Mónica Mirta Steciow

Diversity, role in decomposition, and succession of zoosporic fungi and straminipiles on submerged decaying leaves in a woodland stream

Leaf litter is a very important primary source of energy in woodland streams. Decomposition of leaf litter is a process mediated by many groups of microorganisms which release extracellular enzymes for the degradation of complex macromolecules. In this process, true fungi and straminipiles are considered to be among the most active groups, more active than the bacteria, at least during the early stages of the process. Colonization increases the quality of the leaves as a food resource for detritivores. In this way, matter and energy enter detritus-based food chains. Previously, aquatic hyphomycetes were considered to be the major fungal group responsible for leaf litter decomposition. Although zoosporic fungi and straminipiles are known to colonize and decompose plant tissues in various environments, there is scant information on their roles in leaf decomposition. This study focuses on the communities of zoosporic fungi and straminipiles in a stream which are involved in the decomposition of leaves of two plant species, Ligustrum lucidum and Pouteria salicifolia, in the presence of other groups of fungi. A characteristic community dominated by Nowakowskiella elegans, Phytophthora sp., and Pythium sp. was found. Changes in the fungal community structure over time (succession) was observed: terrestrial mitosporic fungi appeared during the early stages, zoosporic fungi, straminipiles, and aquatic Hyphomycetes in early-to-intermediate stages, while representatives of the phylum Zygomycota were found at early and latest stages of the decomposition. These observations highlight the importance of zoosporic fungi and straminipiles in aquatic ecosystems.

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.

Potential distribution of Batrachochytrium dendrobatidis in Argentina: implications in amphibian conservation

Within the last two decades Batrachochytrium dendrobatidis (B.d.), the causative agent of chytridiomycosis, seems to have become a pandemic parasite, and is proposed as one of the more important causes of amphibian declines worldwide. In Argentina, the first report was in 2002 in Leptodactylus ocellatus. Since then, the fungus has expanded through different environments and species. In this study, we predict B.d. distribution in Argentina applying niche modelling based on reports of infected amphibians and environmental variables. The distribution hypothesis showed regions with highest suitability for B.d. including habitat types with (1) the most diverse amphibian fauna in Argentina such as the Paraná River Basin, (2) endangered species, such as north Patagonia and northwest Andean highlands, and (3) wide range of optimum precipitation and temperatures allowing development of B.d.

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.

Diversity of zoosporic true fungi and heterotrophic straminipiles in Las Canas stream (Buenos Aires, Argentina): assemblages colonizing baits

Zoosporic true fungi and heterotrophic straminipiles are phylogenetically unrelated groups of microorganisms playing similar ecological roles in food webs in fresh water ecosystems. As saprotrophs they are important decomposers of organic matter of animal and vegetal origin. However, there is still little research on most aspects of the ecology of these microorganisms. In this study the species composition of zoosporic true fungi (Blastocladiomycota and Chytridiomycota) and heterotrophic straminipiles (Hyphochytriomycota and Peronosporomycota), and their frequency, abundance and diversity on different types of baits were analyzed. Samples for characterizing the species composition were collected over a four-year period and for characterizing the structure of the assemblages at four dates during a one-year period. The relationship between some biological and environmental parameters were analysed. We expected that fluctuations in environmental factors during the year might lead to changes in the species composition and structure of the assemblages. Sixty-eight taxa were recovered with the baiting technique during the four-year period. The species composition was dependent primarily on the type of bait used. The structure of the assemblages also appeared to be more influenced by the type of baits available for colonization than by other environmental parameters. Even though the abundance of the taxa was associated with pH, nitrite, sulfate, soluble reactive phosphorous and dissolved oxygen concentrations. We did not find any differences in their richness, frequency, abundance and diversity during the year as expected.

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.

Relación entre el gen Rps 1k y la resistencia a Pythium ultimum y P. irregulare en soja

Em soja Pythium spp. causa apodrecimento de sementes, da raiz e “tombamento”. O objetivo deste estudo foi verificar a relacao do gene de resistencia Rps 1k de Phytophthora sojae com Pythium ultimum e P. irregulare. Quatro genotipos de soja foram semeados em solo inoculado ou nao com Pythium spp, dois deles com o gene Rps 1k (SE+1 e SE+2) e os outros dois sem ele (SE-1 e SE-2). Os genotipos SE-1 e SE-2 nao diferiram entre si, nao importa se eles foram inoculados ou nao, nem eram diferentes de SE + 2. Por outro lado, genotipos com Rps 1k diferiam uns dos outros, sendo inoculados ou nao. SE + 2 apresenta uma emergencia de 95% enquanto que a SE + 1 tinha 78.35% de emergencia, mas em ambos os casos a emergencia diminuiu quando foram inoculados, com 63.35% e 34.15% respectivamente. Nas condicoes analisadas o gene Rps 1k de resistencia a Ph. sojae nao mostrou aumento do numero de plântulas emergidas testados contra as especies de P. ultimum ou P. irregulare.

Batrachochytrium dendrobatidis infecting anurans in a protected area from Santa Fe Province, Argentina

Se reporta la presencia de Batrachochytrium dendrobatidis en Hypsiboas pulchellus del Parque Nacional Islas de Santa Fe