Host-parasite interactions : the Parvilucifera sinerae model in marine microalgae
Parasitism is a widespread interaction that has evolved practically in all branches of the tree of life. It has historically been neglected in studies of marine microbial systems, limiting our understanding of marine food webs and biogeochemical cycles. Molecular tools have recently revealed many ne...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2017 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/456807 |
| Acceso en línea: | http://hdl.handle.net/10803/456807 https://dx.doi.org/10.5821/dissertation-2117-111224 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria civil 58 |
| Sumario: | Parasitism is a widespread interaction that has evolved practically in all branches of the tree of life. It has historically been neglected in studies of marine microbial systems, limiting our understanding of marine food webs and biogeochemical cycles. Molecular tools have recently revealed many new host-parasite associations, placing parasites as key components of coastal marine planktonic and benthic communities. Phytoplankton sustains most of the marine primary production, sometimes causing massive proliferations or blooms, which may have negative consequences for humans and the ecosystem. Dinoflagellate blooms often occur in coastal areas, sometimes in co-occurrence with zoosporic parasite species. Occasionally, parasitic infections may be the main cause of dinoflagellate mortality, which can modulate bloom termination and consequently, their use has been suggested to biologically control natural blooms. Up to date, three groups of eukaryotic parasites of dinoflagellates have been described: Amoebophrya (Syndiniales), Parvilucifera (Perkinsozoa) and Dinomyces (Chytridiomycota). Such parasites can control the abundance of their hosts populations, and hence they can also affect phytoplankton dynamics, community structure and diversity. However, very little is still known about the ecology and diversity of these parasites, especially Parvilucifera and Dinomyces. Parvilucifera genus is one of the recently described groups of Perkinsozoa. To date, the genus comprises only 5 species, some of them described very recently. Most of the knowledge about this genus is related to the 18S rDNA sequences that allow its phylogenetic classification, and also with the morphological characters valuable for taxonomy studies. For this reason, this PhD thesis aims to better understand the microbial host-parasite interactions of marine planktonic communities by studying P. sinerae-dinoflagellates as a model system. Here we studied these host-parasite interactions at different scales, from cell-cell, to population and at community level, combining laboratory experiments and field studies. The use of several microscope techniques and molecular tools (TSA-FISH) have allowed the characterization of the life-cycle of P. sinerae and the kinetics of the infection stages. P. sinerae has a direct life cycle that causes the host death, with a short generation time and a high asexual reproduction rate, producing a huge offspring from a single infection (Chapter 1). Moreover, we unequivocally identified dymethilsulfide as the chemical cue that triggers zoospore activation and release from the dormant sporangium (Chapter 2). Our capacity to culture both partners of the association in the lab, P. sinerae and dinoflagellates, allowed for a series of cross-infection experiments, which resulted in the designation of P. sinerae as a generalist parasitoid, being able to infect up to 15 genera of dinoflagellates (Chapter 3). Furthermore, we determined that P. sinerae exhibits preferences for certain host species, which enhance parasitoid reproduction rate and transmission (Chapter 4). The study of in situ Parvilucifera detection and estimates of the flux of infected host cells using sediment traps has allowed us to unveil the occurrence, dynamics, and impact of Parvilucifera infection during Alexandrium minutum natural blooms (Chapter 5). We showed that outbreaks of the dinoflagellate A. minutum were always accompanied by Parvilucifera infections, presenting a host-parasitoid temporal dynamic similar to predator-prey interactions, and contributing to bloom decrease with a similar magnitude than other biological loss factors. The analysis of this relationship at different scales has provided the necessary information to conclude that the ecology of Parvilucifera is well adapted to that of its blooming hosts, whose seasonal proliferations enhance Parvilucifera transmission, sustaining the parasitic populations in marine coastal environments. |
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