北京地区水霉科真菌季节性分布

本文报道北京地区水霉科(Saprolegniaceae)真菌季节性分布的调查、研究结果,发现影响水霉季节性分布的主要因素是水温的季节性变化。不同属、种具不同的季节性分布,而种的季节性分布与它们卵孢子的结构有关。     

Some species of saprolegniaceae collected from Gorakhpur,India

Summary Eleven species of Saprolegniaceae viz., Saprolegnia diclina, S. ferax, Isoachlya anisospora, Achlya dubia, A. proliferoides, A. diffusa, A. orion, A. prolifera, A. conspicua, Aphanomyces helicoides, and Leptolegnia sp. (sterile) collected from waters of Gorakhpur have been described.This forms part of a thesis accepted for the degree of Ph. D. in the University of Gorakhpur, Gorakhpur.     

Genetic comparison of water molds from embryos of amphibians Rana cascadae, Bufo boreas and Pseudacris regilla

Water molds that cause the disease saprolegniasis have been implicated in widespread mortality of amphibian embryos. However, because of the limitations of traditional identification methods, water mold species involved in die-offs or utilized in ecological studies often remain unidentified or identified only as Saprolegnia ferax. Furthermore, water mold taxonomy requires revision, so very distinct organisms may all be called S. ferax. Recent DNA-based studies indicate that the diversity of water molds infecting amphibian embryos is significantly higher than what was previously known, but these studies rely on culture methods, which may be biased towards taxa that grow best under laboratory conditions. In this study, total embryo-associated DNA was extracted from 3 amphibian species in a pond in central Washington, USA. The internal transcribed spacer (ITS) region of DNA was amplified with primers capable of amplifying a broad array of eukaryotic microorgansisms, and was used to construct clone libraries. Individual clones were sequenced and relationships among newly recovered sequences and previously studied taxa were analyzed using phylogenetics. These methods recovered several new taxa in association with amphibian embryos. Samples grouped into 11 distinct phylotypes with ITS sequence differences ranging from 4 to 28%. The water mold communities recovered differed among Rana cascadae, Bufo boreas, and Pseudacris regilla egg masses. Furthermore, the diversity of water molds increased as egg masses aged, and members comprising this diversity changed over time.     

Fungi isolated from cultured eggs, alevins and broodfish of brown trout in a hatchery affected by saprolegniosis

The aquatic fungi cultured from eggs, alevins and broodfish of brown trout Salmo trutta belonged to the genus Saprolegnia and were identified as S. diclina , S. australis , S. ferax , S. furcata , S. hypogyna , S. unispora and S. parasitica . The species obtained from infected eggs and alevins were different to those from infected fish. Several Saprolegnia species were isolated from eggs and alevins, whereas all the isolates obtained from broodfish were the pathogenic S. parasitica .     

Resistance of perch eggs to attack by aquatic fungi

In the distinctive gelatinous Perca fluviatilis egg mass, limited fungal growth by Aphanomyces and Saprolegnia spp. especially S. diclina , occurred within dead eggs but did not spread to adjacent live eggs. Perch eggs exposed to parasitic challenge by Saprolegnia parasitica , S. dieclina (type III) and S. ferax , under fluctuating temperature regimes replicating spring water temperatures, did not have significantly greater mortality than did unchallenged controls. The observations suggest that perch eggs have some anti-fungal properties which usually prevent the spread of fungus throughout the egg mass and that under normal spring temperatures there should be negligible ecological consequences of fungal infection in perch egg masses.     

Differences in susceptibility to Saprolegnia infections among embryonic stages of two anuran species

Many amphibians are known to suffer embryonic die-offs as a consequence of Saprolegnia infections; however, little is known about the action mechanisms of Saprolegnia and the host-pathogen relationships. In this study, we have isolated and characterized the species of Saprolegnia responsible for infections of embryos of natterjack toad (Bufo calamita) and Western spadefoot toad (Pelobates cultripes) in mountainous areas of Central Spain. We also assessed the influence of the developmental stage within the embryonic period on the susceptibility to the Saprolegnia species identified. Only one strain of Saprolegnia was isolated from B. calamita and identified as S. diclina. For P. cultripes, both S. diclina and S. ferax were identified. Healthy embryos of both amphibian species suffered increased mortality rates when exposed to the Saprolegnia strains isolated from individuals of the same population. Embryonic developmental stage was crucial in determining the sensitivity of embryos to Saprolegnia infection. The mortalities of P. cultripes and B. calamita embryos exposed at Gosner stages 15 (rotation) and 19 (heart beating) were almost total 72 h after challenge with Saprolegnia, while those exposed at stage 12 (late gastrula) showed no significant effects at that time. This is the first study to demonstrate the role of embryonic development on the sensitivity of amphibians to Saprolegnia.     

