Idea Transcript
BO25F-11
Seasonal Variations and Diversity of Eukaryotic Microbial Assemblages across a River-to-Ocean Gradient using Molecular and Traditional Tools Peter Kahn1, L. Herfort1, T. Peterson1, L. McCue2, P. Zuber1 Center for Coastal Margin Observation and Prediction, Oregon Health & Science University, Beaverton, OR1; Pacific Northwest National Laboratory, Richland, WA2
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TEMPLATE DESIGN © 2008
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Cell counts: genus level
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Cell counts Class level
Example: July 2008 River
Clone library: genus level
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Stephanodiscus 14%
uncultured alveolate PAA9AU2004 27%
Stephanodiscus 10%
Skeletonema 18%
Heterotrophs
Fragilaria 10%
Synedra 10%
Freshwater Diatoms
Nitzschia 10%
• At genus level, cell counts have greater evenness, leading to greater diversity. Clone libraries have a greater tendency to be dominated by a single clone • Higher diversity shown by clone libraries at class level suggests that molecular tools are better able to detect nano- and picoeukaryotes
Autotrophs
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Autotrophs
Freshwater Diatoms
Clone Libraries
Cell Counts
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• Samples were collected during 5 cruises spanning 2007 and 2008 at 3 regions: river, estuary, and plume • Clone libraries generated through amplification of 18S rDNA gene via general eukaryotic primers Euk A (1-20) and Euk B (1780-1800) • 25 mL of formalin-fixed water (4% final concentration) was settled for microscopic cell counts using the Utermohl settling method (Utermohl, 1958) • Clone libraries and cell counts grouped according to class and genus to compare similarities and differences between the two methods 2008
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Conclusions Columbia River
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River
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July 2008
Cathlamet Bay
Class level
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Grays Bay
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Genus level
Baker Bay
Youngs Bay
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Clone libraries
Columbia River coastal margin
Plume
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Clone libraries show lower diversity at the genus level but higher diversity at the class level
April 2007/ 2008
The objective of this study was to compare assessments of eukaryotic microbial diversity, abundance, and community structure in the Columbia River and its coastal margin via 18S rDNA clone libraries and microscopic cell counts PACIFIC OCEAN
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Genus level
Freshwater Diatoms
Katablepharis
Similarity in percent representation of taxa in each method was assessed using the Bray Curtis index. Results showed that similarity between the two methods is almost twice as high at the class level than the genus level
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Heterotrophs
Shannon index (H')
Autotrophs
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Comparisons between methods
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Estuary
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Research goal
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heterotrophic protists, play important roles in energy transfer and nutrient transformations in the complex estuarine food web • To better understand how human perturbations are changing the estuarine food web, it is necessary to gain a more complete understanding of the seasonal and interannual dynamics of eukaryotic microbial communities • Morphologically based methods, such as light microscopy, have been used in the Columbia River estuary to characterize larger phytoplankton and heterotrophic protist communities, depicting a system dominated by freshwater diatoms (Williams 1964, 1972; Haertel et al. 1969; Frey et al. 1964) • Light microscopy is often unable to distinguish between nano and picoeukaryotes (0.2-20 µm) and may lead to an underestimation of diversity • Recent studies using molecular methods have revealed high levels of diversity in microeukaryotes in other aquatic environments (Díez et al. 2001; Šlapeta et al. 2005) • Molecular tools, such as rDNA cloning and sequence analysis, also have inherent biases that may cause misleading assessments of diversity • As eukaryotic metagenomic research moves forward, it is important to ground-truth this molecular data with traditional microscopic methods
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Seasonal variation of eukaryotic microbes in the Columbia River coastal margin assessed by 18S rDNA clone libraries and microscopic cell counts
Introduction • Eukaryotic microorganisms, such as phytoplankton and
Heterotrophs
• Diatoms are dominant throughout coastal margin during April and July, with the exception of Katablepharis clones dominating clone libraries in the estuary during April • A diatom-flagellate/ ciliate transition is evident during August 2007 and September 2008, with Myrionecta rubra blooms in the estuary and autotrophic and mixotrophic dinoflagellates in the plume • Clone libraries reveal the dominance (56%) of Katablepharis sp. at 15 PSU in April 2007 and April 2008, a 5 µm heterotrophic protist that was previously unrecorded in the Columbia River coastal margin. Given its high abundance and recurring patterns, it could be an important component of the aquatic food web, particularly in spring • An internal transcribed spacer (ITS) genetic marker has been developed for Katablepharis that will be used to track this protist’s development and distribution throughout the estuary over the year