Hidden diversity among aquatic heterotrophic flagellates: ecological potentials of zoosporic fungi

Abstract

International audienceSince the emergence of the ‘microbial loop' concept, heterotrophic flagellates have received particular attention as grazers in aquatic ecosystems. These microbes have historically been regarded incorrectly as a homogeneous group of bacterivorous protists in aquatic systems. More recently, environmental rDNA surveys of small heterotrophic flagellates in the pelagic zone of freshwater ecosystems have provided new insights. (i) The dominant phyla found by molecular studies differed significantly from those known from morphological studies with the light microscope, (ii) the retrieved phylotypes generally belong to well-established eukaryotic clades, but there is a very large diversity within these clades and (iii) a substantial part of the retrieved sequences cannot be assigned to bacterivorous but can be assigned instead to parasitic and saprophytic organisms, such as zoosporic true fungi (chytrids), fungus-like organisms (stramenopiles), or virulent alveolate parasites (Perkinsozoa and Amoebophrya sp.). All these microorganisms are able to produce small zoospores to assure dispersal in water during their life-cycles. Based on the existing literature on true fungi and fungus-like organisms, and on the more recently published eukaryotic rDNA environmental studies and morphological observations, we conclude that previously overlooked microbial diversity and related ecological potentials require intensive investigation (i) for an improved understanding of the roles of heterotrophic flagellates in pelagic ecosystems and (ii) to properly integrate the concept of ‘the microbial loop' into modern pelagic microbial ecology

Microeukaryote community composition assessed by pyrosequencing is associated with light availability and phytoplankton primary production along a lowland river

“…Microscopic eukaryotes are highly abundant in freshwater ecosystems, yet little is known about their diversity, food‐web linkages or their interaction with the surrounding environment (Sime‐Ngando, Lefevre & Gleason, ). Phytoplankton often perform the majority of primary production in large river systems, while micro‐ and juvenile metazoans, protists, ciliates and fungi function as consumers, decomposers and parasites (Schmid‐Araya & Schmid, ).…”

Exploring and quantifying fungal diversity in freshwater lake ecosystems using rDNA cloning/sequencing and SSU tag pyrosequencing

“…One chytrid species ( Batrachochytrium dendrobatidis ) was also described as the causative agent of die‐offs and population declines of amphibian species (Berger et al ., 1998). Previous studies have unveiled a large reservoir of unsuspected fungal diversity in pelagic zone of lakes (Van Donk and Ringelberg, 1983; Holfeld, 1998; Hyde and Goh, 1998a; Richards et al ., 2005), primarily of chytrids (Lefèvre et al ., 2007; 2008; Sime‐Ngando et al ., 2011) known as aquatic life forms, as their propagules (i.e. uniflagellated zoospores) have specialized aquatic dispersal abilities.…”

Intracellular eukaryotic pathogens in brown macroalgae in the Eastern Mediterranean, including LSU rRNA data for the oomycete Eurychasma dicksonii

“…The ecological role of zoosporic fungi and funguslike organisms is increasingly recognized in aquatic ecosystems, and those organisms represent an important and non-negligible part of the microbial loop , Sime-Ngando et al 2011. Furthermore, previously unknown taxa are described at high rates in freshwater and marine systems, including parasites of algae.…”