Chytrid infections of Daphnia pulicaria: development, ecology, pathology and phylogeny of Polycaryum laeve

1. We combined ecological surveys, life table studies, microscopy and molecular sequencing to determine the development, ecology, pathology and phylogeny of Polycaryum laeve, an endoparasite of cladocerans. We report the first records of P. laeve from North America, where we have used a polymerase chain reaction primer and microscopic examination to confirm infections in 14 lakes. Infections are highly pathogenic and caused increased mortality, reduced growth, and reproductive castration in Daphnia pulicaria during life table studies. 2. Biweekly data from Allequash Lake (Wisconsin, U.S.A.) throughout 2003 indicated that fecundity and infection prevalence were inversely correlated. Infection prevalence was highest in late winter and early spring (up to 80%) and lowest during late summer. Epidemics were generally followed by sharp declines in host population density (up to 99%). 3. Within the haemocoel of its host, P. laeve forms thick‐walled sporangia, which occur systemically in later stages of infection. Fungal thalli associate closely with muscle fibres and connective tissue, leading to degeneration as the infection becomes advanced. Following death of the host, flagellated zoospores are released through an exit papilla on the sporangium. Based on the infection‐induced castration of the host and increases in infection prevalence with Daphnia size, we postulate that transmission is horizontal, but may be indirect through an additional host or free‐living stage. 4. Molecular and morphological data clearly indicate that P. laeve belongs in the fungal phylum Chytriodiomycota, order Blastocladiales. Based on ribosomal RNA gene sequences and morphological features, we transfer the genus Polycaryum from the Haplosporidia to the Chytridiomycota, and designate a lectotype and epitype for P. laeve. Considering the high prevalence of P. laeve infection within Daphnia populations, the frequency with which we detected infections among lakes, and the keystone importance of large‐bodied Daphnia in aquatic food webs, we suggest that P. laeve may exert a regulatory influence on Daphnia populations in lake ecosystems.     

Infection experiments reveal broad host ranges of Eurychasma dicksonii (Oomycota) and Chytridium polysiphoniae (Chytridiomycota), two eukaryotic parasites in marine brown algae (Phaeophyceae)

Unialgal cultures of the brown alga Pylaiella littoralis (L.) Kjellman infected by either Eurychasma dicksonii (Wright) Magnus (Oomycota) or Chytridium polysiphoniae (Cohn) H. E. Petersen (Chytridiomycota) were used to elaborate the host ranges of these pathogens. Infection experiments with 48 host species covering 13 orders of the Phaeophyceae showed that 45 species were susceptible to attack by Eurychasma and 23 to Chytridium. The two pathogens showed host-specific differences in generation times: while in Pylaiella the shortest cycles were 16 days for Eurychasma and 6 days for Chytridium, one and five days more, respectively, were required in Acinetospora. Heavy parasite attack on the microscopic stages of host species with heteromorphic life histories, like kelps (Laminariales), is documented and discussed as a potential regulatory factor for the population dynamics of macroalgae.     

Multiple zoosporic parasites pose a significant threat to amphibian populations

There is substantial evidence for the dominant role of Batrachochytrium dendrobatidis in amphibian population dynamics. However, a wide range of other pathogens could also be important in precipitating amphibian population declines, particularly in the face of climate change or other stressors. Here we discuss some examples of zoosporic parasites in the Chytridiomycota, Mesomycetozoa, Perkinsozoa and Oomycota, all of which infect amphibians in freshwater habitats. The pathosystem model provides an excellent basis for understanding host–parasite interactions. Chemotactic zoopores and several families of proteases facilitate infection. Introduction of non-native host may accelerate the dispersal of these parasites. Unlike B. dendrobatidis some of the other zoosporic parasites grow well at or slightly above 25 °C, and their growth rates are likely to increase with global warming. The interactions of parasites with each other and the combined effect of simultaneous infection with multiple species in amphibian populations remain to be carefully studied.     

Pendulichytrium sphaericum gen. et sp. nov. (Chytridiales,Chytriomycetaceae), a new chytrid parasitic on the diatom,Aulacoseira granulata

During the last decade, our concept of chytrid systematics has dramatically changed based on molecular phylogeny and zoospore ultrastructure. In contrast with well-studied saprotrophic chytrids, only a few obligate parasitic chytrids have been investigated with modern methods. Here, we investigate the novel chytrid culture KS93 that is parasitic on the diatom Aulacoseira granulata. Thallus morphology of KS93 was characterized by a spherical, stalked zoosporangium with a single, apical inoperculate discharge pore and zoospore discharge as a mass in a vesicle. A cross-inoculation experiment revealed that the infection of KS93 was specific to A. granulata. Zoospores of KS93 possessed the characters of the Group I type zoospore of the Chytriomycetaceae in the Chytridiales, but does not appear to have a paracrystalline inclusion. Additionally, KS93 also possessed a globule-type KAS (kinetosome-associated structure), first reported here for members of Chytriomycetaceae. In our molecular phylogeny, KS93 was placed in the basal position of the Chytriomycetaceae and was distinguished from any known species in the family. Morphological features of KS93 were distinct from those of any other taxa in the Chytriomycetaceae and from any described chytrids. Based on these results, we describe this chytrid as Pendulichytrium sphaericum gen. et sp. nov. in the family Chytriomycetaceae.     

