Oomycete parasites in freshwater copepods of Patagonia: effects on survival and recruitment.

Copepods are hosts to various oomycete parasite species, but the effects of pathogens on copepod populations have rarely been studied. This study aimed to characterize oomycete infection in the freshwater copepod Parabroteas sarsi in a temporary pond in Patagonia (Argentina). A complete hydroperiod was monitored, evaluating environmental variables as influencing factors in the oomycete infections. Laboratory experiments were performed to evaluate the susceptibility of infected copepods to consumption by predators. Although 5 species of copepods were present in the pond, only ovigerous P. sarsi females were parasitized by oomycetes. Two species of oomycetes were always found together: Aphanomyces ovidestruens and Pythium flevoense. Infections were detected at water temperatures >20°C, with a positive relationship between temperature and parasite prevalence. Infection occurred after a decrease in large filter-feeder densities. The pathogens were not lethal to P. sarsi females in the short-term, but did produce mortality of entire egg sacs, thus negatively impacting subsequent recruitment. Mean prevalence of infection in females was 53%, reaching 83% in December. Females have the capacity to release an infected egg sac and generate a new one in a few days. This infection does not affect the susceptibility of P. sarsi to the predator Notonecta vereertbruggheni. The decrease in female abundance registered towards the end of the hydroperiod could be related to a combination of factors that may have a differential effect on female survival, such as increasing temperature, the energy cost of egg sac development and carrying and oomycete infection.

Multiple barcode assessment within the Saprolegnia-Achlya clade (Saprolegniales, Oomycota, Straminipila) brings order in a neglected group of pathogens.

The Saprolegnia-Achlya clade comprises species of major environmental and economic importance due to their negative impact on aquaculture and aquatic ecosystems by threatening fishes, amphibians, and crustaceans. However, their taxonomy and phylogenetic relationships remain unresolved and suffer from many inconsistencies, which is a major obstacle to the widespread application of molecular barcoding to identify pathogenic strains with quarantine implications. We assessed phylogenetic relationships of major genera using three commonly used markers (ITS, SSU rRNA, and LSU rRNA). A consensus tree of the three genes provided support for nine clades encompassing eleven documented genera and a new clade (SAP1) that has not been described morphologically. In the course of this study, we isolated a new species, Newbya dichotoma sp. nov., which provided the only culture available for this genus. In parallel, we attempted to summarize the evolution of traits in the different genera, but their successive reversals rendered the inference of ancestral states impossible. This highlights even more the importance of a bar-coding strategy for saprolegniacean parasite detection and monitoring.

Incipient loss of flagella in the genus Geolegnia: the emergence of a new clade within Leptolegnia?

The genus Geolegnia represents a poorly documented group of saprolegnialean oomycetes isolated from soils as free-living organisms. Although it is morphologically similar to the facultative parasitic genus Leptolegnia, Geolegnia presents the uncommon property of having lost a flagellate stage in its lifecycle. Based on ITS and large subunit (LSU) rRNA sequence data, we show Geolegnia to be basal to Leptolegnia, and also introduce Geolegnia helicoides sp. nov. Using sequence data of Leptolegnia available in GenBank, supplemented by data derived from culture collections, we show that Geolegnia is nested within Leptolegnia, a genus characterised by its "conventional" biflagellate life cycle. The emergence of Geolegnia is therefore seen as a recent event, and we suggest here an evolutionary context where this loss might have been advantageous. Based on this study, Leptolegnia remains paraphyletic, awaiting the redefinition of genera in this complex.

Frequency, abundance and distribution of zoosporic organisms from Las Cañas stream (Buenos Aires, Argentina).

Zoosporic organisms are common inhabitants of aquatic environments; however there are few ecological studies made for Argentinean streams. In this contribution the taxonomic composition of zoosporic organisms from a stream and their abundance, frequency and diversity on cellulosic baits were analyzed. Samples of water and floating organic matter (vegetable debris) were taken at four dates and different environmental variables (temperature, dissolved oxygen and nutrient concentrations) were measured. Twenty-one taxa were recovered with the baiting technique. Physicochemical fluctuations affected the structure of the studied community; in spring the greatest species richness was related to high nutrient levels whereas in winter the greatest abundance and diversity was related to low water temperature, nutrient levels and well oxygenated conditions. aquatic environment,

Achlya spiralis, a new aquatic oomycete with bent oogonial stalks, isolated from the Burgundian region of France.

