4.0 Article

Coupled Effects of Light and Nitrogen Source on the Urea Cycle and Nitrogen Metabolism over a Diel Cycle in the Marine Diatom Thalassiosira pseudonana

期刊

PROTIST
卷 163, 期 2, 页码 232-251

出版社

ELSEVIER GMBH, URBAN & FISCHER VERLAG
DOI: 10.1016/j.protis.2011.07.008

关键词

Carbamoyl phosphate synthetase; glutamine synthetase; nitrogen metabolism; photorespiration; urea cycle; urease

资金

  1. Gordon and Betty Moore Foundation
  2. Pacific Northwest Center for Human Health and Ocean Studies (NIH/National Institute of Environmental Health) [P50 ES012762]
  3. Pacific Northwest Center for Human Health and Ocean Studies (National Science Foundation) [OCE-0910624]
  4. Division Of Ocean Sciences
  5. Directorate For Geosciences [0910624] Funding Source: National Science Foundation

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Diatoms are photoautotrophic organisms capable of growing on a variety of inorganic and organic nitrogen sources. Discovery of a complete urea cycle in diatoms was surprising, as this pathway commonly functions in heterotrophic organisms to rid cells of waste nitrogen. To determine how the urea cycle is integrated into cellular nitrogen metabolism and energy management, the centric diatom Thalassiosira pseudonana was maintained in semi-continuous batch cultures on nitrate, ammonium, or urea as the sole nitrogen source, under a 16: 8 light: dark cycle and at light intensities that were low, saturating, or high for growth. Steady-state transcript levels were determined for genes encoding enzymes linked to the urea cycle, urea hydrolysis, glutamine synthesis, pyrimidine synthesis, photorespiration, and energy storage. Transcript abundances were significantly affected by nitrogen source, light intensity and a diel cycle. The impact of N source on differential transcript accumulation was most apparent under the highest light intensity. Models of cellular metabolism under high light were developed based on changes in transcript abundance and predicted enzyme localizations. We hypothesize that the urea cycle is integrated into nitrogen metabolism through its connection to glutamine and in the eventual production of urea. These findings have important implications for nitrogen flow in the cell over diel cycles at surface ocean irradiances. (C) 2011 Elsevier GmbH. All rights reserved.

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