Microbial grazers may aid in controlling infections caused by aquatic zoosporic fungi

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid Batrachochytrium dendrobatidis (Bd) a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores (∼3 µm), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate Tetrahymena pyriformis, which likely co-occurs with Bd, grew at near its maximum rate (r = 1.7 d-1). A functional response (ingestion vs. prey abundance) for T. pyriformis, measured using spore-surrogates (microspheres) revealed maximum ingestion (Imax) of 1.63 × 103 zoospores d-1, with a half saturation constant (k) of 5.75 × 103 zoospores ml-1. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control Bd and potentially prevent chytridiomycosis (defined as 104 sporangia host-1). However, simulated inferior micrograzers (0.7 x Imax and 1.5 x k) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modelling disease dynamics for Bd and other zoosporic fungi.

New insights into the evolutionary history of Fungi from a 407 Ma Blastocladiomycota fossil showing a complex hyphal thallus

Zoosporic fungi are key saprotrophs and parasites of plants, animals and other fungi, playing important roles in ecosystems. They comprise at least three phyla, of which two, Chytridiomycota and Blastocladiomycota, developed a range of thallus morphologies including branching hyphae. Here we describe Retesporangicus lyonii gen. et sp. nov., an exceptionally well preserved fossil, which is the earliest known to produce multiple sporangia on an expanded hyphal network. To better characterize the fungus we develop a new method to render surfaces from image stacks generated by confocal laser scanning microscopy. Here, the method helps to reveal thallus structure. Comparisons with cultures of living species and character state reconstructions analysed against recent molecular phylogenies of 24 modern zoosporic fungi indicate an affinity with Blastocladiomycota. We argue that in zoosporic fungi, kinds of filaments such as hyphae, rhizoids and rhizomycelium are developmentally similar structures adapted for varied functions including nutrient absorption and anchorage. The fossil is the earliest known type to develop hyphae which likely served as a saprotrophic adaptation to patchy resource availability. Evidence from the Rhynie chert provides our earliest insights into the biology of fungi and their roles in the environment. It demonstrates that zoosporic fungi were already diverse in 407 million-year-old terrestrial ecosystems. This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.

The genus Allomyces (Blastocladiomycota) in the State of Piauí, Brazil

ABSTRACT Brazilian ecosystems have been intensively exploited for agricultural expansion, however, the diversity of zoosporic organisms in such biomes remains little known. Therefore, further research is required to better understand their role within these ecosystems. Studies with zoosporic fungi were carried out and 22 Allomyces isolates were obtained from soil samples collected at six municipalities from Piauí State. After identification procedures, the taxa were grouped into four species: A. anomalus R. Emers., A. arbusculus E.J. Butler, A. moniliformis Coker & Braxton, and A. neomoniliformis Indoh. A. arbusculus had the highest rate of resistant sporangia viability (10%) and the largest geographical distribution in Piauí, occurring in seven out of ten sites studied. Countrywide, they occur within 14 municipalities from three states. Greater knowledge about the geographical distribution of Allomyces in Brazil is being pioneered in the State of Piauí. Novel information regarding the diversity and occurrence, as well as taxonomic characteristics of the isolates is presented herein.

Evaluation of Daphnid Grazing on Microscopic Zoosporic Fungi by Using Comparative Threshold Cycle Quantitative PCR

ABSTRACTLethal parasitism of large phytoplankton by chytrids (microscopic zoosporic fungi) may play an important role in organic matter and nutrient cycling in aquatic environments by shunting carbon away from hosts and into much smaller zoospores, which are more readily consumed by zooplankton. This pathway provides a mechanism to more efficiently retain carbon within food webs and reduce export losses. However, challenges in accurate identification and quantification of chytrids have prevented a robust assessment of the relative importance of parasitism for carbon and energy flows within aquatic systems. The use of molecular techniques has greatly advanced our ability to detect small, nondescript microorganisms in aquatic environments in recent years, including chytrids. We used quantitative PCR (qPCR) to quantify the consumption of zoospores byDaphniain laboratory experiments using a culture-based comparative threshold cycle (CT) method. We successfully quantified the reduction of zoospores in water samples duringDaphniagrazing and confirmed the presence of chytrid DNA inside the daphnid gut. We demonstrate that comparativeCTqPCR is a robust and effective method to quantify zoospores and evaluate zoospore grazing by zooplankton and will aid in better understanding how chytrids contribute to organic matter cycling and trophic energy transfer within food webs.IMPORTANCEThe study of aquatic fungi is often complicated by the fact that they possess complex life cycles that include a variety of morphological forms. Studies that rely on morphological characteristics to quantify the abundances of all stages of the fungal life cycle face the challenge of correctly identifying and enumerating the nondescript zoospores. These zoospores, however, provide an important trophic link between large colonial phytoplankton and zooplankton: that is, once the carbon is liberated from phytoplankton into the parasitic zoospores, the latter are consumed by zooplankton and carbon is retained in the aquatic food web rather than exported from the system. This study provides a tool to quantify zoospores and evaluate the consumption of zoospores by zooplankton in order to further our understanding of their role in food web dynamics.

Chitinophilic zoosporic fungi in various types of water bodies

Chitinophilic fungi in various types of water bodies (slough, pond, beach pool, two lakes and two rivers) were studied. Samples of water were collected every other month for hydrochemical analysis and once a month ( 1992 - 1994) in order to determine the fungus content. The wings of dragonfly and flies, carapaces of crayfish and potato beetle and the fructification of two mushrooms were used as bait. Thirty species of chitinophilic fungi were found in various types of water bodiss. <i>Cytriomyces annulatus, Entophlyctis crenata, Obelidium megarrhizum, Rhopalophlyctis sareoptoides, Achlya colorata, A. megasperma</i> and <i>Dictyuchus monosporus</i> represent new records as chitinophilic fungi. However, <i>Entophlyctis crenata, Obelidium megarrhizum</i> and <i>Podochytrium chitinophilum</i> reported for the first time from Poland.

Zoosporic fungi in springs in the vicinity of Białystok

Zoosporic fungi and environmental factors in 5 springs were analysed at monthly intervals for one year. A total of 83 zoosporic fungus species were noted. 13 species are new to the hydromycoflora of Poland.

Zoosporic fungi growing on bird excrements in the water of the river Biała

The coprophilic fungi i n the water of river Biała were studied. Samples of water were collected every o the r month for hydrochemical analysis and once (1994/95) in order to determine the fungus content. The excrements of 9 species of bird were used as bait. Thirty-one species of coprophilic fungi were found in the water of the river Biała. <i>Apodachlya punctata, Pythium catenulatum, Saprolcgnia asterophoru</i> and <i>S. megasperma</i> new records for Poland.