In addition to nitrogen and phosphorus, iron is an essential nutrient for oceanic primary productivity. Unlike nitrogen and phosphorus however, negligible amounts of iron are supplied to surface waters through recycling or mixing but instead from the limited and sporadic input of aeolian particulate. The low concentration of iron that becomes biologically available from the dust places a serious constraint on the heavily iron-dependent processes of photosynthesis and nitrate reduction which affect primary productivity. As much as 47% of the total oceanic primary productivity can be attributed to cyanobacteria making them critical organisms in the biogeochemical cycles. This thesis addresses the effect of iron on primary productivity using a combined approach of physiological and molecular biology. The physiological response of three marine strains of Synechococcus to growth on different concentrations of FeEDTA was investigated. Cells grown with higher concentrations of iron had greater cell density, more Chl- and phycobiliproteins and higher carbon fixation rates than cells grown at limiting iron concentrations (l0-8 M Fe). Iron enrichment of iron limited cultures stimulated carbon fixation, growth rate, and pigment and protein synthesis. Iron limited cells spiked with SJ.l.M Nlf4Cl prior to short term incubations had higher dark carbon fixation than cells gro·wn at higher iron and also spiked to 5J.1M Nlf4Cl. The addition of ammonium relieves a restricted nitrogen assimilatory pathway in the low iron cells that is evidenced by increased dark carbon fixation. We propose that this measurement of enhanced dark carbon fixation could be a useful assay in supporting the contention that populations of Synechococcus in nitrate rich waters are iron limited. Molecular genetic techniques were used to look for the presence of an iron uptake gene in cyanobacteria. Preliminary results indicate that there is a gene that is homologous to the ferric uptake regulation (fur) gene in E. coli. This hybridization occurred in siderophore-producing cyanobacteria, but not in marine cyanobacteria that do not produce siderophores. The fact that marine Synechococcus do not produce siderophores and did not hybridize to the fur gene suggest that fundamentally different mechanisms for iron uptake operate in high biomass freshwater cyanobacteria and cyanobacteria from dilute oligotrophic waters.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5600 |
| Date | 02 August 1991 |
| Creators | Unsworth, Nancy Walters |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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