Zoosporic fungi of Oceania

Summary In a further study of the zoosporic fungi of Oceania three new species of Rhizophydium, R. rarotonganensis, R. angulosum, and R. condylosum were isolated on various substrata from soil. Rhizophydium rarotonganensis is a parasite of Nowakowskiella profusa and causes marked local hypertrophy of the rhizomycelium. Rhizophydium angulosum occured on bleached corn leaves and pollen grains and is characterized by predominantly angular sporangia with bush-like, finely branched rhizoids, and small zoospores. It differs from R. subangulosum by its saprophytic nature, inability to infect blue-green and green algae, and its ability to grow in axenic culture on synthetic media. Rhizophydium condylosum is keratinophilic and develops in great abundance on human hair, snake skin and other keratinic substrata. It is characterized primarily by spherical to ovoid sporangia with 1 to 30 exit pepillae which give them a knobby appearance.This study has been supported by a grant from the National Science Foundation, Washington, D.C.     

Beschreibung neuer Arten der Gattung Chytriomyces und einiger seltener niederer Phycomyceten

Zusammenfassung Es werden 4 neue, zur Gattung Chytriomyces gehörende Arten und 16 nicht sicher bestimmbare Formen von Rhizophydium, Phlyctochytrium, Rhizophlyctis, Chytridium, Hyphochytrium, Monoblepharis und Saprolegniaceen beschrieben.     

Notiz über das Vorkommen niederer Erdphycomyceten in der Antarktis

Zusammenfassung Aus fünf antarktischen Bodenproben von 60°45, 62°14 und 63°24 südlicher Breite wurden in 92 Ansätzen drei niedere Phycomyceten herausgeködert, nämlich Rhizophydium utriculare, Rhizophydium sphaerotheca und Hyphochytrium cf. catenoides. Sie alle sind auch von Standorten mit milderem Klima bekannt und Kosmopoliten.     

Monocentric fungi on species of rhizosolenia from saline habitats

Summary Eight monocentric fungi are reported in two provisionally identified species ofRhizosolenia from sea-water. Only two species are assigned specific names. These areRhizophydium planktonicum Canter andR. fragilariae Canter. A fungus with depressed-globose sporangia is included as a form ofR. fragilariae. Two unidentified species ofChytridium are reported. A fungus tentatively assigned toZygorhizidium and a form provisionally assigned toPetersenia are also reported and described insofar as their characteristics are known.     

Über klein- und großsporige Sporangien bei Phlyctochytrium palustre Gaertner und Rhizophydium racemosum Gaertner

Zusammenfassung Phlyctochytrium palustre Gaertner und Rhizophydium racemosum Gaertner bilden unter noch nicht näher analysierten Bedingungen zwei verschiedene Sporangientypen aus, die sich in ihrer Gestalt nur wenig oder gar nicht voneinander unterscheiden. Typ 1 enthält aber 3–4 (P. palustre) bzw. 2–2,5 (R. racemosum) große Zoosporen mit kleinem Globul, Typ 2 dagengen etwa doppelt so große, besonders lipoidreiche Zoosporen, die bei P. palustre immer begeißelt sind und zu normalen kleinsporigen Pflanzen heranwachsen. Bei Rhizophydium racemosum sind anscheinend zwei Entwicklungswege möglich: Die lipoidreichen Sporangiosporen werden entweder frei und wandeln sich dann in Zwergsporangien um, oder sie bleiben im Sporangium liegen und werden zu Dauersporen, die nach einer Ruheperiode mit einem Sporangium auskeimen. Es wird auf parallele Entwicklungsverläufe bei den Synchytriaceen hingewiesen.     

Observations of the heliozoean genera Pinaciophora and Acanthocystis (Heiliozoea,Sarcodina, Protozoa) from Ellis Fjord,Antarctica

Summary The heliozoeans Pinaciophora denticulata Thomsen, Acanthocystis perpusilla Petersen et Hansen, Acanthocystis turfacea Carter and Acanthocystis sp., collected from a marine location in Ellis Fjord, Antarctica and grown in saline culture, are pictured by scanning and transmission electron microscopy. P. denticulata has been reported from cold marine localities elsewhere in the world, but marine reports of Acanthocystis are rare, and both A. perpusilla and A. turfacea have been reported previously only from fresh waters.     

