Microsporidian xenomas in fish seen in wider perspective

The history of understanding xenoparasitic complexes or xenomas provoked in the host cell by various protists and especially by microsporidia is outlined. Microsporidia have been known to produce xenomas in oligochaetes (e.g., genera Bacillidium, Burkea, Hrabyeia, Jirovecia, species of the collective group Microsporidium), crustaceans (e.g., Abelspora, Mrazekia), insects (e.g., Polydispyrenia, Thelohania) and poikilothermic vertebrates, mostly fish (Alloglugea, Amazonspora, Glugea, Ichthyosporidium, Loma, Microfilum, Microgemma, Neonosemoides, Pseudoloma, Spraguea, Tetramicra). An overview of characters of xenomas caused by species of these genera is presented. The study of microsporidia causing xenomas in fish offers an insight into cell pathology and is of interest since many of these species are important agents of diseases in commercial fish. Xenomas produced from a few types of target cell display a complete change of organisation of the host cell and differ, according to the agent, in their structure. Recent data show that proliferation of the parasite may have already started in the cells transporting the parasites to the final site of xenoma formation. However, these are preliminary revelations and most of the facets of the life cycle are still to be clarified. Curiously, xenoma-forming microsporidia do not seem to be strictly host specific. The salient features of fish microsporidian xenomas are discussed, such as role of the xenoma, whether its features are host- or microsporidium-dependent, development and demise of the xenoma in the course of time, and host reaction phenomena. The need of further research is emphasised.     

Comet assay in gill cells of Prochilodus lineatus exposed in vivo to cypermethrin

Agricultural chemicals can induce genetic alterations on aquatic organisms that have been associated with effects on growth, reproduction and population dynamics. The evaluation of DNA damage in fish using the comet assay (CA) frequently involves the utilization of erythrocytes. However, epithelial gill cells (EGC) can be more sensitive, as they are constantly dividing and in direct contact with potentially stressing compounds from the aquatic environment. The aim of the present study was to evaluate (1) the sensitivity and suitability of epithelial gill cells of Prochilodus lineatus in response to different genotoxic agents through the application of the CA, (2) the induction of DNA damage in this cell population after in vivo exposure to cypermethrin. Baseline value of the CA damage index (DI) for EGC of juvenile P. lineatus was 144.68 ± 5.69. Damage increased in a dose-dependent manner after in vitro exposure of EGC to methyl methanesulfonate (MMS) and H₂O₂, two known genotoxic agents. In vivo exposure of fish to cypermethrin induced a significant increase in DNA DI of EGC at 0.150 μg/l (DI: 239.62 ± 6.21) and 0.300 μg/l (270.63 ± 2.09) compared to control (150.25 ± 4.38) but no effect was observed at 0.075 μg/l (168.50 ± 10.77). This study shows that EGC of this species are sensitive for the application of the CA, demonstrating DNA damage in response to alkylation (MMS), oxidative damage (H₂O₂), and to the insecticide cypermethryn. These data, together with our previous study on DNA damage induction on erythrocytes of this species, provides useful information for future work involving biomonitoring in regions where P. lineatus is naturally exposed to pesticides and other genotoxic agents.     

Mechanisms of herbicide sorption in microalgae and the influence of environmental factors

The sorption kinetics of photosystem II herbicides in the unicellular microalgae Ankistrodesmus braunii are independent of the herbicide concentration. While diuron-type herbicides attain an equilibrium state of sorption after at most 5 min, it takes up to 60 min for phenol-type herbicides. The kinetics of the inhibition of photosynthetic electron transport display a good correlation to the kinetics of sorption. For both types of herbicides, a phase of prevalent partitioning into the lipid phase of the cell membranes preceeds binding to thylakoid membranes. With phenol-type herbicides this phase is much more extended than with diuron-type compounds. As a consequence, there is no displacement of previously bound herbicides of this type from algal cells by addition of an excess of other photosystem II herbicides. The sorption of phenol-type herbicides to microalgae is under strong influence of environmental factors, such as light, temperature, pH, or oxygen concentration. Thus, besides the lipophilicity of these biocides, the response of the target cells to environmental factors is at least as important for herbicide sorption in the cells. From these results it is concluded that a prediction of the biocide accumulation in aquatic microorganisms can only be partly deduced from the properties of the pesticide molecule. The target cells and their complex responses to their environment strongly relativize correlations of chemical properties, e.g., lipophilicity and biological activity.     