What has happened to the “aquatic phycomycetes” (sensu Sparrow)? Part II: Shared properties of zoosporic true fungi and fungus-like microorganisms

Many species of zoosporic heterotrophic parasites, saprotrophs and mutualists in the Phyla Perkinsozoa (dinoflagellates), Oomycota, Hyphochytriomycota, Labyrinthulomycota and Phyomyxea share morphological characteristics with zoosporic true fungi especially with some of the Chytridiomycota and with fungus-like organisms in the Phyla Mesomycetozoea, Chytridiomycota and Aphelidae. These characteristics include chemotactic motile zoospores, zoosporangia which produce zoospores, thick walled resistant cysts, rhizoid-like structures, hyphal-like structures and cell walls surrounding the cells in several phases of their life cycle. These assemblages also inhabit both marine and freshwater ecosystems in which aquatic fungi and fungus-like organisms are found, have similar life cycles, grow on similar substrates, use similar infection strategies and infect some of the same host plants and animals. Many of these species were once included in the aquatic phycomycetes, an ecological assemblage of microorganisms but not a valid taxonomic group. Some of the shared characteristics are discussed in this review.     

The use of ETOH for the dilution of honey

Since the beginning of honey production, certain honey types are preferred because they taste better, are better for cooking, or do not rapidly crystallize. Pollen found in honey is used to determine the honey's type. Techniques used to extract pollen from honey vary in the amount of honey examined, the amount of water used to dilute the honey, and the time and speed of centrifugation. These variations address the disparity in pollen recovery that is due to the specific gravity and sinking rates of the different pollen types. Ethyl alcohol (ETOH) was used as a dilution liquid for honey and compared to two water-dilution techniques, one with a short centrifugation time (1?minute) and the other using a long centrifugation time (10?minutes). The ETOH samples were centrifuged for 3?minutes. All samples were centrifuged at 4000 r.p.m. Significantly higher pollen concentration values were found in the ETOH-diluted samples. Pollen concentration values of the ETOH-diluted samples were 5.26 times greater than water-diluted, short centrifugation samples, and 3.26 times greater than water-diluted, long centrifugation samples. ETOH-diluted samples produced 16% more taxa than the water-diluted short centrifugation technique, and 10% more taxa than the water-diluted long centrifugation technique. The pollen spectra were not consistent across the three techniques. Additional research is needed to determine the efficiency of other ETOH concentrations in recovering pollen from honey. We recommend that the ETOH-dilution technique become the standard technique for the extraction of pollen from honey for pollen analyses because of the improved pollen recovery.     

Chytrid mycoparasitism of entomophthoralean azygospores

Mycoparasitism – when one fungus parasitizes another – has been reported to affect Beauveria bassiana and mycorrhizal fungi in the field. However, mycoparasitism of any fungi in the Order Entomophthorales has never been reported before now. The majority of entomophthoralean species persist as resting spores (either zygospores or azygospores) in the environment and dormant entomophthoralean resting spores (whether formed as zygospores or azygospores) are thought to be especially well adapted for survival over long periods due to their thick double walls. Entomophthoralean resting spores can accumulate in the soil as large reservoirs of inoculum which can facilitate the onset and development of epizootics. We report parasitism of azygospores of the gypsy moth pathogen Entomophaga maimaiga caged in soil from southern Ohio by the chytrid fungus Gaertneriomyces semiglobifer. G. semiglobifer had previously been isolated from soil samples from North America, Europe and Australia or horse manure from Virginia. After isolation and identification of G. semiglobifer, azygospores of E. maimaiga exposed to zoospores of G. semiglobifer exhibited high levels of mycoparasitism and G. semiglobifer was subsequently reisolated from mycoparasitized resting spores. We discuss the importance of this finding to the epizootiology of insect diseases caused by entomophthoralean fungi.     

THALASSOCHYTRIUM GRACILARIOPSIDIS (CHYTRIDIOMYCOTA), GEN. ET SP. NOV., ENDOSYMBIOTIC IN GRACILARIOPSIS SP. (RHODOPHYCEAE)

Thalassochytrium gracilariopsidis gen. et sp. nov. is an endosymbiotic, polycentric, zoosporic fungus that infected cultures of the red alga Gracilariopsis sp. Based on the posteriorly uniflagellate zoospore and the platelike cristae of the mitochondria, the fungus is placed in the Chytridiomycota. Ultrastructurally, the fungal zoospore is distinguished by the anterior position of the kinetosome, a unique microbody-lipid globule complex, an electron-opaque helix associated with the kinetosome and lipid globules, and a beaked nucleus. Zoospores are positively phototactic, and the unusual helix might constitute part of the photosensory apparatus. Zoospores lack certain taxonomically important structures, such as a rumposome, props, a nonflagellated kinetosome, and flagellar roots. The organism does not fit into any described genus, and the features of its zoospore differ from those of any described order. The fungal thallus is polycentric with multinucleate, septate hyphae. Haustoria form within the algal cells. The fungus does not appear to cause major harm to its host and seems to be host specific. However, during intense sporulation of the fungus, degradation of host chloroplasts was observed in medullary cells.     

Alicean taxonomy–small characters made large

MOORE, R. T., 1989. Alicean taxonomy–small characters made large. The examination of fungal cytology using electron microscopy is detailed, using examples from the major taxonomic groups. In the higher fungi, differences in the ultrastructure of ascomycete and basidiomycete septa, and within the latter group, those of the Basidiomycota and Ustomycota, are discussed.