Otto Schmidt

University of Adelaide, Tarndarnya, South Australia, Australia

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Publications (92)284.7 Total impact

  • Gang Ma · Otto Schmidt · Mike Keller
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    ABSTRACT: Crystal toxins from Bacillus thuringiensis bind to glycolipids and glycoproteins using two different lectin domains in the toxin protein. Our previous observations suggested that the sequestration of crystal toxin depends on the functional interaction of a toxin lectin with glycolipids. Given the finding that competition of a galectin LEC-8 with Cry5B for binding to glycolipids resulting in reduced Bt toxicity in nematode, it is interesting to explore the role of LEC-8 in insects. Here, we reported that the LEC-8 can also be exploited by insect for their survival when they were fed with Bt toxin food. Bioassay with LEC-8 showed that pre-feeding of Helicoverpa armigera larvae reduced the Cry1Ac susceptibility. Both LEC-8 and Cry1Ac bind to the midgut glycolipid in a similar way. Further ELISA indicated that LEC-8 interacts with glycolipid from insect midgut, thus reduce Cry1Ac binding to glycolipid. This in turn enhances insect tolerance to Cry1Ac toxin. The sugar determinants of LEC-8 were studied by using haemagglutination (HA) and haemagglutination inhibition (HAI) assay. It was suggested that the terminal sugar of LEC-8 has multiple sugar binding property.
    No preview · Article · Dec 2012 · Results in Immunology
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    ABSTRACT: Analysing food webs in agricultural habitats is essential for the development of natural control strategies. Several molecular tools to investigate trophic interactions on a species-specific level have been developed in recent years and their advantages and limitations have been discussed. With this study we introduce another tool, terminal restriction fragment length polymorphism (tRFLP). Generalist predators found in Australian brassica crops, their prey and abundant parasitoids were chosen as a model system to adapt and evaluate the tRFLP approach. Using general primers and selecting six restriction enzymes, we obtained species-specific tRF patterns for 21 of the most abundant arthropods in brassica crops. We detected up to three prey species in the gut contents of laboratory-fed predators. Detection rates differed among predators, ranging between 28 and 100%. The identification of a species-specific tRF pattern was strongly affected by the presence and concentrations of DNA from other species. In a preliminary field study, prey could be identified from 20% of the collected brown lacewings. The advantage of the tRFLP method is the possibility of identifying multiple species at once. This advantage is counterbalanced by methodological limitations, among which the most critical one is the fact that it will be difficult to maintain specificity in highly diverse ecosystems. However, if species diversity is limited and the target sequence and the primers are chosen to increase detection success, the tRFLP method can be used to study trophic interactions in the field.
    Full-text · Article · Mar 2012
  • Ma G · Schmidt O · Keller M