Achlya spiralis sp. nov. was isolated from water samples collected in the river Tille in the Burgundian region of France. The new oomycete is described, illustrated and compared with related species of the genus Achlya. It is characterized by the presence of smooth-walled oogonia that are usually borne on bent or twisted oogonial stalks; mainly monoclinous, androgynous and diclinous antheridial branches and eccentric oospores which generally do not mature or mature after a long period of time. The internal transcribed spacer (ITS) region of its rRNA is comprised of 671 bases. The taxonomic description of this new species, its comparison with related oomycetes and the sequence of the ITS region of its rRNA are discussed here.

Saprolegnia bulbosa sp. nov. isolated from an Argentine stream: taxonomy and comparison with related species.

Saprolegnia bulbosa sp. nov. was isolated from floating and decaying twigs and leaves in El Gato stream, Partido de La Plata, Buenos Aires Province, Argentina. The distinctive characteristics of S. bulbosa are the product of smooth oogonia and predominantly contorted monoclinous, androgynous and diclinous antheridia. The oogonial stalks are usually bent, curved or once coiled; oospores are subcentric, (1) 2-15 (45) per oogonium and are variable in size. Taxonomical description of this new species, its comparison with related oomycetes of the genus and the nucleotide sequences of the internal transcribed region (spacers ITS1, ITS2 and the gene 5.8S) of its rRNA gene are given here.

Chytrid fungus parasitizing the wild amphibian Leptodactylus ocellatus (Anura: Leptodactylidae) in Argentina.

The present contribution is the first report of parasitosis by a chytrid fungus in wild anuran amphibians in Argentina, as well as the first case of amphibian mortality documented to date in Argentina. We report the presence of the chytrid fungus in dead adult Leptodactylus ocellatus. It has been suggested that chytridiomycosis is the main cause of death in several amphibian populations worldwide. Our study demonstrates that chytridiomycosis afflicts L. ocellatus, a common widespread amphibian species, and is the first report of chytridiomycosis in the Argentinian lowlands. The occurrence at this latitude would indicate an extended distribution of this fungus in wildlife populations. It is also the first report of amphibian mortality due to chytrid fungus in our country. It is noteworthy that the site of collection is situated very close to sea level in a temperate climate zone and that this represents the southern most record for South American wild amphibians.

Saprolegnia multispora, a new oomycete isolated from water samples taken in a river in the Burgundian region of France.

Saprolegnia multispora is described from water and floating organic matter taken in the Tille River, in the Burgundian region of France. The new species is illustrated and compared with other species of the genus. Distinguishing characteristics of S. multispora are the production of smooth-walled oogonia containing many subcentric oospores which are (1-) 11-70 (-100) per oogonium. The antheridial branches supplying the oogonia are predominantly diclinous, but at times these may be monoclinous and androgynous. Morphological features of the oomycete and the sequence of the ITS region of its rDNA as well as their comparison with related species are discussed in this article.

Saprolegnia oliviae sp. nov. isolated from an Argentine river (Tierra del Fuego Province, Argentina).

Saprolegnia oliviae sp. nov. is described from litter (floating dead twigs, leaves and roots) in the Olivia River, Ushuaia Department, Tierra del Fuego Province (Argentina). The new species is illustrated and compared with other species of the genus. Distinguishing characteristics of S. oliviae are the production of smooth oogonia (with some lateral or terminal projections) and the absence of antheridial branches on the majority of the oogonia, but when present, they are mostly diclinous, at times oogonia are supplied with androgynous and monoclinous antheridial branches. The oogonial stalks are predominantly short and straight or long and bent, curved or many times coiled; oospores are distinctive subcentric, (1-) 15-50 (-70) per oogonium. Morphological details of the new species and its comparison with other described species are discussed here.

