Research themes

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Biological nitrogen fixation by canonical and alternative nitrogenase metalloenzymes

The global nitrogen cycle has been profoundly disturbed by industrial fertilizer production, resulting in an enhancement of global warming, air and water pollution, and biodiversity loss. Biological nitrogen fixation, catalyzed by the microbial metalloenzyme nitrogenase is nature's original solution to fertilizer production and is a key parameter used to estimate human disruption of the nitrogen cycle. We know little of the rates and controls on environmental N2 fixation by different trace metal forms of nitrogenase. This affects our understanding of ecosystem fertility as well as strategies to manage food and energy supplies. At Princeton, we have developed new methods that distinguish the activity of canonical Mo- and alternative V- and Fe-only nitrogenases and are applying these methods to better understand the controls on environmental N2 fixation at scales ranging from metabolites to ecosystems.

Related papers:

Zhang X., McRose D. L., Darnajoux R., Bellenger J.-P., Morel F.M.M., Kraepiel. A.M.L. (2016) Alternative nitrogenase activity in the environment and nitrogen cycle implications. Biogeochemistry. DOI: 10.1007/s10533-016-0188-6

Zhang X., Sigman, D.M., Morel F.M.M., and Kraepiel A.M.L. (2014) Nitrogen isotope fractionation by alternative nitrogenases and past ocean anoxia. PNAS 111(13):4782-4787. DOI: 10.1073/pnas.1402976111

Bellenger J.P., Xu Y., Zhang X., Morel F.M.M., and Kraepiel A.M.L. (2014) Possible contribution of alternative nitrogenases to nitrogen fixation by asymbiotic N2-fixing bacteria in soils. Soil Biology and Biochemistry 69(0):413-420. DOI: 10.1016/j.soilbio.2013.11.015

Trace metal acquisition, an essential process for metalloprotein function

The acquisition of essential trace metals is a fundamental requirement for metalloprotein function but is often a challenge for microbes: Too low a concentration results in suboptimal uptake but too high a concentration of any metal (including essential metals) is toxic. Microbes cope by releasing strong metal binding secondary metabolites that control metal uptake. Despite their importance as "gatekeeper" metabolites, our knowledge of biogenic metal chelators is limited. At Princeton, I work in collaboration with analytical chemists to understand the diversity of strategies bacteria use to obtain essential trace metals.

Baars O, Zhang X., Morel F.M.M., Seyedsayamdost M. (2015) The siderophore metabolome of Azotobacter vinelandii. Applied and Environmental Microbiology DOI: 10.1128/AEM.03160-15

Metabolic impacts on the hydrogen stable isotope content of bacterial lipids

Related papers:

Zhang X., Gillespie A. L., and Sessions A.L. (2009) Large D/H variations in bacterial lipids reflect central metabolic pathways. PNAS 106:12580-12586. DOI: 10.1073/pnas.0903030106

Energy flow in symbiotic microbial systems

Related papers:

Rosenthal A.Z.*, Zhang, X.*, et al. (2013) Localizing transcripts to single cells suggests an important role of uncultured deltaproteobacteria in the termite gut hydrogen economy. PNAS 110 (40): 16163-16168 *equal contributors. DOI: 10.1073/pnas.1307876110

Matson E.G., Rosenthal A.Z., Zhang X., and Leadbetter J.R. (2013) Genome-wide effects of selenium and translational uncoupling on transcription in the termite gut symbiont Treponema primitia. mBio 4(6) DOI: 10.1128/mBio.00869-13

Zhang X., and Leadbetter J.R. (2012) Evidence for cascades of perturbation and adaptation in the metabolic genes of higher termite gut symbionts. mBIO 3(4): e00223-12. DOI: 10.1128/mBio.00223-12

Zhang X., Matson E.G., and Leadbetter J.R. (2011) Genes for selenium dependent and independent formate dehydrogenase in the gut microbial communities of 3 lower, wood-feeding termites and a wood-feeding roach. Environmental Microbiology 13(2): 307-323. DOI: 10.1111/j.1462-2920.2010.02330.

Matson E.G., Zhang X., and Leadbetter J.R. (2010) Selenium controls transcription of paralogous formate dehydrogenase genes in the termite gut acetogen, Treponema primitia. Environmental Microbiology 12: 2245-2258. DOI: 10.1111/j.1462-2920.2010.02188.x

Warnecke F., et al. (2007) Metagenomic and functional analysis of hindgut microbiota of a wood-feeding higher termite. Nature 450: 560-565. DOI: 10.1038/nature06269