Studies of Aquatic Fungi. XVIII. Aquatic Fungi in Lake S̀niardwy and Eighteen Neighbouring Lakes

The work was undertaken to investigate the mycoflora of Lake S̀niardwy and eighteen adjacent lakes. Samples of water were collected once a month (1984-1987) for hydrochemical analysis and studies of the fungi content. Forty species of fungi were found in lake S̀niardwy and 60 in other lakes. The following fungi unknown from Poland were found in these lakes: Olpidium endogenum, Olpidium granulatum, Dictyomorpha dioica, Phlyctochytrium aureliae, Rhizophydium planktonicum, Zygorhizidium melosirae, Cladochytrium polystomum, Blastocladia rostrata, Olpidiopsis achlyae, Olpidiopsis pythii, Lagenidium rabenhorstii, Pythiella vernalis, Achlya rodrigueziana, Anguillospora gigantea, Dimorphospora foliicola and Mycocentrospora aquatica.     

The Effect of Light and Darkness Upon Infection of Asterionella formosa Hassall by the Chytrid Rhizophydium planktonicum Canter emend

Observations, both experimental and microscopic, indicate thatzoospores of Rhizophydium planktonicum Canter emend., can remainalive, but rarely become adherent upon cells of Asterionellaformosa Hassall under conditions of very low light or in completedarkness. The behaviour patterns of zoospores towards host cells underdarkened conditions were compared with those which took placeunder well illuminated conditions leading to the settlementof zoospores on host cells. The differences noted may help toexplain the lack of zoospores found upon inadequately illuminateddiatom cells. Some evidence suggests that young zoospores lack the abilityto adhere to host cells. After the encystment of zoospores uponAsterionella cells in the light, their further growth and developmentcan continue in darkness. Rhizophydium planktonicum Canter emend., Asterionella formosa Hassall, chytrid, diatom, infra-red illumination, zoospore     

Phylogenetic Position of Parasitic Chytrids on Diatoms: Characterization of a Novel Clade in Chytridiomycota

Chytrids are true fungi that reproduce with posteriorly uniflagellate zoospores. In the last decade, environmental DNA surveys revealed a large number of uncultured chytrids as well as undescribed order‐level novel clades in Chytridiomycota. Although many species have been morphologically described, only some DNA sequence data of parasitic chytrids are available from the database. We herein discuss five cultures of parasitic chytrids on diatoms Aulacoseira spp. and Asterionella formosa. In order to identify the chytrids examined, thallus morphologies were observed using light microscopy. We also conducted a phylogenetic analysis using 18S, 5.8S, and 28S rDNA sequences to obtain their phylogenetic positions. Based on their morphological characteristics, two cultures parasitic on As. formosa were identified as Rhizophydium planktonicum and Zygorhizidium planktonicum. The other three cultures infecting Aulacoseira spp. (two on Aulacoseira ambigua and the other on Aulacoseira granulata) were regarded as Zygorhizidium aff. melosirae. The results of the molecular phylogenetic analysis revealed that R. planktonicum belonged to the known order Chytridiales, while the two species of Zygorhizidium were placed in a novel clade that was previously reported as an undescribed clade composed of only the environmental sequences of uncultured chytrids.     

