NANOPLANKTONIC PROTISTS IN MARINE ENVIRONMENTS: ANALYSIS OF NATURAL ASSEMBLAGES USING MOLECULAR APPROACHES
Phototrophic and heterotrophic nanoplanktonic protists (microalgae and protozoa 2-20 um in size) are integral components of marine plankton communities. These single-celled, eukaryotic microorganisms play major roles as primary producers and micro-consumers in pelagic ecosystems. Current methodologies for enumerating phototrophic nanoplankton (PNAN) and heterotrophic nanoplankton (HNAN) cannot provide more than cursory information on the species diversity, specific trophic roles, taxonomic identity or biogeography of these assemblages. There is a clear need to apply new methodologies to allow a more thorough characterization of PNAN and HNAN assemblages. Molecular techniques and a newly-developed quantitative in situ hybridization method will be applied to natural assemblages of protists in order to assess nanoprotistan diversity, and to identify and quantify the predominantly occurring nanoplanktonic protistan species. The main focus of this work will be to obtain sequence information (small subunit rRNA) from natural assemblages of protists, to relate these sequences to protistan species in natural water samples (morphospecies), and to assess the abundances and distributions of target species for which we are continually designing and testing oligonucleotide probes. This work will be conducted within the context of experiments to examine shifts in species composition of the protistan assemblage in response to containment, long-term incubation (24-96 hr), and enrichment. Work on the population dynamics of individual taxa will begin using oligonucleotide probes developed for species of the heterotrophic chrysomonad genus Paraphysomonas and the bicosoecid species Cafeteria roenbergensis, and a quantitative in situ hybridization method. The project will provide important information on the species diversity of natural protistan assemblages using modern molecular biological approaches. Additionally, this work will provide a working model system in which to further refine and optimize these molecular techniques for routine field applications in microbial ecology.
