| 1. |
- Bråte, Jon, et al.
(author)
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Freshwater Perkinsea and marine-freshwater colonizations revealed by pyrosequencing and phylogeny of environmental rDNA
- 2010
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In: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:9, s. 1144-1153
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Journal article (peer-reviewed)abstract
- Protist parasites are ecologically important, as they can have great impact on host population dynamics and functioning of entire ecosystems. Nevertheless, little is known about their prevalence in aquatic habitats. Here, we investigate the diversity and distributional patterns of the protist parasites Perkinsus and Parvilucifera (Perkinsea). Our approach included 454 pyrosequencing of the 18S rDNA gene obtained from a high-altitude lake (Lake Finsevatn, Norway) and phylogenetic analyses of all publicly available sequences related to Perkinsea. The applied PCR primers target a 450 bp region that encompass the variable V4 region of the 18S rDNA gene and have been optimized for the Titanium upgrade of the 454 technology. Nearly 5000 sequences longer than 150 bp were recovered from nearly all eukaryotic supergroups, and of those, 13 unique sequences were affiliated to Perkinsea. Thus, our new strategy for 454 amplicon sequencing was able to recover a large diversity of distantly related eukaryotes and previously unknown species of Perkinsea. In addition, we identified 40 Perkinsea sequences in GenBank generated by other recent diversity surveys. Importantly, phylogenetic analyses of these sequences identified 17 habitat-specific marine and freshwater clades (PERK 1-17). Hence, only a few successful transitions between these habitats have taken place over the entire history of Perkinsea, suggesting that the boundary between marine and fresh waters may constitute a barrier to cross-colonizations for intracellular parasites.
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| 2. |
- Logares, Ramiro, et al.
(author)
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Infrequent marine-freshwater transitions in the microbial world
- 2009
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In: Trends in Microbiology. - : Elsevier BV. - 0966-842X .- 1878-4380. ; 17:9, s. 414-422
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Research review (peer-reviewed)abstract
- Until recently, the evolutionary relationships between marine and freshwater microbes were unclear, but the use of molecular phylogenies is beginning to shed light on this subject. An increasing amount of studies are showing that marine and freshwater microbes (including viruses) are usually not closely related, often grouping into distinct marine and freshwater phylogenetic clusters, similar to what has been reported before for macroorganisms. These studies indicate that marine–freshwater transitions have been infrequent events during the diversification of microbes and that most of these transitions occurred a long time ago in evolutionary terms. Here we discuss the significance of recent studies addressing this question and consider possible avenues for future research.
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