Some Observation on the Alga Fragilaria crotonensis Kitton and its Parasitism by Two Chytridiaceous Fungi

It has been shown by experimentation that two morphologicallydistinct clones of Fragilaria crotonensis Kitton, isolated fromthe plankton of Windermere at approximately the same time, wereaffected quite differently by the chytrid Rhizophydium fragilariaeCanter. In one case the diatom filaments became heavily parasitizedand could be used for the maintenance of the fungus. In theother case infection was negligible. Additional clones, representative of these two morphologicalforms, from other bodies of water in the Windermere drainagebasin were tested. The same pattern of infection or relativenon-infection again ensued in direct accordance with the particulartype of filament used. Some preliminary experiments undertaken with a second, as yetlittle known chytrid parasite of F. crotonensis are reported.In this instance the fungus appeared to find its natural hoston cells belonging to the morphological form which failed tosupport the continued increase of R. fragilariae. The parasitism of morphological variants of F. crotonensis bythese fungi in the wild from Britain and else where is discussed. Fragilaria crotonensis Kitton, Rhizophydium fragilariae Canter, chytrid, diatom, parasitism, culture     

Maranta rugosa sp. nov. (Marantaceae) from central Brazil

Maranta is a neotropical genus usually found in moist and shaded habitats in pluvial to semideciduous forests and Cerrado, with diversity center in central Brazil. A new species from Mato Grosso, M. rugosa J. M. A. Braga & S. Vieira, is described and illustrated. The new species is somewhat similar to M. parvifolia Petersen with which it is compared.     

The influence of phosphorus limitation of the diatomAsterionella Formosa on the zoospore production of its fungal parasiteRhizophydium Planktonicum

The influence of phosphorus limitedAsterionella on the zoospore production of its fungal parasiteRhizophydium planktonicum was measured, using laboratory cultures of host and parasite. At saturated phosphorus concentrations the host reached a specific growth rate of 0.95.d^–1. Growing on these host cells, the mean parasite zoospore production was 26 spores per sporangium, and the mean development time of a sporangium was 45 hours. Growing on phosphorus limited hosts, the zoospore production decreased to less then 9 spores per sporangium, and the development time decreased to 40 hours. On phosphorus limited hosts, zoospores were produced at a slower rate. The algal growth rate was reduced to a greater extent than the fungal growth rate. Therefore, it could be concluded that phosphorus limitation ofAsterionella will facilitate the development of an epidemic of its parasiteRhizophidium, at least at high diatom densities, when possible differences in infectability of the algae play a minor role.     

Rhizophydium brooksianum sp. nov., a multipored chytrid from soil

Rhizophydium136 was isolated from pollen bait placed in a water culture containing garden soil from Penobscot County, Maine. It is an important isolate because its entire mitochondrial genome has been sequenced and it is the representative member of the Chytridiales in a fungal phylogeny based on mitochondrial protein sequences. Also, this isolate is included in an 18S rDNA, chytrid phylogeny. On nutrient agar, many inflated rhizoidal axes extend from the base of the zoosporangium, zoosporangia mature in 3 d and zoospores discharge through numerous, lenticular, discharge pores. Smooth-walled resting spores form in crowded cultures. Zoospores are a variation of the Rhizophydium subtype. This chytrid differs from R. sphaerotheca sensu Barr and because it cannot be placed in a described species it herein is described as Rhizophydium brooksianum sp. nov. Many of the differences between Rhizophydium brooksianum and other multipored Rhizophydium isolates were observed only in pure culture. Attributing a spherical, multipored Rhizophydium to a species that was described without developmental information from pure culture is untenable. Epitypes or neotypes for inadequately characterized species need to be selected, and cultures made available.     

Some zoosporic fungi of New Zealand

Summary In further studies of the zoosporic fungi of New Zealand nine additional species were isolated on various substrata from soil. These include Rhizophydium pythii de Wildemann, R. condylosum Karling, Rhizophlyctis oceanis Karling, R. ingoldii Sparrow, R. boneysi Sparrow, Rhizophlyctis sp., Rhizidium reniformis sp. nov., Chytriomyces rotoruaensis sp. nov., Sparrowia parasitica Willoughby, and Aphanomycopsis punctatus Karling. Rhizidium reniformis is characterized by predominantly reniform, appendiculate zoosporangia and small zoospores which emerge slowly in a columnar mass. This usually floats away from the zoosporangium and explands, and after a while the zoospores swarm collectively in a vesicle. Chytriomyces rotoruaensis resembles R. reniformis by the structure and appearance of its thallus and behavior of the zoospores after discharge, but differs by the presence of a thin inconspicuous operculum and the development of smooth hyaline resting spores with coarsely granular content. Rhizophlyctis ingoldii, Sparrowia parasitica, and R. boneysi, known previously only from England and Hawaii, respectively, occurred abundantly in New Zealand.This study has been supported by a grant from the National Science Foundation, Washington, D.C.     