禾草灵的作用机制及环境生态效应研究进展

禾草灵 (diclofop-methyl)属芳氧苯氧丙酸类除草剂,广泛应用于禾本科杂草防除,其降解受到土壤有机质含量、pH值、氧气等众多因素的影响。母体化合物禾草灵及其主要降解产物禾草灵酸都具有除草活性,并会对环境中的一些非靶标生物产生急性或慢性毒性,是一类环境内分泌干扰物及过氧化物酶体增殖剂;同时,由于部分杂草产生抗性,进而演替成优势种群,迫使禾草灵的用量增加,更加重了其环境压力。文章就禾草灵的作用机制,其在环境中的降解、吸附等行为以及对非靶标生物的生态效应进行了综述,探讨了其中存在的一些问题,如生态毒理尤其是对映体差异性在毒性方面数据的缺乏等,并对今后的发展方向进行了展望。     

Advances in the knowledge of amphizoic amoebae infecting fish

Free-living amoebae infecting freshwater and marine fish include those described thus far as agents of fish diseases, associated with other disease conditions and isolated from organs of asymptomatic fish. This survey is based on information from the literature as well as on our own data on strains isolated from freshwater and marine fish. Evidence is provided for diverse fish-infecting amphizoic amoebae. Recent progress in the understanding of the biology of Neoparamoeba spp., agents responsible for significant direct losses in Atlantic salmon and turbot industry, is presented. Specific requirements of diagnostic procedures detecting amoebic infections in fish and taxonomic criteria available for generic and species determination of amphizoic amoebae are analysed. The limits of morphological and non-morphological approaches in species determination are exemplified by Neoparamoeba, Vannella and Platyamoeba spp., which are the most common amoebae isolated from fish gills, Acanthamoeba and Naegleria spp. isolated from various organs of freshwater fish, and by other unique fish isolates of the genera Nuclearia, Thecamoeba and Filamoeba. Advances in molecular characterisation of SSU rRNA genes and phylogenetic analyses based on their sequences are summarised. Attention is particularly given to specific diagnostic tools for fish-infecting amphizoic amoebae and ways for their further development.     

Detection of iron in tissues from slugs (deroceras reticulatum müller) after ingestion of iron chelates,by means of energy-filtering transmission electron microscopy (EFTEM)

Two iron chelates, one toxic (iron ‘butan’) and the other not (iron ‘octan’), were ingested by slugs (Deroceras reticulatum) at either a low (5 g kg⁻¹ diet) or a high (100 g kg⁻¹ diet) dose rate. In tissue sections of the digestive gland and body wall, iron was detected by energy-filtering transmission electron microscopy (EFTEM), using electron spectroscopical imaging (ESI) and electron energy-loss spectroscopy (EELS). The strongest signals for iron were obtained in secondary lysosomes of the resorptive cells in the digestive gland of slugs treated with a low dose of either compound, or with the high dose of iron ‘octan’. At the cell apices of these cells, in endocytotic vesicles and in apically located lysosomes, iron was detected only in slugs fed with either dose of iron ‘octan’. In slugs fed with the high dose of iron ‘butan’, iron could clearly be localised in the epithelial and mucus cells of the skin. The results are discussed with respect to differences in the toxicity of the two iron chelates. © 1999 Society of Chemical Industry     

Humoral intestinal immunity against Encephalitozoon cuniculi (Microsporidia) infection in mice

Three strains of mice, BALB/c, IL-12 knock-out (KO) and INF-gamma knock-out, were chosen as an experimental model for the study of intestinal immunity induction against Encephalitozoon cuniculi Levaditi, Nicolau et Schoen, 1923 infection. Mice were infected perorally with 10(7) spores and re-infected with the same dose 70 days after the first infection. The anti-E. cuniculi IgA, IgG and IgM responses in sera and extracts of stool samples were determined by ELISA. Results have shown specific antibody production in the sera and intestinal secretions of all three strains of mice induced orally by E. ciniculi spores. BALB/c mice developed a stronger humoral immune response than IL-12 KO mice. The lowest antibody response developed in INF-gamma KO mice that succumbed to the infection within 28 days post infection.     