A new species of Brevilegnia (Saprolegniales, Straminipila) from Buenos Aires Province, Argentina.

Brevilegnia ensenadensis sp. nov. is described from litter (floating twigs, leaves, and roots) in a man-made, polluted channel near a petroleum refinery, in Buenos Aires Province, Argentina. The species is illustrated and compared with other species of the genus; it can be identified by the preponderance of smooth or papillate oogonia, with a distinctive irregular inner wall, borne in bent or coiled oogonial stalks, which are terminal, lateral or of the intercalary position. The oogonia often are irregular in shape, and the oospheres mostly are immature. The single oospore is eccentric inside the great oogonia, and the species develops mainly diclinous antheridial branches and has fewer monoclinous and androgynous ones.

A. robusta sp. nov., a new species of Achlya (Saprolegniales, Straminipila) from a polluted Argentine channel.

Achlya robusta sp. nov. was found on litter (floating twigs, leaves, and roots) in an artificial polluted channel, near a petroleum refinery, in Buenos Aires province, Argentina. The species is described, illustrated and compared with other species of the genus. A. robusta produces mainly smooth and papillate, tuberculate or bullate oogonia and monoclinous antheridial branches. It develops spherical and subglobose oogonia, with the oogonial wall yellowish and containing mainly immature oospheres. The oospores are eccentric and ranging from (1) 4-17 (30) per oogonium.

Análisis cuantitativo y cualitativo de hongos zoosporicos de la laguna Vitel y tributarios (prov. Buenos Aires, Argentina) / Quantitaive and qualitative analysis of zoosporic fungi from lagoon and tributaries (prov. Buenos Aires, Argentina)

Durante el año 1993-4, mediante el análisis mensual de muestras de agua y de materia orgánica flotante, se realizó un estudio cuanti-cualitativo de los hongos zoospóricos (oomycetes, chytridiomycetes) presentes en la laguna Vitel y sus tributarios (chascomús, de la provincia de Buenos Aires). Utilizándo anzuelos vegetales (semillas de cannabis sativa y brassica sp.), se aislaron 31 especies de hongos zoospóricos, de los cuales 16 son citadas por primera vez para Argentina. El análisis cuantitativo de sus propágulos totales por litro, determinó un mayor contenido en los períodos estacionales de otoño y primavera.

Micobiota de la Laguna Vital y tributarios (Chascomús, Argentina)

Después de realizar un estudio cuali-cuantitativo de la miccobiota en la Laguna Vitel y tributarios fueron obtenidas 28 especies de hongos zoospóricos, a partir de muestras de agua y de materia orgánica flotante, a lo largo de 1 año. Se calculó la abundancia y frecuencia relativa de las especies pertenecientes a la Cl. Oomycetes y Chytridiomycetes (S.D.Mastigomycotina)

Actividad enzimática de algunas saprolegniales, oomycetes / Enzymatic activity of some saprolegniales, oomycetes

Se ensayó la actividad enzimática de algunas Saprolegniales (Achlya americana, A. apiculata, A. oligacantha, A. polyandra, A. prolifera, Dictyuchus monosporus, Isoachlyatouroloides, Saprolegnia diclina y S. parasitica), en distintos medios sólidos. Estas especies fueron aisladas de materia orgánica flotante, en Río Santiago (Pdo. Ensenada, Provincia de Buenos Aires, Argentina), y se demostró que poseen actividad enzimática, in vitro, para la descomposición de pectina, celulosa, hemicelulosa, lignina y almidón

Utilización de hidrocarburos por oomycetes I: achlya polyandra Hildebrand / Hidrocarbons utilization by oomycetes I: achlya polyandra Hildebrand

Se ensayó el crecimiento de Achlya polyandra usándose como fuente carbonada: heptano, benceno, xileno, tolueno, nafta común, gas oil y kerosene. Esta especie mostró abundante crecimiento en las dos mezclas hidrocarbonadas (combustibles): gas oil y kerosene; en cambio, fue limitado en tolueno, benceno, xileno y nafta común, no registrando crecimiento en heptano