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


Tyler Coale

Postdoctoral Scholar

I investigate the physiology and ecology of eukaryotic marine phytoplankton and their interactions with associated microbes. Of particular interest are the adaptations of marine phytoplankton to the low nutrient conditions typical of the open ocean. These include acquisition proteins, intracellular trafficking, diverse strategies to improve nutrient use efficiency, and microbial partnerships mediated by nutrient bioavailability. My research involves the replication of environmental conditions in the lab in order to connect cellular functioning to the understanding of biogeochemical processes.   


Prior to joining the Zehr lab, I obtained a BS in Plant Sciences from the University of California, Santa Cruz. I worked in the chemical oceanography labs of Kenneth Bruland at UCSC and Kristen Buck at the Bermuda Institute of Ocean Sciences. In 2020 I received my PhD from Scripps Institution of Oceanography under the supervision of Andrew Allen, and subsequently worked as a postdoctoral fellow at the J. Craig Venter Institute in La Jolla, CA.


email Tyler: 

tcoale AT ucsc DOT edu


Michael (Mo) Morando

Postdoctoral Scholar

email Mo: 

mmorando AT ucsc DOT edu


Esther Mak

Graduate Student

e-mail Esther:

wimak AT ucsc DOT edu


Anna Voznyuk

Undergraduate researcher

Currently I am helping in determining the optimal temperatures in cultivating unicellular cyanobacterial diazotrophs (culture transfers and taking and running samples through the cytometer) along with other miscellaneous laboratory work. In my time with this research group, I hope to learn how biotic and abiotic environmental factors influence the behaviour of diazotrophs and how evolutionarily such responses came to be. Furthermore, I wish to someday understand how/if those responses are beneficial in terms of the species' survival and the nitrogen cycle and apply the findings to the outlook of the future of our oceans. In the future I aspire to become a researcher in the field of evolutionary genetics focusing on cellular communication but as of now am still on the search for the right "why?" question to guide me.

e-mail Anna:

avoznyuk 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