Post-embryonic development of Camallanus cotti (Nematoda: Camallanidae), with emphasis on growth of some taxonomically important somatic characters

In this paper, the quantitative post-embryonic development of the Asian freshwater fish nematode Camallanus cotti Fujita, 1927, is described. Larval and adult morphometrics were obtained by following the parasite's life cycle experimentally using copepods Macrocyclops albidus (Jurine) as intermediate host and guppies Poecilia reticulata (Peters), southern platyfish Xiphophorus maculatus (Günther) and paradise fish Macropodus opercularis (L.) as definitive host. Additionally, adult worms were obtained from heavily infected paradise fish imported from Singapore. It is suggested that the gradual change in proportions of the worm's somatic body parts reflects the specific ecological role of each developmental stage. The free-living infective first-stage larva seems to be adapted for transmission, as indicated by its relatively long tail, designed to generate host-attracting movements, and its non-functional intestine. The second- and third-stage larvae from the copepod intermediate host seem mainly to invest in trophic functionality, i.e., the development of the buccal capsule and the oesophagus, which are crucial structures for the worm's successful establishment in the definitive fish host. Once in the fish intestine, the larvae enter a period of considerable growth. After the fourth (i.e., last) moult, a 72% increase in average female body length occurs. This is accompanied by doubling the average vulva-tail tip distance and the average tail length. The length of the female hind body expands in an accelerating allometric fashion, and seems to be closely linked to the posterior-wards expansion of the uterus. In the males however, growth seems to cease after the final moult. We conclude that female post-maturational body size, but especially the length of the hind body and the tail, are closely related to reproductive state, i.e., the developmental stage of the offspring in the uterus, and, probably, the worms' age. Any future taxonomical studies of camallanids in general, and C. cotti in particular, should thus be aware of the reproductive state of the females used.     

Four new species of Cichlidogyrus (Monogenea: Ancyrocephalidae), gill parasites of Tilapia cabrae (Teleostei: Cichlidae), with discussion on relative length of haptoral sclerites

Tilapia cabrae Boulenger, 1899, a cichlid fish from coastal lowlands of the Republic of Congo (Africa), was examined for gill parasites. Four new species of the Monogenea were found, all belonging to Cichlidogyrus (Ancyrocephalidae): C. berradae sp. n., C. revesati sp. n., C. legendrei sp. n., and C. lemoallei sp. n. A possible relationship between the relative size of haptoral sclerites (i.e., uncinuli compared to gripi) and microhabitat selection in the studied host-parasite model is discussed.     

Measurement of the bioconcentration factors of pesticides by freshwater fish and their correlation with physicochemical properties or acute toxicities

The bioconcentration factors (BCF) for 15 pesticides by a freshwater fish (topmouth gudgeon) were measured under continuous flow conditions in water containing 5 to 20 μg litre^?1 of each pesticide at the equilibrium condition. A significant correlation was found between the BCF by the fish and the water solubility of the pesticide or its partition coefficient (PC) between octan-1-01 and water. Moreover, a significant correlation was also found between the BCF by topmouth gudgeon and the acute toxicities to carp, rainbow trout and water flea. It would therefore appear that the bioconcentration potential of a pesticide by a fish may be predicted from knowledge of its solubility or PC, and that the acute toxicity of a pesticide to a fish may be predicted from knowledge of the BCF.     

Effect of tick salivary gland extract on the cytokine production by mouse epidermal cells

Previous studies have demonstrated that both tick saliva and Borrelia burgdorferi sensu lato antigens modulate the cytokine response of the host. In this paper, the effect of salivary gland extract (SGE) from Ixodes ricinus (L., 1758) ticks on cytokine production by primary cultures of mouse epidermal cells stimulated with Borrelia afzelii Canica, Nato, du Merle, Mazie, Baranton et Postic, 1993 spirochetes was analysed. Epidermal cells were derived from C3H/HeN mice, susceptible to Lyme disease, and BALB/c mice, which are resistant. In cultures from C3H/HeN mice, SGE down regulated production of tumour necrosis factor alpha (TNF-alpha) and up regulated Th2 cytokine, interleukin 4 (IL-4). Cultures from BALB/c mice produced higher basal levels of monitored cytokines, but their production was affected by SGE a different way. While Th2 cytokines IL-6 and IL-10 were down regulated, the effect on TNF-alpha and IL-4 was ambiguous. These results indicate that the effect of tick saliva on the epidermal cells of Lyme disease-susceptible C3H/HeN mice mirrors its effect on other cells of the immune system.     

The pathogenicity of Cryptosporidium parvum Tyzzer, 1912 and C. Baileyi Current, Upton et Haynes, 1986 for chickens

Clinical symptoms and pathological-morphological changes in the respiratory tract of chickens inoculated with Cryptosporidium parvum were described for the first time and compared with those induced by Cryptosporidium baileyi. Intratracheal inoculation with these two species caused symptoms of a respiratory tract disease in all chicken, but a disease of the digestive tract or death did not occur in any case. Pathological and morphological changes were observed only in the respiratory system and were characterized by petechiae in the mucous of larynx, trachea, primary bronchi and in the wall of air sacs in chickens infected with C. parvum, or by diffuse hyperaemia of respiratory tract mucosa in chickens infected with C. baileyi. The pathological-histological changes, which were characterized by affections of various degrees in epithelial cells, mucous glands, and lamina propria mucosae, were more pronounced in the chickens infected with C. parvum.     

黏虫黑化引起的免疫致灾新机制的思考

本文根据田间发现的黏虫大发生迁飞种群的多数个体均发生了不同程度黑化的现象,结合近年来迁飞昆虫的密度依赖性防御能力、体液免疫与细胞免疫应答机制、防御的神经内分泌调控机制以及生态免疫等方面的研究进展,提出黏虫防御反应及其与迁飞致灾关系的思考,对于揭示迁飞性黏虫成灾新机制以及指导其生物防治均具有重要意义。     

An epidemiological simulation model with three scales of spatial hierarchy

ABSTRACT An epidemiological model integrating three organizational scales of host plant populations (e.g., sites, leaves, and plants) is presented. At the lowest (site) scale, the model simulates the dynamics of vacant, latent, infectious, and removed sites. Three types of vacant sites are distinguished, depending on presence of infections at higher scales (leaf or plant). The rate of infection of each type of vacant site is computed according to ratios of autodeposition, allo-leaf-deposition, and allo-plantdeposition. At the leaf and plant scales, the rate of victimization is a function of the rate of infection of vacant sites. Sensitivity analyses showed that deposition patterns (the relative proportions of auto-, allo-leaf-, and allo-plant-depositions) and host structure (leaf size and number of leaves per plant) affected the speed of epidemics at the different scales. Model outputs conformed with results from other approaches in the case of random distribution of the disease. The model hypotheses concerning infection from autodeposited propagules, and their implications for disease epidemics, are discussed. The model can be used to derive relationships between allo-deposition ratios and disease incidences at the three scales. These relationships become simple when disease intensity is low. These relationships may be useful, e.g., to assess the potential efficiency of cultivar mixture to control epidemics. Integration of different organization scales and allo-deposition parameters enables the model to capture important features of epidemics developing in space without using explicitly spatialized variables. Such an approach could be useful to analyze other ecological processes that involve a variety of scales.     

OsDCL1基因沉默突变体诱导稻瘟病抗性的转录组分析

稻瘟病是严重危害水稻生长的真菌病害,每年给水稻生产带来重大经济损失。与野生型日本晴NPB相比,OsDCL1基因沉默突变体增强了水稻对稻瘟菌的广谱抗病性。为了解水稻OsDCL1-RNAi突变体的抗病机制,我们分析和比较了它和野生型日本晴NPB在稻瘟菌侵染前后转录组水平的变化。响应稻瘟菌侵染的7 129个差异表达基因(DEGs)中,NPB和OsDCL1-RNAi突变体分别有5 382和5 180个基因表达发生了变化,参与生物胁迫反应、信号通路、蛋白代谢和RNA调控4个通路的基因明显被富集。以野生型未受稻瘟菌侵染的基因表达为对照,在OsDCL1-RNAi突变体中共发现1 318个DEGs,且超过70%是上调的,其中很多基因参与了生物胁迫反应(26.9%)和信号通路(11%),上调表达基因中与生物胁迫反应相关的主要为PR基因和细胞壁相关基因。另外,还发现10个茉莉酸相关基因和11个水杨酸相关基因分别在OsDCL1-RNAi突变体中显著下调和上调表达。在OsDCL1-RNAi突变体中还发现WRKY和MYB等一些转录因子家族以及部分受体类激酶被诱导表达。用qRT-PCR方法验证部分差异表达的基因,其结果与DEGs基本一致。OsDCL1-RNAi突变体中转录组变化的分析,为深入了解该突变体抗瘟性增强的机制奠定了基础。     