Evolution of spore release mechanisms in the saprolegniaceae (Oomycetes): evidence from a phylogenetic analysis of internal transcribed spacer sequences

Classical studies on spore release within the Saprolegniaceae (Oomycetes) led to the proposition that different mechanisms of sporangial emptying represent steps in an evolutionary transition series. We have reevaluated this idea in a phylogenetic framework using internal transcribed spacer sequences of four genera. These data were compared with the response to osmotic stress exhibited by each taxon. Saprolegnia emerges as the most basal genus, sister to Achlya, Thraustotheca, and Dictyuchus. Achlya and Thraustotheca are most closely related, while Dictyuchus appears to have evolved along a separate evolutionary lineage. The resulting phylogenetic framework is consistent with the idea that the mechanism of sporangial emptying exhibited by Saprolegnia represents the plesiomorphic condition from which the other mechanisms were derived independently. These alternative mechanisms of spore release may have resulted from a small number of mutations that inhibited axonemal development and altered the temporal and spatial expression of lytic enzymes that degrade the sporangial wall. Copyright 1998 Academic Press.     

黄颡鱼卵水霉病病原的分离鉴定及其无性繁殖特性

【目的】对黄颡鱼卵水霉病病原进行分离鉴定,并对其无性繁殖特性进行研究。【方法】采用传统方法从患水霉病的黄颡鱼卵上进行丝状真菌的分离,然后通过人工感染实验证实分离菌株的致病性,通过形态学观察和ITS rDNA序列分析对致病菌株进行鉴定,并进一步通过单因子法研究其无性繁殖特性。【结果】从患水霉病的黄颡鱼卵上分离了4株丝状真菌,经人工感染试验证实其中一株丝状真菌HP对黄颡鱼卵具有致病性,并进一步研究了其形态与无性繁殖特性,开展了ITS rDNA序列分析。实验结果表明,菌株HP菌丝为透明管状结构,中间无横隔,分枝较少;游动孢子囊多数呈棒状,游动孢子发育成熟后从孢子囊中释放出来,并迅速游离;能够产生第二孢孢子;新孢子囊以内层出的方式产生;藏卵器呈球形,与雄器同枝或异枝。菌株HP的ITS rDNA序列与GenBank基因库中水霉属菌株自然聚类,同源性高达99%,与多子水霉菌株Arg4S(GenBank登录号GQ119935)的亲缘关系最近。结合形态特征与ITS序列鉴定的结果,判定菌株HP为多子水霉(Saprolegnia ferax)。此外,菌株HP在5°C-35°C、pH 4-10范围内均能产生游动孢子,产生游动孢子的最适温度和pH分别为20°C和7,而且5-25 mg/L福尔马林和0.25 1.25 mg/L二硫氰基甲烷对菌株HP产生游动孢子具有明显的抑制作用。【结论】分离鉴定了黄颡鱼卵水霉病病原,并确定了其无性繁殖特性,可以作为该病防治用药的依据。     

Experimental transmission and pathogenicity of some zoosporic fungi toTilapia fish

Seventeen fungal species belong to six genera were recovered from the four organs ofTilapia fish and the most common wereSaprolegnia ferax, S. diclina, Achlya dubia, A. americana, A. racemosa andA. flagellata, Dictyuchus sterile,Pythium undulatum andAphanomyces sp. Severe infection followed by death of all fish was incited byS. parasitica andS. ferax through experiment I. 30–70% ofT. nilotica andT. galileae were killed through experiment II byS. parasitica andS. ferax. T. galileae was more susceptible to fungal infection thanT. nilotica.     

Basic nuclear proteins in the aquatic fungus Achlya ambisexualis.

The complement of basic chromosomal proteins in the aquatic fungus Achlya ambisexualis has been characterized. Achlya nuclei contain proteins with electrophoretic mobilities on acetic acid/urea and dodecyl sulphate polyacrylamide gels which are comparable to rabbit kidney histones H3, H4 and H2A. In contrast, the behavior of putative H2B and H1 proteins from Achlya showed greater analogy on acid/urea gels to higher plant histones. A closely related water fungus Saprolegnia ferax contained basic nuclear proteins which were very similar to those of Achlya.     

Studies on species of fungi associated with mycotic infections of fish in a Nigerian freshwater fish pond

A survey was carried out on the species of fungi associated with mycotic infections of fish in a Nigerian freshwater fish pond. A total of 24 fungal species belonging to 6 genera of aquatic phycomycete were isolated from the infected fishes. Achlya racemosa, Aphanomyces laevis, Dictyuchus sterile, Saprolegnia ferax, S. litoralis and S. parasitica had 100% frequency of occurrence amongst the infected fishes. There were similarities in the species of fungi isolated from the infected fishes in the fish pond and those isolated from the hatchery. Of the infected fishes, Clarias lazera had the highest number of fungal isolates. It was followed by Tilapia zilli, then by Chanos chanos, Ethmalosa fimbriata and finally by Cyprinus carpio. The implications of the results obtained on the development of fish farming in Nigeria are discussed.     

