Dr. Erik Zinser

See Also: Curriculum Vitae

Major Research Interests

The primary focus of this group is to explore the relationships between physiology, ecology, and the forces of selection.  We use a combination of field ecology and laboratory experimentation to explore adaptation in natural microbial populations and in cultured representatives of those populations.  Our current interests are aimed at understanding how temperature and the presence of other microbes influences Prochlorococcus physiology and distribution in nature.

Temperature and Prochlorococcus ecophysiology

While it is becoming clear that microbes are highly diverse, less clear is the ecological consequence of that genetic variation.  A great challenge in microbial ecology is therefore to differentiate between “meaningful” variation (ecological determinants) and noise (neutral mutations).  The system we use to explore this diversity is the unicellular cyanobacterium Prochlorococcus, which is the most abundant photosynthetic organism in the oceans, and as such is a major player in the Earth’s biogeochemical cycles.  What the research community has learned is that different genetic lineages (i.e. ecotypes), with corresponding differences in physiology, occupy different niches in the ocean. For instance, some lineages are genetically predisposed to grow optimally at high light, and these are generally found higher in the water column (i.e. closer to the sun) than those predisposed to grow optimally at lower light.

Our attention is currently focused on temperature as an ecological determinant that further differentiates the ecotypes of Prochlorococcus.   We collaborate on this National Science Foundation-funded project with Dr. Zackary Johnson’s group at the University of Hawaii.  Prior work by Johnson and Zinser, during their postdoctoral fellowships with Penny Chisholm at MIT, established that the two numerically-dominant ecotypes of Prochlorococcus in the Atlantic Ocean partition the niche based on their temperature optima: eMIT9312 is dominant in the low latitudes, consistent with its superior growth at high temperatures, while the eMED4 ecotype is dominant at the high latitudes, consistent with its superior growth at low temperatures (Johnson et al., 2006).  One of our recent travels has taken our groups to the Western Pacific Warm Pool, due east of New Guinea.  This region is the hottest body of water in the open ocean, with temperatures exceeding 30 °C.  Those interested in our Hawaii to Brisbane, Australia transect that took us to the Warm Pool are invited to check out our cruise web page, which includes photos and a daily journal of the 40-day voyage.  In total, 8 students and faculty from the Microbiology Department at UT participated in this cruise, including members of Steven Wilhelm’s and Alison Buchan’s labs.  We are particularly interested in the types of Prochlorococcus we find at the Warm Pool: are they especially-adapted to warm temperature?  What can they tell us about the ecology of the oceans if climate change results in elevated temperatures in other parts of the ocean?

Prochlorococcus – heterotroph interactions

In the oceans, Prochlorococcus is part of a large and diverse microbial community, and we have discovered that it does not like being alone.  Prior attempts to grow colonies from single cells on agar plates or to grow liquid cultures from dilute inoculations met largely with failure.  However, when we pre-seeded the agar medium with heterotrophic bacteria, Prochlorococcus colonies formed at very high success rate (Morris et al., 2008).  This “helping phenomenon also occurs in liquid media, in ecologically-relevant concentrations of Prochlorococcus and heterotrophic bacterium.  Furthermore, once the Prochlorococcus population crosses a threshold (approx. 1 million cells per milliliter) it no longer requires the presence of heterotrophic bacteria, which can then be eliminated by the use of antibiotics.  This has provided us with a means to obtain clonal Prochlorococcus in the first step, and then axenic (pure) cultures of the clonal population in the second step.  Currently, we are using this protocol to purify the existing collection of Prochlorococcus isolates, and to obtain axenic cultures of new isolates from the oceans.   

The second focus of this project is to understand the molecular and physiological basis of this “helping” phenotype of the heterotrophic bacteria.  Genetic and biochemical evidence points to reactive oxygen species, such as hydrogen peroxide, playing an important role in this relationship.  Prochlorococcus is particularly prone to oxidative stress, and our data thus far indicate that the heterotrophic bacteria help Prochlorococcus by eliminating reactive oxygen species from the growth medium.

The third focus of this project is to tie this laboratory phenomenon to natural communities in the ocean.  Microbes are the primary “sink” for hydrogen peroxide in the oceans, and we are currently testing the hypothesis that this sink is essential for the persistence of Prochlorococcus in these marine systems.

Lab members (from left): Jeremy Chandler, Marty Szul, Robin Kirkegaard, Jeff Morris, Erik Zinser

Dr. Erik Zinser

Assistant Professor
Ph. D., 2001
Harvard University

M409 Walters Life Sciences
Knoxville, TN 37996-0845

Phone: 865-974-9283
Fax: 865-974-4007
Email: ezinser@utk.edu