Carlos G. Vélez

Ultrastructural and molecular analyses of Rhizophydiales (Chytridiomycota) isolates from North America and Argentina

The Rhizophydiales is the most recently circumscribed order in the Chytridiomycota. Past studies focused on soil chytrids from North America and Australia to determine the range of diversity within this clade of chytrids and established three families (Rhizophydiaceae, Terramycetaceae, and Kappamycetaceae) in the new order. Although Rhizophydiales contains seemingly simple chytrids morphologically, analyses of ribosomal gene sequences and zoospore characters have demonstrated unexpected genetic and ultrastructural diversity, highlighting the need for broader habitat and geographic sampling to reveal the actual diversity within this new order. To enlarge our sampling, in this study we investigated 38 newly cultured chytrids collected from aquatic habitats in Argentina, a territory under-explored for chytrid diversity. From analyses of thallus morphology, zoospore ultrastructure, and 28S and ITS1-5.8S-ITS2 ribosomal gene sequences, we expand the concept of Rhizophydiales, describing seven new families (Alphamycetaceae, Angulomycetaceae, Aquamycetaceae, Globomycetaceae, Gorgonomycetaceae, Pateramycetaceae, and Protrudomycetaceae) and eight new genera (Alphamyces, Angulomyces, Aquamyces, Globomyces, Urceomyces, Gorgonomyces, Pateramyces, and Protrudomyces). Results of this study underscore that even more extensive sampling from varied habitats and geographies is needed to adequately ascertain the diversity of chytrids in the Rhizophydiales.

Molecular phylogenetic and zoospore ultrastructural analyses of Chytridium olla establish the limits of a monophyletic Chytridiales

Chytridium olla A. Braun, the first described chytrid and an obligate algal parasite, is the type for the genus and thus the foundation of family Chytridiaceae, order Chytridiales, class Chytridiomycetes and phylum Chytridiomycota. Chytridium olla was isolated in coculture with its host, Oedogonium capilliforme. DNA was extracted from the coculture, and 18S, 28S and ITS1-5.8S-ITS2 rDNA were amplified with universal fungal primers. Free swimming zoospores and zoospores in mature sporangia were examined with electron microscopy. Molecular analyses placed C. olla in a clade in Chytridiales with isolates of Chytridium lagenaria and Phlyctochytrium planicorne. Ultrastructural analysis revealed C. olla to have a Group II-type zoospore, previously described for Chytridium lagenaria and Phlyctochytrium planicorne. On the basis of zoospore ultrastructure, family Chytridiaceae is emended to include the type of Chytridium and other species with a Group II-type zoospore, and the new family Chytriomycetaceae is delineated to include members of Chytridiales with a Group I-type zoospore.

Three new genera in Chytridiales from aquatic habitats in Argentina

Sampling for chytrids in a variety of habitats has resulted in pure cultures that when analyzed have yielded hypotheses of relationships based on molecular and zoospore ultrastructural markers. To extend our understanding of diversity of Chytridiales in eastern Argentina and USA, we isolated and examined the morphology, ultrastructure and 28S and ITS1-5.8S-ITS2 rDNA sequences of numerous chytrids from aquatic habitats from these two regions. Three family-level lineages (Chytridiaceae, Chytriomycetaceae, family incertae sedis) are represented in our molecular phylogeny, and three new genera (Avachytrium, Odontochytrium in Chytriomycetaceae, Delfinachytrium in family incertae sedis) are described. These findings of new genera and species emphasize the potential for discovery of additional diversity.

New taxa are delineated in Alphamycetaceae (Rhizophydiales, Chytridiomycota)

Zoospore ultrastructure and molecular phylogenetic analyses are revealing unrealized diversity among zoosporic fungi. The taxonomically challenging morphogenus Rhizophydium Schenk, with more than 220 described taxa, is now conceptually an order (Rhizophydiales Letcher) containing 10 families, 15 genera, and numerous undescribed isolates. Each family is a monophyletic group within which a unique suite of ultrastructural character states is found in the zoospore. Until now, the family Alphamycetaceae Letcher contained a single genus, Alphamyces Letcher. Herein we analyze zoospore ultrastructure and LSU and ITS1-5.8S-ITS2 rRNA gene sequences of 11 isolates in Alphamycetaceae from Australia and North, Central, and South America, and delineate two new genera, Betamyces and Gammamyces, each with a distinct zoospore subtype within the family. This work provides a blueprint for additional taxonomic revisions in Rhizophydiales, and the results indicate that sampling from diverse habitats and localities is necessary to reveal diversity among chytrids in Rhizophydiales.

Vitreochlamys primaverae (Volvocales, Chlorophyceae): A new green flagellate from the Antarctic Peninsula

The genus Vitreochlamys Batko comprises green flagellates with a swol- len cell wall, closely related to the matrices of the multicellular Volvocales and Tetrasporales. The first Antarctic record of this genus consisted of a population in- habiting a small coastal pond in front of Argentinean Primavera station, which did not fit into any known species. This study deals with the taxonomic description of this population under Vitreochlamys primaverae sp. nov., and the ecological charac- terization of its type environment. The erection of this new species is sustained by its comparison with the three most similar species (V. aulata (Pascher) Batko, V. nekrassovii ( korshikov) Nakazawa and V. gloeocystiformis (Dill) Nakazawa) using a number of reliable morphological diacritic features, as well as by its note- worthy biogeographical insulation, adaptation to extreme environmental condi- tions and poor low-range dispersion ability, probably on account of its particular environmental requirements.

Live observations on Myzocytium megastomum (Lagenidiales), parasitizing a green alga, Rhizoclonium sp. (Siphonocladales)

Myzocytium megastomum is described for the first time for Argentina. The present study is based on a natural population kept under laboratory conditions. The morphology of mature sporangia, and the formation and liberation of zoospores are described in detail. The extrasporangial nature of zoosporogenesis is recorded and documented. Possible sources of variations in the length of the sporangial discharge tube are discussed. Resumen: Myzocytium megastomum se describe por primera vez para la Argentina. El presente estudio esta basado en material de una poblacio n natural mantenida viva en laboratorio. Se pone especial atencio n en la morfologi a de los esporangios maduros, y la formacio n y liberacio n de las zoosporas. La naturaleza extraesporangial de la zoosporoge nesis es registrada y documentada. Se discuten las posibles causas de la variabilidad en la longitud del tubo de descarga de los esporangios.