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Toxaemic action of entomopathogenic nematode bacterium complexes
1660
Reports
and Abstracts
The marine invertebrates consist of several phylla ranging from the simplest pluricellular animals such as the sponges to animals such as the Cephalopods which have complete circulation and nervous systems. Many toxic species are to be found amongst this uniquely diversified group of organisms. The toxins involved may be divided into two groups according to the structural type to which they belong: varyingly complex organic molecules and proteinaceous compounds. In this presentation only the first group of toxic substances will be taken into consideration. The great number of bioactive secondary metabolites that have been isolated from the tissues of marine invertebrates are most often assumed to have a defensive function (predator deterrence, prevention of fouling, territorial competition, etc.) There exists a strong correlation between the absence of obvious physical defence mechanisms of an organism and the presence of unusual chemistry in its tissues. It is thus not surprising that the richest sources of these compounds have been sessile or slow-moving soft-bodied sponges, cnidarians, sea slugs, bryozoans and tunicates, while mobile (e.g. squid) and armoured species (e.g. crustaceans, snails) generally lack toxic secondary metabolites. The spectrum of compound types to be found in marine invertebrates is particularly impressive and can only be compared to the complexity of their structures. A survey of the different types of compounds occurring in the different classes of marine invertebrates will be made. Toxaemic action of entomopathogenic nematode bacterium complexes. N. Boemare, A. Givaudan, B. Duvic and M. Brehelin (Laboratoire de Pathologie Comparee, INRA-CNRS URA no. 2209, Universite Montpellier II, CP 101, 34095 Montpellier cedex 5, France). The broad host range of the entomopathogenic nematodes Steinernema and Heterorhabditis, against several insect species, is the result of efficient pathogenic actions developed by the nematodes and their symbiotic bacteria, Xenorhabdus and Photorhabdus, respectively. Pathogenicity is frequently the result of a low insect immunity against these agents and of several weapons produced by these complexes. There exist quite frequent features of non-recognition by the insect targets. Nematodes produce several weapons, such as helminthic toxins and an immune depressive factor, and above all the vector role of nematodes which inoculate their entomopathogenic symbionts into the body cavity of insects. Many Xenorhabdus species, except X. poinarii, and many Photorhabdus were found to be pathogenic by inoculation. Exotoxins have recently been characterized for X. nematophilus and P. luminescens. Xenorhabdus exotoxin was efficient against several Lepidoptera by inoculation of few nanograms of the purified product. This toxaemic action seems to be the initial cause of mortality, especially for particular insect species which are normally resistant to bacteria. The lethal process ended in a general septicaemia. Pathogenicity of the bacteria was also due to the contribution of exoenzymatic activities (proteases, lipases, phospholipases and hemolysins). In many cases, it was quite obvious that both partners co-operate to kill the insect host. With axenic S. glaseri, or its sole symbiont X. poinarii, no entomopathogenic action was recorded, but when both partners were re-associated the entomopathogenic action was restored. The significance of interactions between these aggressive elements depends on both the insect target and the bacterial-helminthic species. Insect-selective scorpion toxins contractive and flaccid : one or two modes of action) M. Stankiewicz,’ Khalifa* and M. Pelhate’ (IInstitute of Biology and Environment Protection, N. Copernicus University, Poland; and 2Laboratory of Neurophysiology, CNRS ER 120, Angers, France).
R. Ben Torun,
The effects of different toxins obtained from Buthinae scorpion venoms on Na+ conductance in insect neuronal membrane have been studied. Experiments were performed using the double oil-gap or the patch-clamp technique in current- and voltage-clamp conditions, on isolated giant axon or DUM neurons of a cockroach, Periplaneta americana. Scorpion venom contains toxins affecting Na+ conductance in neurons: cc-toxins slow inactivation of Nat channels, while /?-toxins shift the voltage dependence of Na+ channel activation to more negative potentials. The classification into n- and B-groups has been established after studies on vertebrate preparations, Our studies, together with the study performed by biochemists, indicate that scorpion venom also comprises cc-insect toxins. Other insect toxins, contractive and flaccid (according to the nomenclature of Zlotkin et al.), have an opposite global effect on intact insects. However, both groups may primarily modify the voltage dependence and the kinetics of Na+ current activation in insects, as b-toxins do in vertebrates. It is proposed to classify both the groups as /I-like insect toxins. A better characterization of one or several /I-site(s) in insect Na+ channels is essential. Nevertheless, apparent opposite global poisoning effects would be due to quantitative rather than qualitative differences in the toxin-channel interactions.
