I am an environmental microbiologist in François Morel's trace metal research group in the Geosciences department at Princeton University. I obtained a B.S. in Biological & Environmental Engineering from Cornell University in 2004 and a Ph.D. in Environmental Science & Engineering from the California Institute of Technology in 2010.
I am interested in how microbes modulate nutrient and energy flows in the environment. Metalloproteins are a central feature of my research as they catalyze nearly all energy transfers in biology. Yet, we know little about the factors that control their activities in the environment, greatly limiting our ability to understand and address human-induced changes in climate, elemental cycling, and the energy landscape. To study the function and evolution of key microbial metalloproteins within terrestrial carbon and nitrogen cycles, I develop and apply interdisciplinary tools to research in both laboratory and field settings.
Ongoing Research Projects:
Controls on N2 fixation by nitrogenase metalloenzymes, nature's original sources of fertilizer: 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 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, I have developed new methods that distinguish the activity of Mo, V, and Fe-only nitrogenases and am applying these methods to better understand controls on environmental N2 fixation at scales ranging from metabolites to ecosystems.
- 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.
- 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.
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 (O. Baars, M.Seyedsayamdost) to understand the diversity of strategies bacteria use to obtain essential trace metals.
Previous Research Projects:
Metabolic impacts on the hydrogen stable isotope content of bacterial lipids.
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.
Diversity and evoluton of a key enzyme used for H2 transfer by lignocellulose-degrading insect gut microbiota
- 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 *equal contributors
- 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).
- 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.
- 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.
- 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.
Princeton University, Department of Geosciences, 152 Guyot Hall, Princeton NJ 08544
Phone: (609) 258-2489