SS2.03 Phytoplankton Ecology Using Molecular Approach
Date: Thursday, June 13, 2002
Time: 2:15:00 PM
Location: Colwood
 
ZehrJP, University of California, Santa Cruz, CA, USA, zehrj@cats.ucsc.edu
Steward, G, F, U. of Hawaii, Honolulu, HI, USA, gsteward@soest.hawaii.edu
Omoregie, E, O, University of California, Santa Cruz, CA, USA, enomao@cats.ucsc.edu
Montoya, J, P, Georgia Inst. of Technology, Atlanta, GA, USA, joseph.montoya@biology.gatech.edu
 
NITROGENASE GENE EXPRESSION IN AQUATIC NITROGEN-FIXING CYANOBACTERIA
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Phytoplankton biochemical activities can be measured directly in bulk assays without knowledge of the taxa or phylotypes involved, but a mechanistic understanding of nitrogen cycling in the food web requires information on individual species. We have used cloning and sequencing of gene transcripts to infer the contribution of different organisms to nitrogen fixation in an oligotrophic subtropical gyre. Unicellular cyanobacteria were found to express nitrogenase in natural samples and in nutrient enrichment experiments. In size fractionation assays, the activity of multiple diazotrophic cyanobacteria could be ascertained from the molecular sequence of the nifH sequence amplified by RT-PCR. These included Trichodesmium, sequences believed to be derived from the diatom symbiont Richelia, and the unicellular marine Synechocystis previously discovered at station ALOHA. Along with the expression by these multiple types of cyanobacterial diazaotrophs, nifH gene expression by heterotrophic bacteria was also detected. Studying simultaneous expression by multiple phylotypes can be facilitated by new technologies in transcriptomics, including expression microarrays and quantitative PCR. We will present our application of these newer techniques to the study of nitrogen fixation in the environment.