NAI
2010 Annual Science Report
Arizona State University
Reporting | SEP 2009 – AUG 2010
Stoichiometry of Life - Task 1d - Experimental Studies - the Role of Molybdenum in the Nitrogen Cycle, Past and Present
Project Summary
The element molybdenum (Mo) is critical for key processes in the cycling of nitrogen (N); for example, it is essential for the enzyme nitrogenase which bacteria use to convert gaseous N to “fixed” N that can be used in biological processes. This project seeks to understand how Mo might limit N processing in modern ecosystems (lakes and oceans) and infer its potential role in the past.
Project Progress
Mo storage protein Mop in cyanobacteria: Graduate Student Jennifer Glass, Postdoctoral Fellow Felisa Wolfe-Simon, James Elser and Ariel Anbar published research on molybdenum (Mo) requirements for nitrogen fixation and evidence of Mo storage in freshwater heterocystous cyanobacteria in early 2010 in Limnology & Oceanography (Glass et al., 2010). In order to determine the regulation of the putative Mo storage protein “Mop” in freshwater heterocystous cyanobacteria, Glass and undergraduate research assistant Eric Hughes performed more experiments in February 2010 with the model organism Nostoc sp. PCC 7120 under three treatment conditions: low Mo (1 nM), medium Mo (150 nM) and high Mo (3000 nM). All of the treatments were grown without added nitrogen so that they were forced to fix nitrogen from the atmosphere using the molybdenum-dependent enzyme nitrogenase. In short-term experiments (four transfers/17 days), we found that transcription of mop and nifD is up-regulated when Mo is low (~1 nM). However there is minimal Mop protein present in the same samples, suggesting that post-transcriptional regulation maintains low levels of Mop protein at low cellular Mo (<5ppm). It is possible that proteases preferentially degrade Mop in its apo-form. Mop was present in cultures grown at higher Mo, and in previously Mo-limited cultures 5 days after addition of 3000 nM Mo. In contrast, NifD protein levels were elevated at 1 nM Mo compared to other treatments. Our findings support Mop’s role as a Mo storage protein in heterocystous cyanobacteria and suggest that cyanobacteria maintain Mo cellular homeostasis by sensing Mo at the post-transcriptional level. These results will be submitted to the journal Applied and Environmental Microbiology.
Mo-nitrate co-limitation at Castle Lake: To explore the Mo requirements for nitrate assimilation of freshwater planktonic and microbial communities, Glass performed incubation experiments during the summers of 2008 and 2009 at the low-Mo ecosystem of Castle Lake, northern California. In situ bottle incubations with Mo and nitrate added singularly or in combination were performed at three depths (3, 15 and 25 meters). Addition of Mo stimulated nitrate assimilation in the Castle Lake hypolimnion in 2008 and in the epilimnion in 2009. Interannual and depth response differences were explained by ammonium inhibition of nitrate uptake and seasonal succession of plankton species with differing Mo requirements. Both summers a dissolved Mo minimum was observed in the Castle Lake epilimnion, which was likely a result of strong Mo draw-down by nitrogen-fixing periphyton communities in the littoral zone. Laboratory chemostat experiments with a common freshwater green alga, Scenedesmus acutus, confirmed that low Mo (1 nM) severely depressed activity of the Mo-containing enzyme nitrate reductase when nitrate was the sole nitrogen source. This study lends further support to the theory that low Mo can limit nitrate assimilation in freshwaters with typical low Mo levels (<5 nM) when ammonium is scarce, possibly resulting in decreased capacity of terrestrial ecosystems to serve as sinks for anthropogenic carbon dioxide emissions. A paper on this research is currently in review in the journal Biogeochemistry. Another paper on the geochemistry of Mo cycling in Castle Lake is in preparation for the journal Geochimica Cosmochimica Acta.
Publications
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Glass, J. B., Axler, R. P., Chandra, S., & Goldman, C. R. (2012). Molybdenum limitation of microbial nitrogen assimilation in aquatic ecosystems and pure cultures. Frontiers in Microbiology, 3. doi:10.3389/fmicb.2012.00331
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Godfrey, L. V., & Glass, J. B. (2011). The Geochemical Record of the Ancient Nitrogen Cycle, Nitrogen Isotopes, and Metal Cofactors. Methods in Enzymology, None, 483–506. doi:10.1016/b978-0-12-381294-0.00022-5
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- Glass, J.B. & McGlynn, S.E. (2010). How do life and global geochemical cycles mutually affect each other? Astrobiology Primer, 2.0(4.2.3): In preparation.
- Glass, J.B., Boyd, E.S., Romaniello, S. & Anbar, A.D. (2010). Evolutionary metallomics: A nickel for nitrogenase. Nature Geoscience.
- Glass, J.B., Chandra, S., Elser, J.J. & Anbar, A.D. (2010). Molybdenum limitation of nitrate assimilation in Castle Lake, California. ASLO-NABS Joint Meeting. Santa Fe, NM.
- Glass, J.B., Chappaz, A., Eustis, B., Heyvaert, A.C., Waetjen, D. & Anbar, A.D. (2010). Identifying major sources of molybdenum to Castle Lake, California: anthropogenic vs. natural inputs. Geochimica Cosmochimica Acta.
- Glass, J.B., Hamilton, G.A., Hartnett, H.E., Mestek, R.L., Morgan, J.L.L., Noonan, K.M., Shipp, J.A., Raiswell, R. & Anbar, A.D. (2010). Growth of an Artic diatom with nanoparticulate iron: implication for the supply of bioavailable iron from icebergs. Marine Chemistry.
- Glass, J.B., Wolfe-Simon, F., Poret-Peterson, A.T. & Anbar, A.D. (2010). Regulation of Mop, a molybdenum storage protein, in the cyanobacterium Nostoc PCC 7120. Applied and Environmental Microbiology.
- Glass, J.B., Wolfe-Simon, F., Poret-Peterson, A.T., Hughes, E.D. & Anbar, A.D. (2010). Post-transcriptional regulation of Mop expression by molybdenum. 7th International BioMetals Symposium.
- Glass, J.B., Wolfe-Simon, F., Poret-Peterson, A.T., Hughes, E.D. & Anbar, A.D. (2010). Regulation of mop gene expression by Mo in heterocystous cyanobacteria: Signatures of Mo-limited photosynthesis in the ocean before 800 Ma? 7th Annual Southern California Geobiology Symposium. California Institute of Technology.
- Glass, J.B., Wolfe-Simon, F., Poret-Peterson, A.T., Hughes, E.D. & Anbar, A.D. (2010). Signatures of low-Mo ancient ocean may be preserved in cyanobacterial genomes. AbSciCon. League City, Texas.
- Glass, J.B., Wolfe-Simon, F., Poret-Peterson, A.T., Hughes, E.D. & Anbar, A.D. (2010). Transcriptional and translational controls on molybdenum regulation of mop expression. Environmental Bioinorganic Chemistry Gordon Research Conference.
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PROJECT INVESTIGATORS:
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PROJECT MEMBERS:
Eric Boyd
Collaborator
Anthony Chappaz
Collaborator
Felisa Wolfe-Simon
Collaborator
Eric Hughes
Undergraduate Student
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RELATED OBJECTIVES:
Objective 4.1
Earth's early biosphere.
Objective 5.1
Environment-dependent, molecular evolution in microorganisms
Objective 6.1
Effects of environmental changes on microbial ecosystems