    No preview · Article · Feb 2012

  • No preview · Article · Jan 2012

  • No preview · Article · Jan 2012 · Developmental & Comparative Immunology
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    ABSTRACT: Endotoxins from the soil bacterium Bacillus thuringiensis are used worldwide to control insect pests and vectors of diseases. Despite extensive use of the toxins as sprays and in transgenic crops, their mode of action is still not completely known. Here we show that two crystal toxins binding to different glycoprotein receptors have similar glycolipid binding properties. The glycolipid binding domain was identified in a recombinant peptide representing the domain II of the crystal toxin Cry1Ac (M-peptide). The recombinant M-peptide was isolated from bacterial lysates as a mixture of monomers and dimers and formed tetramers upon binding to glycolipid microvesicles from gut tissues and lipid particles from hemolymph plasma. Likewise, when mature toxins and M-peptides where mixed with plasma, these peptides bind to lipid particles and can be separated with lipophorin particles on low-density gradients. When mature toxin and M-peptides are added to lipid particles in increasing amounts, the peptide-particle complexes form higher aggregates that are similar to aggregates formed in low-density gradients in the presence of the toxin. This could indicate that glycolipids on lipid particles are possible targets for toxin monomers in the gut lumen, which upon binding to the glycolipids form tetramers and aggregate particles and thereby sequester the toxin inside the gut lumen before it can interact with receptors on the brush border membrane. The implication is that domain II interacting with glycolipids mediate tolerance to the toxin that is separate from interaction of the toxin with glycoprotein receptors causing toxicity.
    No preview · Article · Sep 2011 · Developmental and comparative immunology
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    Y.A. Batta · M. Rahman · K. Powis · G. Baker · O. Schmidt
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    ABSTRACT: Aims: To isolate and formulate a native strain of Zoophthora radicans naturally infecting larvae of diamondback moth, Plutella xylostella, existing in South Australia and to provide evidence that formulation of the fungus is effective against P. xylostella larvae, and therefore, it could be used as a tool in pest management of this insect. Methods and Results: Dose–response bioassays using formulated and unformulated forms of the fungus strain were carried out against third instar larvae of P. xylostella. Results obtained have indicated a significant increase in the larval mortality when higher concentrations of a formulated form of the fungus strain were applied compared to the treatments with the unformulated form (85·0 vs 57·5% of larval mortality, respectively, at the top concentration of 107 conidia/ml). The median lethal concentration (LC50) for a formulated form was 100 times less than that of the unformulated form when they were applied against the third instar larvae of P. xylostella. In addition, the formulation used in the present bioassays has preserved the viability of introduced fungus conidia for longer time in comparison with the unformulated conidia. Conclusions: The effective application of a formulated fungus strain against P. xylostella larvae constitutes the first step towards its use in pest management of this insect. Significance and Impact of the Study: The formulated fungus in inverted emulsion could be used as an alternative tool to insecticides in pest management of P. xylostella larvae because of the development of resistance to insecticides in the treated larvae.
    Full-text · Article · Feb 2011 · Journal of Applied Microbiology
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    Mahbub Rahman · Richard Glatz · Rick Roush · Otto Schmidt
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    ABSTRACT: Exposure of insect larvae to sublethal concentrations of crystal toxins from the soil bacterium Bacillus thuringiensis (Bt toxins) causes the induction of immune and metabolic responses that can be transmitted to offspring by epigenetic inheritance mechanisms. Given that the elevated immune status carries significant developmental penalties, we wanted to establish the relationships between immune induction, tolerance to the toxin and developmental penalties. A laboratory culture of Helicoverpa armigera was induced by a sublethal bacterial suspension containing crystal toxin Cry1Ac in one generation and maintained in the presence of toxin, acquiring significant levels of tolerance to the toxin within 12 generations of continuous exposure. Comparing tolerant and susceptible insects, we show that the induction of larval immune response and the coincident alteration of development-related metabolic activities by elicitors in the larval gut (larval induction) differs from the elevated immune status transmitted by epigenetic mechanisms (embryonic induction). Because the damaging effects of larval induction processes are higher compared to embryonic induction, it is likely that overall developmental penalties depend on the relative contribution of the two induction processes. When insects are kept with the same amount of toxin in the diet for subsequent generations, the embryonic induction process increases its contribution compared to the larval induction, resulting in reduced overall developmental penalty, while tolerance to the toxin is maintained.
    Full-text · Article · Feb 2011 · Applied and Environmental Microbiology
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    ABSTRACT: Bacterial infections represent a serious health care problem, and all multicellular organisms have developed defense mechanisms to eliminate pathogens that enter the host via different paths including wounds. Many invertebrates have an open circulatory system, and effective coagulation systems are in place to ensure fast and efficient closure of wounds. It was proposed early on that coagulation systems in invertebrates play a major role not only in sealing wounds but also in preventing systemic infections. More recent evidence suggests that vertebrates, too, rely on clotting as an immune effector mechanism. Here we discuss the evolution of clotting systems against the background of their versatile function in innate immunity.