Five Serbian reservoirs contain different fungal propagules

This paper presents results of a mycological survey conducted in five large reservoirs in Serbia (Sjenica, Barje, Garasi, Meduvrsje and Ovcar-Kablar) that have different hydrobiological and production characteristics. The sampling was conducted in March, June, August and October 2002. Quantitative analysis of fungal communities showed that the average number of colony-forming units in these reservoirs was 1966-5682/L of water. The highest number of CFUs was found in the alpha-mesosaprobic (Class III) Ovcar-Kablar Reservoir and the lowest was in the oligosaprobic (Class I) Sjenica Reservoir. CFUs were higher in samples taken near lake bottoms and in littoral zones rich with macrovegetation than in the middle depths. In these reservoirs 48 species were identified from 720 isolates. The dominant genera were Penicillium, Aspergillus, Cladosporium, Fusarium, Rhizopus, Mucor, Phoma and Verticillium. The autochthonous aquatic fungal community comprised these species: Achlya americana, A. diffusa, A. racemosa, Dictyuchus sterile, Isoachlya toruloides, Leptomitus lacteus, Pythium ultimum, Saprolegnia ferax, S. hypogyna and S. monica. My results indicate that aquatic fungi on the whole are better represented in lakes with a higher trophic status.     

Re-evaluation of the enigmatic species complex Saprolegnia diclina-Saprolegnia parasitica based on morphological, physiological and molecular data

The phylogenetic relationships among isolates of the Saprolegnia diclina-Saprolegnia parasitica complex were investigated based on ITS rDNA sequences, and correlated with morphological and physiological characters. The isolates studied belong to five phylogenetically separate clades. The majority of presumed parasitic isolates, mostly isolated from fish lesions, fell within a clade that comprises isolates which has been variously named as S. diclina Type 1, S. parasitica, Saprolegnia salmonis or just as unnamed Saprolegnia sp. Presence of bundles of long-hooked hairs on secondary cysts, high frequency of retracted germination, and oogonia production at 7 degrees C (when occurring) were characteristic of this clade. A single isolate identified as S. diclina Type 2 clustered in a clade along with Saprolegnia ferax isolates. The isolates identified as S. diclina s. str. (S. diclina Type 3) distributed in two clades and appeared closely related to Saprolegnia multispora and to a number of Chilean isolates identified as Saprolegnia australis. The ITS sequences of clade I were almost identical even though the isolates were of diverse geographical origins and showed physiological and morphological differences and variations in their pathogenicity. This suggest these species reproduces clonally even in apparently sexually competent isolates. Adaptation to parasitism in Saprolegnia might have occurred at spore level by the development of long-hooked hairs to facilitate host attachment and selection of a retracting germination. The use of the name S. parasitica should be assigned to isolates of clade I that contained isolates forming cysts with bundles of long-hooked hairs.     

Molecular identification of a bronopol tolerant strain of Saprolegnia australis causing egg and fry mortality in farmed brown trout, Salmo trutta

Some species of the genus Saprolegnia, such as Saprolegnia diclina and Saprolegnia ferax are responsible for devastating infections on salmonid eggs. Members of this group cause saprolegniasis, a disease resulting in considerable economic losses in aquaculture. Although both S. diclina and S. ferax have received much attention, the role of other Saprolegnia species in infecting fish eggs is less known. For this purpose, we have investigated the aetiology of chronic egg mortality events occurring in farmed brown trout, Salmo trutta. A total of 48 isolates were obtained from eggs with signs of infection as well as from water samples. A molecular analysis based on nrDNA internal transcribed spacer (ITS) operational taxonomic units indicated that the majority of the isolates correspond to Saprolegnia australis. All isolates of S. australis exhibited the same random amplified polymorphic DNA (RAPD) band patterns suggesting that a single strain is implicated in egg infections. The isolates followed Koch postulates using trout eggs and fry. Under standard concentrations of bronopol commonly used in farms, these isolates could grow, but not sporulate. However, both growth and sporulation were recovered when treatment was removed. This study shows that S. australis can infect and kill salmon eggs, and helps in defining oomycetes core pathogens.     

