A novel bacterial symbiont in the nematode Spirocerca lupi

ABSTRACT: BACKGROUND: The parasitic nematode Spirocerca lupi (Spirurida: Thelaziidae), the canine esophagealworm, is the causative agent of spirocercosis, a disease causing morbidity and mortality indogs. Spirocerca lupi has a complex life cycle, involving an obligatory coleopteranintermediate host (vector), an optional paratenic host, and a definitive canid host. Thediagnosis of spirocercosis is challenging, especially in the early disease stages, when adultworms and clinical signs are absent. Thus, alternative approaches are needed to promote earlydiagnosis. The interaction between nematodes and their bacterial symbionts has recentlybecome a focus of novel treatment regimens for other helminthic diseases. RESULTS: Using 16S rDNA-based molecular methods, here we found a novel bacterial symbiont in S.lupi that is closely related to Comamonas species (Brukholderiales: Comamonadaceae) of thebeta-proteobacteria. Its DNA was detected in eggs, larvae and adult stages of S. lupi. Usingfluorescent in situ hybridization technique, we localized Comamonas sp. to the gut epithelialcells of the nematode larvae. Specific PCR enabled the detection of this symbiont's DNA inblood obtained from dogs diagnosed with spirocercosis. CONCLUSIONS: The discovery of a new Comamonas sp. in S. lupi increase the complexity of the interactionsamong the organisms involved in this system, and may open innovative approaches fordiagnosis and control of spirocercosis in dogs.     

Plant-parasitic Nematode Problems in the Pacific Islands

The Pacific islands have a diverse range of food and cash crops with indigenous and introduced nematode problems. The staple food crops have serious nematode pests, such as Meloidogyne spp. on sweet potato, Hirschmanniella miticausa causing corm rot of taro, and Pratylenchus coffeae and Radopholus sp. producing tuber dry rot of yams. Bananas are infested with P. coffeae or R. similis, citrus with Tylenchulus semipenetrans, rice with Aphelenchoides besseyi, and ginger with Meloidogyne spp. and R. similis. Rotylenchulus reniformis, P. zeae, P. brachyurus, and Helicotylenchus spp. are important on all of these and other crops, such as sugarcane, passion fruit, pawpaw, and cassava. Meloidogyne spp. cause serious damage to local and introduced leaf and fruit vegetables and other crops, such as tobacco, sugarcane, pawpaw, black pepper, and pyrethrum. Many other plant-parasitic genera and species, some undescribed, occur in the Pacific, and there are many islands still to be investigated.     

植物抗线虫基因的分子定位与克隆

植物线虫严重危害农业生产并造成产量损失。抗线虫基因的分子标记定位与克隆是抗线虫基因工程的基础。现就几种植物中的抗线虫基因的分子定位及克隆进行了综述 ,同时针对已克隆的抗线虫基因所编码的蛋白质的结构特征和克隆新方法进行评述 ,并对通过遗传途径发展抗线虫品种进行了展望     

Within-wood Spatial Dispersion of the Pinewood Nematode,Bursaphelenchus xylophilus

Pinewood nematode, Bursaphelenchus xylophilus (Steiner &Buhrer) Nickle, spatial dispersion was determined in Scots pine, Pinus sylvestris L., bolts infested with the pine sawyer beetle, Monochamus carolinensis (Olivier) and in bolts without M. carolinensis. According to Taylor''s power law and Green''s index of dispersion, nematode dispersion was aggregated in both sets of bolts. The degree of aggregation did not differ significantly between beetle-infested and noninfested bolts, suggesting that the presence of M. carolinensis does not affect nematode dispersion within a bolt. Nematode population densities differed radially in bolts not infested with pine sawyers, but in a nonregular pattern. Moisture content of the bolts was correlated with population density of B. xylophilus, suggesting that nematode aggregates occur in areas of high moisture content.     

Role of dung beetle feeding mechanisms in limiting the suitability of species as hosts for the nematode Spirocerca lupi

Various species of dung beetle serve as intermediate hosts after ingesting the embryonated eggs (11–15 × 30–37 µm) of Spirocerca lupi (Spirurida: Spirocercidae) in dog faeces. The feeding mechanisms of coprophagous dung beetles restrict the size of the food particles they can ingest and hence may determine which species can be efficient vectors for S. lupi. In this study, we aimed to exclude certain dung beetle species as possible hosts of S. lupi based on whether or not they ingested latex beads of known diameters mixed into fresh cattle dung. We found that the majority (11/14) of species tested can potentially serve as intermediate hosts of S. lupi because their mouthparts allow the passage of food particles larger than the minimum size range of the eggs of this parasite.     