    No preview · Article · Nov 2010 · Journal of Innate Immunity
  • M M Rahman · G Baker · K J Powis · R T Roush · O Schmidt
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    ABSTRACT: Field surveys of pest insect pest populations in agroecosystems reveal low but significant levels of tolerance to synthetic and biological pesticides but fail to uncover resistance alleles in test crosses. To study the potential of inducible mechanisms to generate tolerance to synthetic pesticides, we performed baseline susceptibility studies in field and laboratory populations of diamondback moth, Plutella xylostella (L.), to commercial formulations of emamectin benzoate. Pesticide exposure in the field caused elevated levels of tolerance, which decreased in field-collected populations after maintaining insects with pesticide-free diet in the laboratory. Because no significant resistance alleles were identified in back-crossed individuals, the observed increase in tolerance was probably not based on preexisting recessive resistance mechanisms in the population. Instead, the genetic analysis after five and 12 generations is compatible with a transient up-regulation of an immune and metabolic status in tolerant insects that can be transmitted to offspring by a maternal effect. Although the epigenetic effects contributed to incremental increases in tolerance in the first five generations, other resistance mechanisms that are transmitted genetically predominate after 12 generations of increased exposure to the pesticide.
    No preview · Article · Aug 2010 · Journal of Economic Entomology
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    ABSTRACT: The recognition and inactivation of toxins and pathogens are mediated by a combination of cell-free and cellular mechanisms. A number of soluble and membrane-bound pattern recognition molecules interact with elicitors to become involved in both cell-free inactivation as well as cellular uptake reactions. Here we describe the possible recognition and effector function of key arthropod immune proteins, such as peroxinectin, hemolin, and hemomucin, as an outcome of changes in adhesiveness, which drive self-assembly reactions leading to cell-free coagulation and cellular uptake reactions. The fact that some of these proteins are essential for immune and developmental functions in some species, but are not found in closely related species, may point to the existence of multiprotein assemblies, which are conserved at the mechanistic level and can function with more than one combination of protein constituents.
    No preview · Article · Oct 2009 · Annual Review of Entomology
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    ABSTRACT: While arsenic is toxic to all multicellular organisms, some organisms become tolerant by an unknown mechanism. We have recently uncovered an inducible tolerance mechanism in insects, which is based on a sequestration of toxins and pathogens by lipid particles. To examine whether arsenic interacts with lipid particles from mammals we compared binding of arsenic to lipid particles from insect and pig plasma after separation of lipid particles by low-density gradient centrifugation. Arsenic was found in both organisms in an area of the gradient, which corresponds to lipid-rich lipid particles. Since iron is known to affect arsenic toxicity in some organisms, we asked whether iron may be present in lipid particles. When low density cell (LDC) gradient fractions were analysed for the presence of iron we detected a peak in very low-density fractions similar to those that carried arsenic. This could indicate that arsenic interacts with lipid particles that contain iron and, if arsenic is removed from the plasma by lipid particles, that would also reduce iron-containing lipid particles at the time of arsenic emergence in the plasma. To test this assumption we measured the iron content in plasma at various time periods after the toxin ingestion. This time course revealed that iron is depleted in plasma fractions when arsenic shows a peak. Our data suggest that arsenic interacts with invertebrate and vertebrate lipid particles that are associated with proteins that may lead to detoxification by cell-free or cellular sequestration mechanisms.
    No preview · Article · Apr 2009 · Environmental Geochemistry and Health
  • M M Sohani · P M Schenk · C J Schultz · O Schmidt
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    ABSTRACT: Protein domains with similarity to plant strictosidine synthase-like (SSL) sequences have been uncovered in the genomes of all multicellular organisms sequenced so far and are known to play a role in animal immune responses. Among several distinct groups of Arabidopsis thaliana SSL sequences, four genes (AtSSL4-AtSSL7) arranged in tandem on chromosome 3 show more similarity to SSL genes from Drosophila melanogaster and Caenorhabditis elegans than to other Arabidopsis SSL genes. To examine whether any of the four AtSSL genes are immune-inducible, we analysed the expression of each of the four AtSSL genes after exposure to microbial pathogens, wounding and plant defence elicitors using real-time quantitative RT-PCR, Northern blot hybridisation and Western blot analysis with antibodies raised against recombinant AtSSL proteins. While the AtSSL4 gene was constitutively expressed and not significantly induced by any treatment, the other three AtSSL genes were induced to various degrees by plant defence signalling compounds, such as salicylic acid, methyl jasmonate and ethylene, as well as by wounding and exposure to the plant pathogens Alternaria brassicicola and cucumber mosaic virus. Our data demonstrate that the four SSL-coding genes are regulated individually, suggesting specific roles in basal (SSL4) and inducible (SSL5-7) plant defence mechanisms.
    No preview · Article · Feb 2009 · Plant Biology

