| SS4.02 Ecology and Physiology of Marine Organisms: Insights from Genes, Genomes, and Proteomes |
| Ahlgren, N, A, University of Washington, Seattle, USA, nahlgren@ocean.washington.edu |
| Hook, H, E, University of Washington, Seattle, USA, handh02@u.washington.edu |
| Rocap, G, , University of Washington, Seattle, USA, rocap@ocean.washington.edu |
| |
| A NOVEL CLADE OF MARINE SYNECHOCOCCUS DEFICIENT IN NITRATE UTILIZATION |
 |
| The picocyanobacteria Synechococcus are found throughout the world’s oligotrophic and coastal waters. Although most strains of Synechococcus in culture were originally isolated using nitrate, a few strains which cannot grow on nitrate as a sole nitrogen source have been described recently. To further explore nitrogen utilization in Synechococcus, we isolated cyanobacteria from a well-mixed water column from the Sargasso Sea in March 2002 using either ammonium, nitrite, or nitrate as the sole nitrogen source. Partial sequencing of the 16S-23S rDNA internal transcribed spacer from 106 clonal isolates revealed at least 3 new phylogenetic clades of Synechococcus, including one which contains only strains isolated on ammonium. Growth experiments reveal that all strains tested from this group can grow on ammonium and nitrite but not nitrate. Guided by the genome of Synechococcus strain WH8102, we are exploring the genetic mechanisms behind this deficiency. These strains suggest that the inability to utilize nitrate may be more widespread among field populations of marine Synechococcus than previously thought, and this may have implications for our understanding of nitrogen cycling in oligotrophic systems. |
|
|