Final Technical Report for 'Investigations of the Role of Protozoa in Transformations of Marine Biopolymers using Phaeocytis Polymer Gels as a Model'
OAK B188 Biopolymers and biopolymer gels are major components of the organic carbon and nitrogen pools in the ocean. The overall goal of this project was to better understand the chemical and physical transformations of polymers and polymer gels in coastal waters that are mediated by protists and bacteria. Bacteria are thought to be the major consumers of marine biopolymers, but direct consumption by protists, and the interactions of bacteria and protists, may also be important but largely unexplored pathways of biopolymer cycling. Phaeocystis is a colonial prymnesiophyte alga that produces large amounts of polymer gels that have similar properties to those found in the dissolved organic carbon (DOC) pool namely, they are tangled networks of polymers held together by calcium bridges. We used the polymers and polymer gels produced by two species of Phaeocystis (from the North Atlantic and Antarctica) as models to examine the consumption, degradation and alteration of algal polymer gels by protists and bacteria. We developed several novel methods and approaches to examine polymer gel transformations. One tool was an immunoassay (ELISA) using a polyclonal antibody specific to Phaeocystis polymers that allowed us to track the polymer gels in situ and in laboratory experiments. We successfully tested the ability of the immunoassay to detect and quantify Phaeocystis polymer carbon in water from the Ross Sea, Gulf of Alaska and North Water (Greenland). This exciting new approach demonstrates the usefulness of antibodies for detecting and quantifying a specific component of the DOM pool in natural samples and provides a method for following the sources and sinks of that component. We also developed a fluorescent immunoassay procedure with the antibody to visualize and quantify ingested polymers in single protist cells. In experiments with polymer gels as the sole organic source (no prey), prey plus polymer gels, and prey without polymer gels, we determined that some protists are able to use the polymer for nutrition and growth. This is the first demonstration of the ingestion and utilization of a natural marine biopolymer by protists. We also isolated three bacterial strains from our Phaeocystis cultures. All three bacterial strains were capable of growing solely on the polymer gels produced by Phaeocystis without added inorganic nitrogen sources. We used the bacterial and protist strains to investigate degradation and alterations (size, chemical composition) of Phaeocystis polymer gels by bacteria alone and in the presence of protists. In a typical experiment, bacterial abundance in the presence of protists was reduced to one third of that in the control due to grazing, but the degradation rate was about the same. This indicates either that grazing by the protist somehow enhanced the per cell rate of bacterial degradation and/or the protist was ingesting polymer directly. Residual polymer remained after weeks, but the mean the mean diameter of the polymers were shortened considerably to ca. 200 nm. These results, along with other lines of evidence, suggest that it may be the length of polymer that limits degradation, which has important implications for the large pool of refractory DOM in the oceans. Chemical analyses indicated that the polymers are carbohydrate-rich and that the nitrogen is not proteinaceous, but most likely in the form of low molecular weight compounds such as amino sugars or sialic acid, and that they had a surprisingly low C:N ratios (<9). Extracellular polymers may therefore provide a nutritional substrate for bacteria and protists without the need for other sources of nitrogen in nature.
- Research Organization:
- University of Washington (US)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- FG03-98ER62532
- OSTI ID:
- 809405
- Resource Relation:
- Other Information: PBD: 1 Apr 2003
- Country of Publication:
- United States
- Language:
- English
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Final report
Related Subjects
AMINES
CHEMICAL COMPOSITION
COASTAL WATERS
ENZYME IMMUNOASSAY
GULF OF ALASKA
MOLECULAR WEIGHT
PROTOZOA
SACCHARIDES
SIALIC ACID
TRANSFORMATIONS
MARINE BIOPOLYMER GELS
PHAEOCYSTIS POLYMER GELS
PROTOZOAN DEGRADATION OF POLYMER GELS
BACTERIAL DEGRADATION OF POLYMER GELS
IMMUNOASSAYS
PROTOZOAN AND BACTERIAL INTERACTIONS