  • No preview · Article · Jan 2009
  • Muhammad Sarjan · Gang Ma · Mahbubur Rahman · Otto Schmidt

    No preview · Article · Jan 2009
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    ABSTRACT: Monoterpenoid indole alkaloids (MIA) are a diverse class of secondary metabolites important for plant protection and are drugs for treating human diseases. Arabidopsis thaliana (L.) is not known to produce MIAs, yet its genome has 15 genes with similarity to the periwinkle (Catharanthus roseus (L.) G. Don) strictosidine synthase (STR) gene. Phylogenetic analysis of strictosidine synthase-like (SSL) proteins reveals four well supported classes of SSLs in Arabidopsis. To determine if Arabidopsis produces active strictosidine synthase, Arabidopsis protein extracts were assayed for enzymatic activity and cDNAs were expressed in Escherichia coli. Arabidopsis protein extracts from leaves and hairy roots do not make strictosidine at levels comparable to C. roseus, but they metabolise one substrate, secologanin, a precursor of strictosidine in other plant species, and produce an 'unknown' compound proposed to be a dimer of secologanic acid. Recombinant Arabidopsis proteins expressed in E. coli were not active STRs. Quantitative PCR analysis was performed on class A Ssls and showed they are upregulated by salt, ultraviolet light and salicylic acid treatment. RNAi mutants of Arabidopsis with reduced expression of all four class A Ssls, suggest that class A SSL proteins can modify secologanin. Gene expression and metabolomics data suggests that class A Ssl genes may have a role in plant protection.
    No preview · Article · Jan 2009 · Functional Plant Biology
  • Otto Schmidt · Ulrich Theopold · Nancy E. Beckage
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    ABSTRACT: This chapter uses a comparison between insect and higher vertebrate immune reactions to highlight some of the progress that has been made in the understanding of how innate immune recognition has evolved to protect multicellular organisms against potentially damaging organisms. The similarities between mammals and nonmammals are more than one that is reflected in their sensing mechanisms, which affects recognition of pathogen-associated molecular structures. The binding properties of antibodies, enabling the variable binding domains to attach to almost any molecular structure (antigens) and the ontogenic elimination process of self-binding antibodies by clonal selection, allow higher vertebrates with adaptive immune systems to signal nonself structures. The similarities are also evident in extracellular sensor particles, recognition of self, and recognition of altered-self. The differences between insect and vertebrate immunity are evident in acquired (adaptive) immune system in higher vertebrates and immunological memory, involving clonally selected antibody-producing cells and inducible tolerance and memory in invertebrates. One of the questions associated with immune induction and protection is the size of the fitness cost imposed on the insect, which is difficult to explain by the induction of immune proteins alone. However, the recent observation that lipid particles are procoagulants and involved in defense and detoxification reactions could indicate immune-related post-translational modifications of lipid particles that affect lipid transport and metabolism. The most unexpected outcome of experimental studies involving the induction of the immune defense is that the elevated immune status can be transmitted to subsequent generations. Whatever the mechanism, the implications are that insects are able to acquire tolerance to damaging objects or substances by an incremental increase of an induced immune status in subsequent generations.
    No preview · Chapter · Dec 2008
  • Reza Hosseini · Otto Schmidt · Michael A. Keller
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    ABSTRACT: This study aimed to determine factors that influence the detection of DNA of Plutella xylostella L. (Lepidoptera: Plutellidae) in the gut contents of arthropod predators when the polymerase chain reaction is used to amplify a diagnostic fragment of the gene coding for cytochrome oxidase subunit I. The effects of temperature, time since feeding, subsequent food intake, sex, weight, and species of predator on prey detectability were studied in the laboratory. Three types of predator were studied: the spider Venator spenceri Hogg. (Araneae: Lycosidae), a bug with sucking mouthparts, Nabis kinbergii (Reuter) (Heteroptera: Nabidae), and a coccinellid with chewing