New insights on the ecology of free-living heterotrophic nanoflagellates based on the use of molecular biological approaches
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https://hdl.handle.net/1912/5696DOI
10.1575/1912/5696Abstract
Nanoplanktonic protists comprise a diverse assemblage of flagellate species
responsible for various trophic processes in marine and freshwater ecosystems.
Current methods for identifying small protists do not readily permit identification and
enumeration of nanoplanktonic flagellates in cultures or field samples. The aim of this
study was to apply molecular biological techniques for identification and enumeration of
nanoflagellate taxa in water samples.
Restriction fragment length polymorphism (RFLP) analysis of small subunit
ribosomal DNA (SSU rONA) amplified by the polymerase chain reaction (PCR)
differentiated pure cultures of heterotrophic nanoflagellates according to established
taxonomic classification at the generic and species level. In addition, RFLP analysis of
amplified SSU rONA permitted discrimination of polymorphic forms among species of
flagellates from the genus Paraphysomonas.
A fluorescent in situ hybridization method that uses rRNA-targeted
oligonucleotide probes for counting protists from cultures and environmental water
samples was developed. Preserved cells were intensely labeled with multiple eukaryote-specific oligonucleotide probes end-labeled with biotin and detected by
fluorescein (FITC)-avidin. This probe hybridization method gave estimates of
nanoplankton abundances that were often more representative of natural abundances than
estimates obtained by commonly employed fluorochrome stains.
The geographical distribution and seasonal abundance of the cosmopolitan
heterotrophic flagellate, Paraphysomonas imperforata was examined in coastal waters
using species-specific oligonucleotide probes. P. imperforata was found to occur at
extremely low abundances in coastal environments, constituting ≤1% of the TNAN.
However, P. imperforata often dominated the nanoplankton (up to 98% of TNAN) when
water samples were enriched with bacteria. P. imperforata appears to be an
opportunistic species capable of growing rapidly to high abundances when prey are
abundant. Water temperature, small differences in the absolute abundance of P.
imperforata, and nanoplankton grazers appeared to play a role in determining P.
imperforata dominance. Results from this study also suggest that enrichment cultivation
or perhaps incubations in general can select for nanoflagellates such as P. imperforata
that may not be representative of abundant oceanic species.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution March 1997
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Suggested Citation
Thesis: Lim, Ee Lin, "New insights on the ecology of free-living heterotrophic nanoflagellates based on the use of molecular biological approaches", 1997-03, DOI:10.1575/1912/5696, https://hdl.handle.net/1912/5696Related items
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