The influence of water and sediment properties on the occurrence of Potamocaris Dussart, 1979 (Harpacticoida) in the upper Paraná River (Brazil)

In the main channel of the Upper Paraná River, four sampling sites were established according to the profile of the bottom. Samples were carried out monthly from July 1993 to February 1995 with a modified Petersen grab. Four species were found at four sites: Potamocaris bifida, P. bidens, P. bidentata and P. tridentata. Canonical correspondence analysis indicated differences in the preferred microhabitats of the Potamocaris species, mainly in regard to sand particle size in the main river channel. Bedform stability was the most important factor affecting the abundance of this community.     

HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (CHYTRIDIOMYCOTA)1

Some chytrids are host‐specific parasiticfungithat may have a considerable impact on phytoplankton dynamics. The phylum Chytridiomycota contains one class, the Chytridiomycetes, and is composed of five different orders. Molecular studies now firmly place the Chytridiomycota within the fungal kingdom. Chytrids are characterized by having zoospores, a motile stage in their life cycle. Zoospores are attracted to the host cell by specific signals. No single physical–chemical factor has been found that fully explains the dynamics of chytrid epidemics in the field. Fungal periodicity was primarily related to host cell density. The absence of aggregated distributions of chytrids on their hosts suggested that their hosts did not vary in their susceptibility to infection. A parasite can only become epidemic when it grows faster than the host. Therefore, it has been suggested that epidemics in phytoplankton populations arise when growth conditions for the host are unfavorable. No support for such a generalization was found, however. Growth of the parasitic fungus Rhizophydium planktonicum Canter emend, parasitic on the diatom Asterionella formosa Hassal, was reduced under stringent nutrient limitation,because production and infectivity of zoospores were affected negatively. A moderate phosphorous or light limitation favored epidemic development, however. Chytrid infections have been shown to affect competition between their algal hosts and in this way altered phytoplankton succession. There is potential for coevolution between Asterionella and the chytrid Zygorhizidium planktonicum Canter based on clear reciprocal fitness costs, absence of overall infective parasite strains, and possibly a genetic basis for host susceptibility and parasite infectivity.     

Chemotaxis in the Marine Fungus Rhizophydium littoreum

Zoospores of the marine chytrid Rhizophydium littoreum are attracted to a variety of substances common to their environment. In general, carbohydrates and polysaccharides elicited strong concentration-dependent positive responses. There was no direct correlation between all substances used as foods and those stimulating positive responses. The chemotactic activities of this organism should, however, tend to bring it toward concentrated food sources.     

POLYOL PATTERNS IN BIOFILM‐FORMING AEROTERRESTRIAL GREEN ALGAE (TREBOUXIOPHYCEAE,CHLOROPHYTA)1

The distribution of polyols was examined for the first time in 34 green algal strains from four different clades belonging to the class Trebouxiophyceae, which dominate aeroterrestrial biofilms of many regions. Sorbitol was detected in representatives of the Prasiola clade, while ribitol was present in the Elliptochloris and Watanabea clades. Apatococcus lobatus (Chodat) J. B. Petersen contained erythritol in addition to ribitol. Polyols are considered as effective stress metabolites exerting multiple protective functions in metabolism and hence mainly occur in organisms colonizing extreme environments. In contrast, members of the Chlorella clade, which mainly occur in aquatic habitats, did not contain polyols. Thus, the constitutive presence of specific polyols facilitates a differentiation between species of the Prasiola clade from the Elliptochloris and Watanabea clades, respectively, and further allows differentiation of morphologically converging taxa.