurement of perturbations in soil biochemical characteristics is presented as an alternative way of monitoring the overall effects of the microbial agent to be introduced even in first stage (Tier I) of the risk assessment in tropical ecosystems.

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

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

Actin protein up-regulated upon infection and development of the filarial parasite, Wuchereria bancrofti (Spirurida: Onchocercidae), in the vector mosquito, Culex quinquefasciatus (Diptera: Culicidae)

Detection and identification of humoral proteins, which are up-regulated in Culex quinquefasciatus upon infection by Wuchereria bancrofti, is important in tracing out the biochemical consequences of the filarial parasite development in the vector mosquito. Analysis of the haemolymph of infected mosquitoes through SDS-PAGE and RP-HPLC showed up-regulation of five proteins of molecular weights 40, 66, 22, 14, and 7-kDa. Among these, only the 40-kDa was unknown and the others were comparable with those already reported as transferrin, attacin, lysozyme, and defensin, respectively. In the present study, the 40-kDa protein up-regulated upon infection was identified as actin through nano-LC-MS/MS analysis. Actin is known to be one of the cytoskeletal proteins up-regulated in the haemolymph, as part of the innate immune system, of Escherichia coli challenged Drosophila melanogaster larvae. For the first time, we have observed an increased level of actin in the haemolymph of W. bancrofti-infected Cx. quinquefasciatus. However, the exact mechanism of actin involvement in the immune system of this mosquito is yet to be studied.