Zehr Lab Personnel


Jonathan P. Zehr

Distinguished Professor of Ocean Sciences

Isaac profile pic.png

Isaac Shunyan Cheung

Postdoctoral Scholar

Research interests: 

  • Biogeographies, ecophysiologies and functions of microorganisms (mainly nitrogen and carbon fixers) in marine ecosystems  

  • Responses of marine nitrogen and carbon cycles to the global climate change 


I am currently investigating the nitrogen fixation contribution, physiological features and environmental determinants of the poorly understood non-cyanobacterial diazotrophs in the ocean, using single-cell and omics approaches.  

email Issac: 

scheun16 AT ucsc DOT edu

Link to Issac's Research Gate Profile


Mary Rose (Rosie) Gradoville

Postdoctoral Scholar

I am interested in the diversity, activity, and ecology of marine microorganisms, especially nitrogen-fixing bacteria. My research in the Zehr lab is based on the “Gradients” research project, in which a team of scientists are mapping the gradients in diversity and productivity between the North Pacific Subtropical Gyre and the North Pacific Subarctic Gyre. For this project, we departed Honolulu and sailed over 1000 miles north, collecting physical, chemical, and biological samples. I am exploring how the diversity and activity of marine nitrogen-fixers changed along this journey from the warm, clear Hawaiian waters—a classical habitat for nitrogen fixation—to the colder, more nutrient-rich waters of the subarctic North Pacific. My research uses DNA and RNA sequence analyses, fluorescence-based cell sorting, and single-cell nitrogen fixation rate measurements. 


email Rosie: 

mgradoville AT ucsc DOT edu

Link to Rosie’s Google Scholar Citations

Link to Rosie’s Research Gate Profile


Michael (Mo) Morando

Postdoctoral Scholar

email Mo: 

mmorando AT ucsc DOT edu


Esther Mak

Graduate Student

e-mail Esther:

wimak AT ucsc DOT edu


Britt Henke

Associate Specialist

I am interested in researching and communicating the important work of marine nitrogen (N2) fixing bacteria, especially the unique and ubiquitous Unicellular Cyanobacteria group-A (UCYN-A). N2-fixing bacteria support primary production by supplying nitrogen (N) to the vast oligotrophic areas of the world’s oceans. In this way N2-fixing bacteria effect global nutrient cycles and support phytoplankton oxygen production, which accounts for half of all the oxygen we breathe! By communicating our interdependence with marine microbes, I hope to inspire scientific understanding and inquiry including broad acceptance of and honest discussion about human-induced climate change. In my capacity as a Lab Specialist I do science, support the research of graduate students and postdocs, mentor undergraduates, and generally keep the lab running, including ensuring that our lab is a safe and friendly working environment for all.

e-mail Britt:

bhenke AT ucsc DOT edu


Jonathan Magasin 


My goal is to improve our understanding marine microbial communities in their natural environments.  To this end, I enjoy creating software tools to help analyze large data sets derived from marine environmental samples (metagenomic and metatranscriptomic) produced by next-generation sequencing and our MicroTOOLs microarray.  I am also interested in how the staggering number of public marine environmental data sets archived in "omics" repositories can be used to discover marine microbes that are widespread but have been overlooked due to biases toward studying cultivable types.

email Jonathan:  

jmagasin AT ucsc DOT edu


Kendra Turk-Kubo

Project Scientist

My current research focuses on understanding the environmental factors driving the diversity, biogeography and activity of marine nitrogen-fixing microbes. Vast areas of the sunlit surface ocean have no detectable nitrogen, yet are teeming with microbial life. Life in these “ocean deserts” is made possible, in part, by microbes that are able to convert dinitrogen (N2) gas into biomass through the process of N2 fixation. This process has been known to be important in the marine environment for several decades now, yet we are still in the early stages of understanding the organisms responsible. Many N2-fixers have yet to be isolated in culture, so my research relies on applying cultivation independent techniques to detect and study these cryptic microbes. I am involved in multiple collaborative research projects funded by the National Science Foundation (NSF), the Gordon and Betty Moore Foundation (GBMF) and the Simons Foundation. My research goals within these projects are focused on: 1) Identifying the quantitative significance of a unique N2-fixer that lives in symbiosis with another single-celled algae (UCYN-A/haptophyte symbiosis) to N budgets in coastally-influenced marine waters; 2) Determining the environmental controls on N2 fixation in the UCYN-A symbiosis, and how their activity may be linked to the composition and activity of the broader microbial community in the North Pacific; 3) Adapting  super resolution ion beam imaging (srIBI) to enable localization and imaging of subcellular structures and characterization of metabolic exchanges in aquatic symbioses; and 4) Determining whether non-cyanobacterial microbes with the genetic capability to fix N2 are active and important marine N2-fixers to gain a better understanding of whether these organisms should be considered in ecological models of marine N2 fixation. 


e-mail Kendra:

kturk AT ucsc DOT edu

Link to Kendra's Google Scholar Citations

Link to Kendra's Research Gate Profile