Laboratory of Fish Protistology

Mission

Our main interests are eukaryotic microorganisms infecting fish, amphibians and reptiles, including all aspects of their structure, biology, life cycles, host-parasite interactions, ecology and especially their phylogeny and evolution. Our two main focuses are 1. The Myxozoa, and 2. Amoeboid organisms, but we also study other interesting microparasites like e.g. apicomplexans, microsporidians, ciliates or dinoflagellates. As part of our work we carry out research into a range of parasite problems which create economic and health consequences for the aquaculture industry, in collaboration with various institutions worldwide.

Head: Astrid Holzer

Selected publications

International collaboration

Graduated students

Current research projects

MYXOZOA

Myxozoans are diverse and widely distributed metazoan parasites predominantly of fish and are closely related to Cnidaria. They have a complex life cycle involving a vertebrate (fish) and an invertebrate (bryozoan, polychaete or oligochaete) host and some species cause important losses in the aquaculture sector. We conduct a wide range of studies on myxozoans:

Phylogeny and evolution

Myxosporean phylogenetric tree with spore morphology

For historical reasons, current myxozoan taxonomy is based predominantly on the morphology and structure of the spores produced in the vertebrate (fish) host. We have shown that the phylogenetic relationships among the myxozoans based on different gene regions disagree with the traditional taxonomic classification: a number of myxosporeans with very similar spore morphology and belonging to the same genus were found to be phylogenetically distantly related, rendering most genera non-monophyletic (Holzer et al. 2004, Fiala 2006, Holzer et al. 2007, Bartošováet al. 2009, Fiala & Bartošová 2010). One of our principal aims is to solve the controversy between morphology and phylogeny in the Myxozoa by designing a taxonomic system which is able to correctly classify newly described species. We are thus trying to obtain DNA sequences for a number of representatives of each genus, conduct phylogenetic analyses and investigate differences with regard to their biology, in order to be able to understand why they cluster in different branches of the tree. This will allow us to identify the characters which shape myxosporean evolution and will lead to a better understanding of the broad diversity of modern species.

Investigations into myxozoan life cycles and development

Ceratomyxa puntazzi proliferative parasite stages

We are currently studying the transmission, seasonality and development of different myxozoans in cyprinids in the Czech Republic as well as in Mediterranean cultured sea bass Dicentrarchus labrax, sea bream Sparus aurata and sharpsnout sea bream Diplodus puntazzi, the latter in collaboration with the University of Bologna (Italy) and the University of Valencia (Spain). As part of these studies in the bile myxozoan Ceratomyxa puntazzi, we recently described the cellular components and mechanisms involved in myxozoan motility, and showed how the same elements are implicated into the processes of budding and cytokinesis in the Myxozoa (Alama-Bermejo et al., 2012 in press). We demonstrate that F-actin-rich cytoskeletal elements polarize at one end of the parasites and in the filopodia which are rapidly de novo created and re-absorbed, thus facilitating unidirectional parasite motility in the bile. We furthermore discovered that the mechanism of budding is an active polarization process of cytokinesis, which is independent from a contractile ring and thus differs from the mechanism, generally observed in eurkaryotic cells.

Myxozoans in amphibians

Sphaerospora ranae

Using both structural (morphology, incl. ultrastructure) and molecular phylogenetic tools, we characterize and compare myxozoan parasites from amphibians originating from all biogeographic realms. Data collected to date have allowed for unique insights into their diversity, ecology, epidemiology, and biogeography. One particular study (Hartigan et al. 2011) focused on myxozoan diseases affecting naïve host populations which is a key threatening process contributing to the precipitous global decline of biodiversity. This research was conducted in collaboration with the University of Sydney (Australia) and it investigated (and implied) the suspected spread of Myxidiumspp. among endemic Australian frog populations by introduction of the Cane toad from Neotropics. Plotting minimum within-group distance against maximum intra-group molecular distances confirmed independent evolutionary trajectory of Australian and Neotropical myxosporeans. These data suggest that the Cane toad may have played an important spill-back role in parasite emergence (which probably had limited distribution/host spectrum before) and may have facilitated their dissemination.

AMOEBOID PROTISTS

The research of amoebae in our lab is focused mainly on so-called amphizoic amoebae parasitizing fish. They are mostly free-living organisms living in aquatic environments which are, under certain circumstances, able to cause more or less severe infections of fish.

Pathological species

Nodular gill disease in rainbow trout (Oncorhynchus mykiss)

Amoebae are often found on the gills of their fish hosts, but some may invade their internal organs. An example of pathogenic amoebae is the genus Neoparamoeba, that causes a pathological condition in marine fish called "amoebic gill disease" (see e.g., Dyková et al., 2007), or several genera (e.g., Cochliopodium, Naegleria and others) that cause similar infections of fresh-water fish ("nodular gill disease" – Dyková et al. 2010). We also study amoebae associated with deaths of invertebrates (e.g. sea urchins – Dykova et al. 2011) and amoebae isolated from various fresh-water and marine environments, some of which are potential pathogens for fish.

Phylogeography, ecology and endosymbionts

Neoparamoeba

We use amoebae as model organisms in order to address general questions regarding the phylogeography or ecology of these special eukaryotes. Specifically, we study how widespread are amoebae species throughout the globe including some extremely cold localities (Svalbard – Centre for Polar Ecology of the University of South Bohemia, located near Billefjorden). Some of the amoebae isolated in our lab live in interesting symbioses with other organisms - for example the mentioned Neoparamoeba is a host of intracellular, unicellular eukaryotes  - kinetoplastids (Dyková et al. 2008). Other amoebae can be inhabited by bacteria etc. These cases can serve as models for the studies of coevolution, reduction of endosymbionts, gene transfer and so on.

Diversity of Amoebae

Grellamoeba robusta

We use morphological, ultrastructural and molecular methods in combination with modern phylogenetic methods to identify the genus/species of a given isolate. Isolates, which were thoroughly studied, are cryopreserved for future use - our collection of cryopreserved amoebae is unique as it contains hundreds of strains. The documentation of this collection is the content of a book that is to be published in 2012 (Dyková &Kostka: Illustrated Guide to Culture Collection of Free-living Amoebae). It should be mentioned that the term "amoeba" does not correspond to any monophyletic organismal group: from the taxonomical point of view, "amoebae" are an assamblage of several unrelated groups of organisms, although they are morphologically more or less similar. This is in fact what makes the work with amoebae even more interesting for a phylogenetist, as among the strains isolated in our lab can be found representatives of various important eukaryotic groups (Amoebozoa, Heterolobosea, Opisthokonta, Rhizaria). Phylogenetic studies of the isolates then can alter the hypotheses on phylogeny of large eukaryotic groups or, thanks to the key position of some groups of amoebae, of eukaryotes as a whole. Discoveries of new taxa are guaranteed (Dyková et al. 2010)!

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Sections > Organismal and Evolutionary Parasitology > Laboratory of Fish Protistology