PRESENTATIONS The abstracts
are listed alphabetically
by presenting
author
Importance of the fourth disuljide bridge in the maurotoxin structure and activity. R. Ben Khalifa,‘,’ M. Crest, M. Pelhate,’ R. Kharrat,? H. Darbon,4 M. El Ayeb,? J. Van Rietshotens H. Rochati and J.-M. SabatierS (‘Laboratory of Neurophysiology, CNRS ER120, Angers University, France; 2Laboratory of Neurobiology, CNRS UPR 9024, Marseille, France; ‘Laboratory of Venoms and Toxins, Institut Pasteur de Tunis, Tunisia;
Reports
and Abstracts
The marine invertebrates consist of several phylla ranging from the simplest pluricellular animals such as the sponges to animals such as the Cephalopods which have complete circulation and nervous systems. Many toxic species are to be found amongst this uniquely diversified group of organisms. The toxins involved may be divided into two groups according to the structural type to which they belong: varyingly complex organic molecules and proteinaceous compounds. In this presentation only the first group of toxic substances will be taken into consideration. The great number of bioactive secondary metabolites that have been isolated from the tissues of marine invertebrates are most often assumed to have a defensive function (predator deterrence, prevention of fouling, territorial competition, etc.) There exists a strong correlation between the absence of obvious physical defence mechanisms of an organism and the presence of unusual chemistry in its tissues. It is thus not surprising that the richest sources of these compounds have been sessile or slow-moving soft-bodied sponges, cnidarians, sea slugs, bryozoans and tunicates, while mobile (e.g. squid) and armoured species (e.g. crustaceans, snails) generally lack toxic secondary metabolites. The spectrum of compound types to be found in marine invertebrates is particularly impressive and can only be compared to the complexity of their structures. A survey of the different types of compounds occurring in the different classes of marine invertebrates will be made. Toxaemic action of entomopathogenic nematode bacterium complexes. N. Boemare, A. Givaudan, B. Duvic and M. Brehelin (Laboratoire de Pathologie Comparee, INRA-CNRS URA no. 2209, Universite Montpellier II, CP 101, 34095 Montpellier cedex 5, France). The broad host range of the entomopathogenic nematodes Steinernema and Heterorhabditis, against several insect species, is the result of efficient pathogenic actions developed by the nematodes and their symbiotic bacteria, Xenorhabdus and Photorhabdus, respectively. Pathogenicity is frequently the result of a low insect immunity against these agents and of several weapons produced by these complexes. There exist quite frequent features of non-recognition by the insect targets. Nematodes produce several weapons, such as helminthic toxins and an immune depressive factor, and above all the vector role of nematodes which inoculate their entomopathogenic symbionts into the body cavity of insects. Many Xenorhabdus species, except X. poinarii, and many Photorhabdus were found to be pathogenic by inoculation. Exotoxins have recently been characterized for X. nematophilus and P. luminescens. Xenorhabdus exotoxin was efficient against several Lepidoptera by inoculation of few nanograms of the purified product. This toxaemic action seems to be the initial cause of mortality, especially for particular insect species which are normally resistant to bacteria. The lethal process ended in a general septicaemia. Pathogenicity of the bacteria was also due to the contribution of exoenzymatic activities (proteases, lipases, phospholipases and hemolysins). In many cases, it was quite obvious that both partners co-operate to kill the insect host. With axenic S. glaseri, or its sole symbiont X. poinarii, no entomopathogenic action was recorded, but when both partners were re-associated the entomopathogenic action was restored. The significance of interactions between these aggressive elements depends on both the insect target and the bacterial-helminthic species. Insect-selective scorpion toxins contractive and flaccid : one or two modes of action) M. Stankiewicz,’ Khalifa* and M. Pelhate’ (IInstitute of Biology and Environment Protection, N. Copernicus University, Poland; and 2Laboratory of Neurophysiology, CNRS ER 120, Angers, France).
R. Ben Torun,
The effects of different toxins obtained from Buthinae scorpion venoms on Na+ conductance in insect neuronal membrane have been studied. Experiments were performed using the double oil-gap or the patch-clamp technique in current- and voltage-clamp conditions, on isolated giant axon or DUM neurons of a cockroach, Periplaneta americana. Scorpion venom contains toxins affecting Na+ conductance in neurons: cc-toxins slow inactivation of Nat channels, while /?-toxins shift the voltage dependence of Na+ channel activation to more negative potentials. The classification into n- and B-groups has been established after studies on vertebrate preparations, Our studies, together with the study performed by biochemists, indicate that scorpion venom also comprises cc-insect toxins. Other insect toxins, contractive and flaccid (according to the nomenclature of Zlotkin et al.), have an opposite global effect on intact insects. However, both groups may primarily modify the voltage dependence and the kinetics of Na+ current activation in insects, as b-toxins do in vertebrates. It is proposed to classify both the groups as /I-like insect toxins. A better characterization of one or several /I-site(s) in insect Na+ channels is essential. Nevertheless, apparent opposite global poisoning effects would be due to quantitative rather than qualitative differences in the toxin-channel interactions.
PRESENTATIONS The abstracts
are listed alphabetically
by presenting
author
Importance of the fourth disuljide bridge in the maurotoxin structure and activity. R. Ben Khalifa,‘,’ M. Crest, M. Pelhate,’ R. Kharrat,? H. Darbon,4 M. El Ayeb,? J. Van Rietshotens H. Rochati and J.-M. SabatierS (‘Laboratory of Neurophysiology, CNRS ER120, Angers University, France; 2Laboratory of Neurobiology, CNRS UPR 9024, Marseille, France; ‘Laboratory of Venoms and Toxins, Institut Pasteur de Tunis, Tunisia;