mouthparts, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae). In all experiments, the detectability of prey DNA was negatively correlated with time post-feeding. The duration of detectability differed among the predator species. The time calculated for median detection success at 20 °C ranged from 49.6 h in V. spenceri to 36.1 h in N. kinbergii and 17.1 h in H. variegata. In H. variegata, but not in V. spenceri, the rate of detection decreased with increasing temperature. Subsequent food intake did not affect the detectability of DNA of P. xylostella in V. spenceri. In H. variegata, sex and weight of the predator did not influence detection of prey DNA. In addition, this study uncovered potential sources of error caused by detection of prey DNA following secondary cannibalistic and intraguild predation. The results provide essential information for the interpretation of prey detection data from field-collected predators’ gut contents.
    No preview · Article · Feb 2008 · Entomologia Experimentalis et Applicata
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    ABSTRACT: Tolerance to Bacillus thuringiensis crystal endotoxins (Bt-toxins) is correlated with an elevated immune status in larvae of the flour moth Ephestia kuehniella. To gain more specific information about the effector pathways involved in the protection against the toxin, we studied the effects of Bt-toxin formulations in susceptible (non-induced) and tolerant (immune-induced) larvae after natural (parasitism-mediated) and chemical (tropolone-mediated) suppression of defence reactions. Although melanization in hemolymph was significantly reduced, there was no significant effect on susceptibility to the toxin in parasitised or tropolone-treated larvae. This suggests that melanization of hemolymph is correlated with an elevated immune status but not responsible for the observed tolerance to Bt-toxin. To examine whether hemolymph proteins exist in the gut lumen and function as pro-coagulants, we compared gut and plasma proteins of immune-induced with those of non-induced larvae. Here we show that the lipid carrier lipophorin represents a major component in the gut lumen and interacts with mature Bt-toxin to form a complex.
    Full-text · Article · Nov 2007 · Journal of Invertebrate Pathology
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    D Li · N Schellhorn · O Schmidt
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    ABSTRACT: Diamondback moth (DBM), Plutella xylostella, is known for causing damage to Brassica crops and developing resistance to chemical and biological pesticides; it has become one of the most difficult pests to manage in many regions around the world. The only way to reduce reliance on pesticides is to maximize the role of natural control agents for integrated pest management programs and be able to incorporate the mortality from control agents into pest control decision-making. More than 90 hymenopterous parasitoids are associated with DBM worldwide; among them, Diadegma semiclausum, is a major endoparasitoid of P. xylostella. To optimize parasitism of pests in pest control decision-making, it is necessary to develop rapid and simple methods for distinguishing parasitized from non-parasitized larvae in the field. Here we report on a number of diagnostic tools to identify parasitized larvae. One is based on differential melanization reactions in hemolymph due to immune suppression in parasitized larvae. The lack of coagulation reactions in hemolymph provides a simple initial test, where squashing a non-parasitized larva onto nitrocellulose membrane traps chlorophyll-containing gut content on the membrane leaving a green dot of clotted gut material. However, in immune-suppressed parasitized larvae, the gut content was washed away in absence of coagulation reactions and the membrane lacks a green dot. This tool alone or combined with others, allows quick detection of parasitized caterpillars in the field. We further showed that the antibody MAb 9A5 can be used to detect D. semiclausum parasitized larvae of DBM in Western blots.
    Full-text · Article · Sep 2007 · Bulletin of Entomological Research

Publication Stats

3k Citations
284.70 Total Impact Points


  • 1996-2012
    • University of Adelaide
      • School of Agriculture, Food and Wine
      Tarndarnya, South Australia, Australia
  • 2011
    • South Australian Research and Development Institute
      Tarndarnya, South Australia, Australia
  • 1993-1994
    • Stockholm University
      • Molecular Cell Biology Group
      Tukholma, Stockholm, Sweden
  • 1991
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany