Growth of Certain Aquatic Oomycetes on Amino Acids II. Apodachlya, Aphanomyces, and Pythium

Four aquatic fungi —Apodachlya brachynema and A. minima (Leptomitales), Aphanomyces laevis (Saprolegniales), and Pythium ultimum (Peronosporales) —were tested for growth in synthetic media containing one of a variety of carbon sources. Apodachlya brachynema readily utilized five amino acids — alanine, glutamate, aspartate, proline and leucine — as well as glucose and acetate. Growth on sucrose as a carbon source was slight. Apodachlya minima differed from A. brachynema in that it could not utilize proline and leucine. Aphanomyces laevis grew well on only three of the substrates tested — glucose, alanine and glutamate. Pythium ultimum utilized glucose, sucrose, maltose, cellobiose, alanine, glutamate, aspartate, proline, asparagine, ornithine, and serine, but not eight other amino acids. All of these fungi hydrolyzed gelatin. Radioactively labeled carbon dioxide was released during incubation of Aphanomyces laevis in media containing labeled leucine, proline, or phenylalanine. These data provide evidence of some catabolism of the three substrates although none of these substrates can support the growth of Aphanomyces laevis as a sole source of carbon and nitrogen.     

Aplanes braunii (Phylum Oomycota) causes mortality in Anabas cobojius

The fresh water fish Anabas cobojius (Hamilton-Buchanan 1822), was found to be parasitised by Aplanes braunii de Bary 1888. It is the first report of Aplanes braunii to cause disease on any fish. A. braunii is a virulent parasite that caused cotton-wool disease involving the skin, fins and muscles of A. cobojius. The hyphae also penetrated deep into the tissues of the infected fish and all of them ultimately died.This revised version was published online in October 2005 with corrections to the Cover Date.     

Unexpected progeny obtained from glasshouse study of soil pH influence onAcaulospora laevis inoculum

Summary Potential growth stimulation of two hosts by acid-tolerantAcaulospora laevis was tested in a soil adjusted to 5 pH levels from 5.0 to 7.7. By wet-sieving methods, the field-source inoculum was essentially a pure culture ofA. laevis spores. Upon harvest of sweetgum a completely different spore-type was found in large quantities;A. laevis spores were relatively few to non-existent. The results dramatically underscore the need for caution against relying solely on pre-trial identifications of inoculum spores or presuming that apparently single-species cultures/inoculum will remain pure throughout an experiment.Contribution of the Oregon State University Agricultural Experiment Station in cooperation with the US Department of Agriculture, Agricultural Research Service, technical paper #7366 of the former.     

Record of a fatal oomycotic disease of the fresh water fish Anabas cobojius in India caused by Aplanes braunii

The fresh water fish Anabas cobojius (Hamilton-Buchanan 1822), was found to be parasitised by Aplanes braunii de Bary 1888. It is the first and only report of any Aplanes de Bary to cause disease on any fish. A. braunii was found to be a virulent parasite ofA. cobojius causing cotton-wool disease involving the skin and fins. The hyphae also penetrated into the tissues of the infected fish and all of them ultimately died.This revised version was published online in October 2005 with corrections to the Cover Date.     

Comparisons of within-population genetic variation in sexual and agamospermousAmelanchier (Rosaceae) using RAPD markers

We compared genetic variation of sexualAmelanchier bartramiana and facultatively agamospermous (asexually seed-producing)A. laevis at one site where the two species are sympatric. We analyzed 77 random amplified polymorphic DNA (RAPD) markers in 29A. bartramiana individuals and 76 RAPD markers in 31A. laevis individuals. The two species do not differ significantly in mean genetic variation. However, 22.4% of genetic similarity values betweenA. laevis individuals exceed the highest value ofA. bartramiana and may represent the effect of agamospermy. Variation withinA. laevis may be the result of sexuality, hybridization, polyploidy, and other factors.     

异角毛藻和平滑角毛藻的分类学修订

为了澄清异角毛藻和平滑角毛藻的分类学疑问,在广东南澳岛海域建立了单克隆培养株系,利用光学显微镜和电子显微镜技术,开展了基于生活史的连续形态学观察,发现粗大角毛的延伸方向易变,是不稳定特征,不宜继续赋予分类学价值。对核糖体大亚基编码基因的D1～D3区序列进行扩增和分析,结果异角毛藻和平滑角毛藻的目标基因序列基本一致,仅有1个平滑角毛藻株系存在2个差异碱基。因此,两者具有一致的系统学位置,属于同一物种,平滑角毛藻应该是异角毛藻的同种异名。     

Subdivision of the genus Pleuroxus (Anomopoda,Chydoridae) into subgenera worldwide

Examination of many species of Pleuroxus from the entire World has revealed a major dichotomy in morphology, one line related to aduncus: the other to laevis both from Europe. Pleuroxus trigonellus (the type species of the genus) and Peracantha truncata are in two other distinct lines. The new subgenus Tylopleuroxus is proposed for the species related to aduncus, and the subgenus Picripleuroxus for those related to laevis. Tylopleuroxus is primarily Southern Hemisphere in distribution, Picripleuroxus primarily Northern Hemisphere. Evidence thus far suggests that probably most, perhaps all, of the taxa are confined to single continents or land masses. Deceased     

Studies in parasitic watermolds of Kumaun Himalayas: The host range of five species of olpidiopsis

The host range of five species of Olpidiopsis in some species of Achlya, Aphanomyces, Brevilegnia, Isoachlya, Saprolegnia, Thraustotheca and Pythium was studied. Species were different in their host range.     

Proteomic approach: Identification of <Emphasis Type="Italic">Medicago truncatula</Emphasis> proteins induced in roots after infection with the pathogenic oomycete <Emphasis Type="Italic">Aphanomyces euteiches</Emphasis>

The legume root rot disease caused by the oomycete pathogen Aphanomyces euteiches is one major yield reducing factor in legume crop production. A comparative proteomic approach was carried out in order to identify proteins of the model legume Medicago truncatula which are regulated after an infection with A. euteiches. Several proteins were identified by two dimensional gel electrophoresis to be differentially expressed after pathogen challenge. Densitometric evaluation of expression values showed different regulation during the time-course analysed. Proteins regulated during the infection were identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Among the differentially expressed proteins, two encoded putative cell wall proteins and two were designated as small heat shock proteins. Furthermore, an isoform of the chalcone-O-methyltransferase was found to be increased in infected roots. The majority of induced proteins belonged to the family of class 10 of pathogenesis related proteins (PR10). Previously, various PR10-like proteins have been shown to be regulated by general stress or abscisic acid (ABA). Therefore, these proteins were further investigated concerning their regulation in response to drought stress and exogenous ABA-application. Complex regulation patterns were identified: three of the A. euteiches-induced PR10-like proteins were also induced by exogenous ABA- but none of them is induced after drought stress. In contrast, three of these proteins are down-regulated by drought stress. Hence, the strong expression of different PR10-family members and their regulation profiles indicates that this set of proteins plays a major role during root adaptations to various stress conditions.     

Spiny-cheek crayfish Orconectes limosus carry a novel genotype of the crayfish plague pathogen Aphanomyces astaci

The oomycete Aphanomyces astaci causes mass mortalities of European crayfish. Different species of North American crayfish, original hosts of this parasite, seem to carry different strains of A. astaci. So far, four distinct genotype groups have been recognised using Random Amplification of Polymorphic DNA (RAPD-PCR). We succeeded in isolating A. astaci from the spiny-cheek crayfish Orconectes limosus, a widespread invader in Europe, and confirmed that this species carries a novel A. astaci genotype. Improving knowledge on the diversity of this parasite may facilitate identification of genotypes in mass mortalities of European crayfish, thus tracing the sources of infection.     

Proteomic Profiling Unravels Insights into the Molecular Background Underlying Increased <Emphasis Type="Italic">Aphanomyces euteiches</Emphasis>-Tolerance of <Emphasis Type="Italic">Medicago truncatula</Emphasis>

To investigate the molecular mechanisms underlying susceptibility of legumes to the root pathogen Aphanomyces euteiches (oomycota), comparative proteomic studies have been carried out. In a first approach, we have analysed two Medicago truncatula lines of the French CORE collection (F83.005-5 (R2002) and F83.005-9 (R2002)), which showed either increased or decreased susceptibility to A. euteiches as compared to the widely adopted line A17. Several proteins were identified to be differentially induced after pathogen challenge in the two M. truncatula accessions with altered disease susceptibility, whereof proteins with increased abundances in the more resistant line F83.005-9 could be involved in mechanisms that lead to an improved disease resistance. Among these proteins, we identified two proteasome alpha subunits, which might be involved in defense response. To broaden our studies on A. euteiches-tolerance of M. truncatula, we investigated two other phenomena that lead to an either increased A. euteiches-resistance or to an enhanced susceptibility. The topic of an enhanced plant resistance to A. euteiches was studied in plants showing a bioprotective effect of a pre-established arbuscular mycorrhiza (AM) symbiosis. Evaluation of root fresh weights and pathogen spreading in the root system clearly indicate that mycorrhizal plants show increased A. euteiches-resistance as compared to non-mycorrhizal plants. Proteome analyses revealed the induction of similar protein patterns as in the M. truncatula accessions with comparatively high resistance level to A. euteiches. In a third approach, increased A. euteiches susceptibility was effected by exogenous abscisic acid (ABA) application prior to root infection. Evaluation of the abundance levels of a group of pathogenesis related class 10 (PR10)-like proteins, which were previously identified to be regulated after A. euteiches infection, revealed a correlation between the abundance levels of these proteins and the A. euteiches infection level or severity. Requests concerning seeds from the Medicago truncatula lines F83.005-5 and F83.005-9 should be addressed to Jean-Marie Prospéri, INRA-SGAP Laboratory, Laboratoire de Ressources Génétiques et d’Amélioration des Luzernes méditerranéennes, Mauguio, France, jean-marie.prosperi@ensam.inra.fr.     

Water quality as a determinant of the composition of fish parasite communities

To investigate the relationship between fish parasite communities and water quality level, metazoan parasites were examined in 157 specimens of chub (Leuciscus cephalus L.), sampled in four lowland water courses (northern Italy): Ticino river (unpolluted), Naviglio Pavese Canal (slightly polluted), Lambro river near the Merone village (polluted) and near Monza (severely polluted). Dactylogyrus vistulae, Paradiplozoon ergensi, Bucephalus polymorphus, Acanthocephalus anguillae and larval stages of Tylodelphys clavata were found in all the sampled sites. The distribution of Lamproglena pulchella and Pomphorhynchus laevis was limited to the unpolluted and slightly polluted river sectors, while Asymphylodora tincae, glochidia, along with larval stages of Diplostomum spathaceum, were absent in the severely polluted site. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity), the degree of interactivity among parasites, as well as parameters of species richness and diversity suggest that the structure of parasite communities are affected by the water contamination level.     

The assessing of Pacific oyster (Crassostrea gigas) rearing performances by the IFREMER/REMORA network: method and first results (1993–98) in Brittany (France)

Parasitological monitoring was carried out from 1997 to 1999 in a highly saline (41–45 g/l) lake in southeastern California, Salton Sea. A total of 1473 fishes were examined. Young tilapia, Oreochromis mossambicus, croaker, Bairdiella icistia, and mudsucker, Gillichthys mirabilis, were found infected by ectoparasites. Some persistent foci of fish infestations were found around the perimeter of the lake. The diversity of parasites was limited to three protozoan species, Amyloodinium ocellatum (Dinoflagellida), Ambiphrya ameiuri (Peritricha), Cryptobia branchialis (Bodonida: Kinetoplastida), and two metazoans, the monogeneans Gyrodactylus olsoni and G. imperialis. Both A. ocellatum and A. ameiuri infested fish from spring through fall. The greatest infestations occurred in summer (29–40°C) in the case of A. ocellatum and in spring and autumn (22–27°C) in the case of A. ameiuri. High parasite loads caused severe damage to such respiratory organs as gills and skin. They may depress respiration and osmoregulation and, in combination with other environmental factors, cause fish suffocation and death. These parasites may play a major role in juvenile fish mortality.     

加州鲈源鰤鱼诺卡氏菌的分离鉴定及致病性

[背景] 鰤鱼诺卡氏菌（Nocardia seriolae）是一种严重危害水产养殖业的病原菌,可引起以体表溃疡、出血及组织器官形成结节为特征的鱼类慢性肉芽肿疾病,目前尚无有效的防治方法。[目的] 明确引起安徽省临泉县某养殖场加州鲈（Micropterus salmonoides）结节病的病原菌,探讨其致病性,为该病的有效防治提供科学依据。[方法] 取肝脏结节病灶接种于TSB培养基分离优势细菌,利用表型检查结合分子生物学方法鉴定分离菌株。进一步通过检测分离菌株的毒力基因、测定其对加州鲈的半数致死量（LD₅₀）以及所感染加州鲈的组织病理学变化与组织载菌量,分析其致病性。[结果] 从病鱼体内分离到一株优势菌株NI,综合NI分离株的表型特性、16S rRNA基因序列与鰤鱼诺卡氏菌参考株相应序列的一致性以及特异性PCR扩增结果,确定其为鰤鱼诺卡氏菌。鰤鱼诺卡氏菌NI分离株携带毒力基因gapA、ibeA和mip,人工回归感染后加州鲈出现与自然病例相似的症状,其对加州鲈的LD₅₀为2.58×10⁶ CFU/尾。组织病理学观察到头肾、心脏、肝脏、胃和脾脏均出现慢性肉芽肿病变,肠管肌层疏松、肠绒毛脱落,肌肉组织中肌纤维疏松、间隙增宽。qPCR检测结果显示,组织中鰤鱼诺卡氏菌载量由高到低依次为头肾、心、肝、胃、脾、肠和肌肉。[结论] 鰤鱼诺卡氏菌是引起此次加州鲈结节病的病原菌,对该菌致病性的研究为加州鲈诺卡氏菌病的防控提供了理论依据。     

Lineage-Specific Tandem Repeats Riding on a Transposable Element of MITE in <Emphasis Type="Italic">Xenopus</Emphasis> Evolution: A New Mechanism for Creating Simple Sequence Repeats

Xstir is a repetitive DNA sequence element that is extremely amplified as a common component of two different structures: a tandem repeat (Xstir array) and a MITE (miniature inverted-repeat transposable element) in the genome of Xenopus laevis. To elucidate the origin and evolutionary history of Xstir-related sequences, we investigated their species specificity among three Xenopus species (X. laevis, X. borealis, and X. tropicalis). Analyses by sequence alignment and digestion with restriction enzymes of genomic Xstir-related sequences revealed that the MITE (Xmix MITE) was well conserved among the three Xenopus species, with small lineage-specific differences. On the other hand, the tandem repeat element (tropXstir) in X. tropicalis was different from the Xstir that X. laevis and X. borealis have in common. Both sequences of Xstir and tropXstir were, however, different segments of the Xmix MITE. The results suggest that these tandem repeats were formed by partial tandem duplication of the MITE internal sequence in each lineage of X. tropicalis and of X. borealis/X. laevis after their branching. A molecular mechanism for creating and elongating the tandem repeats from the MITE is proposed.Reviewing Editor: Dr. Jerzy Jurka     

乌鳢源杀鱼爱德华菌的分离鉴定及药敏特性研究

【背景】江苏省扬州市某乌鳢养殖场发生疾病,给养殖户造成了严重的经济损失。【目的】确定病因并筛选出敏感药物,为乌鳢相关疾病的防治提供参考。【方法】从患病乌鳢体内分离致病菌,并从形态、生理生化特征、16S rRNA和gyrB基因序列及特异性PCR检测等方面对分离菌株进行鉴定,同时开展人工感染试验分析其致病性,通过纸片扩散法进行药敏特性分析。【结果】从患病乌鳢体内分离获得优势菌株SHL,经形态特征、理化特性、16SrRNA和gyrB基因序列及特异性PCR检测鉴定为杀鱼爱德华菌。进一步人工感染试验证实其对乌鳢有较强的致病性,LD50为1.6×105 CFU/g,发病症状与自然发病症状相似。药敏试验结果显示,该菌株对青霉素、氯霉素、四环素等28种抗菌药物高度敏感,对红霉素中度敏感,对苯唑西啉、克拉霉素、万古霉素等6种药物耐药。【结论】引起江苏省扬州市某养殖场的乌鳢体表溃烂及死亡的病原菌为杀鱼爱德华菌,这是我国首次从淡水鱼类中检出致病性杀鱼爱德华菌,表明该菌的感染谱在扩大,需引起水产养殖领域的重视,在养殖过程中可根据药敏实验结果选用合适的国标渔药进行防治。     

Arbuscular mycorrhizal fungi from three genera induce two-phase plant growth responses on a high P-fixing soil

Plant growth enhancing effects of arbuscular mycorrhizal (AM) fungi are suitably quantified by comparisons of mycorrhizal and non-mycorrhizal plant growth responses to added phosphorus (P). The ratio between the amounts of added P required for the same yield of mycorrhizal and non-mycorrhizal plants is termed the relative effectiveness of the mycorrhiza. Variation in this relative effectiveness was examined for subterranean clover grown on a high P-fixing soil. Plants were either left non-mycorrhizal or inoculated with one of three AM fungal species with well-characterised differences in external hyphal spread. With no P added, plants from all treatments produced <10% of their maximum growth achieved at non-limiting P supply. The growth response of non-mycorrhizal plants was markedly sigmoid. Mycorrhizal growth responses were not sigmoid but their shape was two-phased. The first phase was an asymptotic approach to 25–30% of maximum growth, followed by a second asymptotic rise to maximum growth. Growth effects of Glomus invermaium and Acaulospora laevis were quite similar. Plants in these treatments produced up to four times greater shoot dry biomass than non-mycorrhizal plants. Scutellospora calospora was less effective. The relative effectiveness of AM fungi varied with the level of P application. This is expected to apply to all soils on which a sigmoid response is obtained for growth of non-mycorrhizal plants. In a simple approximation the relative effectiveness was calculated to range from 1.46 to 15.57. Shoot P contents were increased by up to 25 times by A. laevis, significantly more than by the other two fungi. The further mycelial spread of this fungus is thought to have contributed to its relatively greater effect on plant P content.     

The first record of the non-indigenous signal crayfish <Emphasis Type="Italic">Pasifastacus leniusculus</Emphasis> in Norway

The non-indigenous signal crayfish Pasifastacus leniusculus was registered for the first time in Norway in October 2006. The location represents an isolated pond about 100 km in air line from the nearest known signal crayfish population in the neighbouring country Sweden without any connecting watercourses. The occurrence is therefore undoubtedly caused by human introduction. Molecular analyses confirmed that tested individuals from the signal crayfish population were carriers of the crayfish plague agent Aphanomyces astaci. Disease carrying signal crayfish represents a severe threat to the indigenous and endangered noble crayfish Astacus astacus. Norwegian authorities are currently considering actions for the eradication of the signal crayfish population.     

Impact of boron deficiency on Xenopus laevis: a summary of biological effects and potential biochemical roles

The toxicity of boron has been understood for many years. However, limited data currently exist concerning the nutritional essentiality of B in chordates. Results from an ongoing research program evaluating the nutritional essentiality of B in the South African clawed frog, Xenopus laevis, found that X. laevis fed a low-B diet in a low-B culture media produced a substantially higher number of necrotic eggs and fertilized embryos than frogs fed a boron-sufficient diet. Markedly decreased embryo cell counts at mid-blastula transition and an increased frequency of abnormal gastrulation were also noted in embryos from adult frogs fed the B-deficient diet. By 96 h of development, none of the larvae collected from the B-deficient adults and maintained in low-boron culture media developed normally. Reproductive effects associated with B deficiency in female Xenopus included ovary atrophy, oocyte necrosis, and incomplete oocyte maturation. In males, a decrease in testis weight and sperm count was noted. These studies suggest that these adverse effects resulting from B deficiency could be found during gametogenesis, gamete maturation embryonic development, and larval maturation. The studies also confirmed that B deficiency was capable of interrupting the X. laevis life cycle. Additional studies evaluating the role of B in the thyroid axis and the oocyte plasma membrane progesterone receptor provide the first line of direct evidence for a biochemical role of boron in X. laevis. Combined together, this research program provides firm evidence that B is nutritionally essential in X. laevis.