三唑磷对麦穗鱼脑组织中乙酰胆碱酯酶的诱导

为了检测有机磷杀虫剂对鱼脑组织中乙酰胆碱酯酶(AChE, EC 3.1.1.7)的诱导,采用间接非竞争酶联免疫吸附测定法(ELISA)检测了三唑磷胁迫下麦穗鱼Pseudorasbora parva脑组织中乙酰胆碱酯酶含量的变化。当暴露浓度仅为0.1 μg /L时,三唑磷即对AChE产生诱导。由于存在诱导效应,三唑磷对酶活性的抑制在一定程度上被酶蛋白含量的提高所掩盖。研究结果表明,以酶蛋白替代总蛋白来衡量粗酶液中AChE的活性,可以明显提高对有机磷胁迫作用的检测灵敏度。     

Multiple facets of response to fungicides – the influence of azole treatment on expression of key mycotoxin biosynthetic genes and candidate resistance factors in the control of resistant <Emphasis Type="Italic">Fusarium</Emphasis> strains

The spread of fungicide resistant and/or tolerant phytopathogenic fungi is an important factor affecting crop protection. However, the mechanisms of fungal response to fungicide application are not entirely characterised. In particular, the contribution of previously known resistance factors and the final influence of fungicide treatments on metabolism of surviving mycelia (e.g. mycotoxin increased release and biosynthesis potentially causing contamination of the crops) merit investigation, in order to improve future molecular diagnostics of fungicide resistant strains. The performed experiments have shown distinct expression changes for homologs of a known fungicide resistance factor Flr1 (yeast; DHA1 family of major facilitator superfamily transporters) after azole application in cultured fusaria. Two distantly related homologs of that gene were selected, based on the unsupervised clustering and phylogenetic analysis of transporter sequences. One of these (FGSG_02865), was found to occur across the Fusarium sambucinum complex (F. graminearum, F. culmorum, F. cerealis) and was upregulated starting 24 h after fungicide treatments. This delayed response may point to possible involvement of DHA1 antiporters in a generalised response to stress resulting from fungicide treatment. Additional expression profiling was conducted for the mycotoxin biosynthetic genes (trichothecene and zearalenone gene clusters) in strains of Fusarium sambucinum complex cereal pathogens. The expression changes, when subjected to treatment with the fungicides (flusilazole, carbendazim), show that even an effective treatment (in this study, the benzimidazole fungicide carbendazim) applied to the grown mycelium, can result in enhanced activation of mycotoxin biosynthetic genes in fungal cells which survive the treatment. Our results suggest that increased mycotoxin contamination can be strongly influenced not only by the amount or the type of antifungal compound, but also the timing of fungicide exposition (stage of infection).     

The 5' Third of Cauliflower mosaic virus Gene VI Conditions Resistance Breakage in Arabidopsis Ecotype Tsu-0

ABSTRACT Arabidopsis thaliana ecotypes vary in their responses to viruses. In this study, we analyzed the variation in response of A. thaliana ecotype Tsu-0 to Cauliflower mosaic virus (CaMV). This ecotype was previously reported to be resistant to two CaMV isolates (CM1841 and CM4-184), but susceptible to W260. In this study, we show that Tsu-0 is resistant to four additional CaMV isolates. CaMV propagated within the rosette leaves of Tsu-0 plants, but did not appear to spread systemically into the inflorescence. However, virus viability in rosette leaves of Tsu-0 plants apparently was not compromised because infectious CaMV could be recovered from these organs. W260 overcomes Tsu-0 resistance by a passive mechanism (i.e., this virus avoids activating plant defenses). The portion of the viral genome responsible for W260 resistance breakage was mapped to the 5' third of gene VI, which we have termed RBR-1. This region is also responsible for controlling the ability of CaMV to infect different types of solanaceous plants. Hence, the pathways by which plants of different families interact with CaMV may be conserved through evolution.     

On the biochemistry of interference with normal plant development,with special reference to growth regulators

The precisely “tuned” balance between regulatory mechanisms at various levels, which in fact forms the base of normal development, differentiation and growth of plants, can be disturbed by very different factors.These may be chemical (toxic) agents, either applied intentionally (herbicides, growthretardants) or introduced by pathogenic microorganisms (cf. wilting caused by parasites), plant viruses and different, mostly unknown factors, which in combination with an essential wounding process, may induce plant tumors.Apart from these, physical factors e.g. variations in light intensity and temperature have to be considered.It is analyzed to what extent these seemingly divergent problems may be put on a common biochemical (physiological) base, especially because of the fact that the morphologically perceptible effects evidently often are concerned with a shift in the normal pattern of interrelationships of growth regulators (auxins).