Effects of nitrate and the pathogenic water mold Saprolegnia on survival of amphibian larvae

We tested for a synergism between nitrate and Saprolegnia, a pathogenic water mold, using larvae of 3 amphibian species: Ambystoma gracile (northwestern salamander), Hyla regilla (Pacific treefrog) and Rana aurora (red-legged frog). Each species was tested separately, using a 3 x 2 fully factorial experiment with 3 nitrate treatments (none, low and high) and 2 Saprolegnia treatments (Saprolegnia and control). Survival of H. regilla was not affected significantly by either experimental factor. In contrast, survival of R. aurora was affected by a less-than-additive interaction between Saprolegnia and nitrate. Survival of R. aurora was significantly lower in the Saprolegnia compared to the control treatment when nitrate was not added, but there was no significant difference in survival between Saprolegnia and control treatments in the low and high nitrate treatments, consistent with increased nitrate preventing Saprolegnia from causing mortality of R. aurora. Survival of A. gracile followed a similar pattern, but the difference between Saprolegnia and control treatments when nitrate was not added was not significant, nor was the nitrate x Saprolegnia interaction. Our study suggests that Saprolegnia can cause mortality in amphibian larvae, that there are interspecific differences in susceptibility and that the effects of Saprolegnia on amphibians are context-dependent.     

The occurrence of Achlya recurva (Saprolegniales, Oomycetes) in hydrocarbon-polluted soil from Argentina

Saprolegniaceae are ubiquitous filamentous water molds. They occur as saprotrophs or parasitic on aquatic and terrestial plants and on aquatic animals, and a number of interesting fungi belonging to the Saprolegniaceae have been isolated from the soil. In the course of an investigation of the water molds in Argentina, an unusual species of Achlya was isolated once from soil collections. Brassica napus seeds were used as bait as well as for the maintenance of this fungus in gross water cultures. Achlya recurva Cornu (Saprolegniales, Oomycetes), was isolated from a hydrocarbon-polluted soil (crude oil) in the neighborhood of an oil tank from a distillery (Ensenada, Buenos Aires Province). This species is reported, described and illustrated for the first time from Argentina. Remarks on the habitat are also made because it was never found in polluted areas.     

Mycoflora of mangroves of red sea in Egypt

Nine species in addition to two unidentified species belonging to 8 genera of zoosporic fungi were recovered from 12 mangrove water and mud samples on hemp and sesame seeds,Pinus poolen grains and onion skin as baits at 22°C.Saprolegnia ferax, S. furcata andPhlyctochytrium sp. were recovered only from water samples;Allomyces arbuscula, Pythium aphanidermatum, P. thalasium andThraustochytrium roseum were recovered only from mud samples.     

Plasma membrane-adjacent actin filaments, but not microtubules, are essential for both polarization and hyphal tip morphogenesis in Saprolegnia ferax and Neurospora crassa

The organization and roles of F-actin and microtubules in the maintenance and initiation of hyphal tip growth have been analyzed in Saprolegnia ferax and Neurospora crassa. In hyphae of both species, the apex is depleted of microtubules relative to subapical regions and near-normal morphogenesis occurs in concentrations of nocodazole or MBC which remove microtubules, slow growth, and disrupt nuclear positioning. In contrast, each species contains characteristic tip-high arrays of plasma membrane-adjacent F-actin, whose organization is largely unaltered by the loss of microtubules but disruption of which by latrunculin B disrupts tip morphology. Hyphal initiation and subsequent normal morphogenesis from protoplasts of both species and spores of S. ferax are independent of microtubules, but at least in S. ferax obligatorily involve the formation of F-actin caps adjacent to the hyphal tip plasma membrane. These observations indicate an obligatory role for F-actin in hyphal polarization and tip morphogenesis and only an indirect role for microtubules.     

Symbiotic green algae in eggs of Hynobius nigrescens,an amphibian endemic to Japan

The egg capsules of some amphibians' eggs are known to become green colored before hatching. This is due to the increase of green symbionts in the egg capsule surrounding the embryo. The green symbionts in North American amphibian eggs were reported to be unicellular green algae in the Oophila‐clade of Volvocales, Chlorophyceae. However, it remains unclear whether this is also the case in other parts of the world. In this study, we analyzed the green symbionts in green‐colored eggs of Hynobius nigrescens, an amphibian endemic to Japan, obtained from five distinct locations. Microscopic observations revealed that the green symbionts were similar in appearance to Oophila amblystomatis, which was reported in some amphibian eggs in North America, in which non‐motile cells of the algae had thick cell walls with reticulate protuberances. PCR‐DGGE followed by phylogenetic analyses of partial 18S rRNA sequences revealed that the symbionts from the five locations were identical and most likely unialgal in each egg capsule. They formed an independent subclade within the Oophila‐clade, indicating that H. nigrescens has a unique symbiont. Our data are consistent with the previous report on North American amphibian eggs and support the specific symbiotic relationships between Oophila‐clade symbionts and the eggs of amphibians. This is the first report on the specific symbiont‐and‐host association between an Oophila‐clade symbiont and an amphibian outside of North America. We also discuss several possibilities regarding the origin of green symbionts (vertical transmission or invasion) on the basis of the discovery and detailed observation of H. nigrescens eggs without any green symbionts.