Experiments linking nitrogenase gene expression to nitrogen fixation in the North Pacific subtropical gyre

Jonathan P. Zehr, Joseph P. Montoya, Bethany D. Jenkins, Ian Hewson, Elizabeth Mondragon, Cindy M. Short, Matthew J. Church, Andrew Hansen, David M. Karl

Research output: Contribution to journalArticlepeer-review

Abstract

We examined diazotroph activity in controlled experiments containing natural populations of nitrogen (N2)-fixing microbes collected offshore from Kane'ohe Bay, Hawai'i, and from Station ALOHA (A Long-term Oligotrophic Habitat Assessment) in the North Pacific subtropical gyre. Quantitative polymerase chain reaction and reverse transcription-polymerase chain reaction approaches showed that the abundances of the major phylotypes did not change substantially during experimental incubations. Diel phasing of nifH gene expression in the experiments was similar to that documented for natural populations. Cell-specific N2 fixation rates, calculated as 15N2 incorporation rate divided by specific phylotype abundance (gene copy number), varied between the experiments, but generally agreed with the abundance and levels of nifH expression of each group of diazotrophs. Phosphorus additions had little effect on the abundance, gene expression, or N2 fixation activity of diazotrophs across the course of the 36-h experiments, indicating that other factors may limit the growth, gene expression, and activity of diazotrophs in the North Pacific subtropical gyre.

Original languageEnglish
Pages (from-to)169-183
Number of pages15
JournalLimnology and Oceanography
Volume52
Issue number1
DOIs
StatePublished - Jan 2007

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