Biocontrol: Fungi as Nematode Control Agents

The fungal antagonists of nematodes consist of a great variety of organisms belonging to widely divergent orders and families of fungi. They include the nematode-trapping fungi, endoparasitic fungi, parasites of nematode eggs and cysts, and fungi which produce metabolites toxic to nematodes. The diversity, adaptations, and distribution of nematode-destroying fungi and taxonomic problems encountered in their study are reviewed. The importance of nemato-phagous fungi in soil biology, with special emphasis on their relationship to populations of plant-parasitic nematodes, is considered. While predacious fungi have long been investigated as possible biocontrol agents and have often exhibited spectacular results in vitro, their performance in field studies has generated little enthusiasm among nematologists. To date no species has demonstrated control of any plant pest to a degree achieved with nematicides, but recent studies have provided a much clearer concept of possibilities and problems in the applied use of fungal antagonists. The discovery of new species, which appear to control certain pests effectively under specific conditions, holds out some promise that fungi may be utilized as alternatives to chemical control after a more thorough and expanded study of their biology and ecology.     

Impact of Conservation Tillage on Nematode Populations

Literature reporting the development of conservation tillage and the research that has been conducted on nematode control in crops grown in conservation tillage systems is reviewed. Effects of different types of conservation tillage on population densities of various nematode species in monocropping and multicropping systems, effects of tillage on nematode distribution in the soil profile, effects of conservation tillage on nematode control, and the role of nematology in conservation tillage research are discussed.     

A comparison of the prevalence of Spirocerca lupi in three groups of dogs with different life and hunting styles

The prevalence of Spirocerca lupi in 260 privately owned dogs with different life and hunting styles in Greece was based on the examination of randomly taken faecal samples using Teleman's sedimentation technique. The dogs did not demonstrate any clinical signs of spirocerciasis. Although the prevalence was 10%, it was found to be significantly higher in trace hunting dogs (21%), than in scent hunting dogs (5%) and household pets (0%). There was no relationship between prevalence and age/sex of dogs. The impact of life and hunting styles on the prevalence of S. lupi in the dog and that of the faecal examination technique, are discussed.     

Resistance and Resistant Reaction of Gossypium arboreum to the Reniform, Nematode,Rotylenchulus reniformis

Gossypium arboreum ''Nanking CB 1402'' possessed a high level of resistance to Rotylenchulus reniformis. Within 16 h, the nematode penetrated roots of resistant and susceptible cottons equally. After 36 h, significantly fewer nematodes were found in resistant roots. Larvae fed in either an endodermal or pericyclic cell and had no specificity for root tissue of a particular age. In roots of resistant G. arboreum ''1402,'' wall breakdown of pericyclic cells was evident after 3 d, endodermal and cortical cells collapsed, and the hypertrophied pericyclic cells disintegrated within 12 d. Cell walls immediately adjacent to the nematode''s head were thickened and more safranin positive in resistant than in susceptible cotton cultivars. Several other cultivars of G. arboreum were also resistant to R. reniformis, based on nematode fecundity and percent egg reduction.     

Preschoolers Categorize Animate Objects Better in the Presence of a Dog

ABSTRACT

The current study was designed to examine whether preschool children categorize picture stimuli differentially in the presence of a real dog compared with a stuffed dog or a human. Seventeen preschool children (age in months; M = 51.67, SD = 8.06), both Typical and those with a developmental delay (“Identified”), were asked to categorize Animate and Inanimate objects into two environments (Farm and Ocean) in each of three Collaborator conditions (Real Dog, Stuffed Dog, and Human). As predicted, there was a main effect of animation: the children more accurately categorized Animate (e.g., cow) exemplars than Inanimate ones (e.g., tractor). Additionally, the Animation variable interacted with Collaborator, such that in the presence of the real dog the impact of animation was significant, but this effect was not significant in the presence of the stuffed dog or human. This result indicates that the presence of the real dog served as a highly salient stimulus which encouraged the children to focus more of their attention on other animate objects in the list. This result provides additional evidence that the presence of a dog helps preschool children to restrict their attention to the demands of the task. This is a new and interesting finding that indicates that the presence of a real dog does have an impact on cognitive task performance.     

Potential for Nematode Control by Mycofloras Endemic in the Tropics

Results of mycological surveys of root-knot and cyst nematodes from tropical regions indicate that most fungal species associated with females or cysts of species of Globodera, Heterodera, and Meloidogyne are those found with nematodes from temperate areas. Some fungal species, however, were found in higher frequency in tropical regions than in temperate countries; e.g., Cylindrocarpon destructans and Ulocladium atrum were the most common species associated with G. pallida and G. rostochiensis cysts in Peru. These fungi are not so frequent in nematodes from temperate areas. Fungi associated with diseased nematodes in the tropics vary greatly in nutritional requirements and include thermophilic species as well as cold-tolerant fungi. Multi-cropping systems possible in most tropical regions may be designed to increase the frequency of occurrence of microbial species antagonistic to phytonematodes.