Research

Ecotypic diversity and adaptation of Prochlorococcus in the stratified high temperature waters of the Western Pacific Warm Pool (NSF Funded Project) - collaboration with Erik Zinser (University of Tennessee)

In most tropical and subtropical ecosystems, the prokaryotic cyanobacteria Prochlorococcus plays a critical role in ecosystem structure and biogeochemistry because it is the numerically dominant photoautotrophic picoplankter. Although the worldwide distributions of Prochlorococcus are generally understood, the precise reasons for its overwhelming ecological success have remained elusive. This picture has recently become complicated by the discovery that Prochlorococcus is not monophyletic and that different genetic clades of Prochlorococcus have remarkably different distributions with depth and over oceanic basins. Thus, our understanding of factors that structure Prochlorococcus populations in the natural environment, and our ability to predict how this structure might respond to environmental changes, are limited. The PIs will address this by focusing on naturally occurring populations in the Western Pacific Warm Pool, an area where Prochlorococcus is known to dominate, but where there are no data on clade abundances. In addition to being a large region of the Pacific Ocean with significance to the global carbon cycle, the Western Pacific Warm Pool (WPWP) is of particular interest because it is typically highly stratified, with surface waters having extreme temperatures and light levels compared to those at depth. Populations of Prochlorococcus at the surface and at depth experience different environmental pressures, and may belong to different clades and have different adaptive physiologies. The PIs will test this hypothesis on a cruise from Hawaii to New Castle, Australia through the stratified WPWP. Samples from this transect will be used to quantify (using quantitative PCR) the six known clades of Prochlorococcus and to search for new clades (using clone libraries and isolates) and their abundances. The ultimate goal is to relate clade abundances to temperature, light, nutrient concentrations and other measured biological, chemical and physical variables. This project will encompass multiple layers of outreach to scientists and the scientific community at large. Data and strains will be deposited at national repositories and results will be disseminated through publications, professional meeting presentations, and a project web site. Undergraduates and graduate students will be trained, and students will be an integral part of the data collection, analysis, and dissemination phases and will be encouraged to present at national meetings. Cross-institutional training will enhance graduate student education. The PIs will integrate results from this project into undergraduate and graduate curricula at their home institutions and will be attending the NSF sponsored 'Scientific Inquiry in the K-16 Classroom' seminar to develop methods to link results to primary education. The PIs will use presentations and activities with local outreach groups, such as the Hawaii Academy of Sciences, to encourage scientific understanding through mentoring, science symposia and science competitions for primary and secondary school students.

Iron light co-limitation in the deep chlorophyll maximum of stratified oceanic regimes (NSF Funded Project) - collaboration with Katherine Barbeau (Scripps) and Elizabeth Mann (Skidaway)

Researchers from Scripps Institute of Oceanography, the University of Hawaii, and Skidaway Institute of Oceanography plan to test the hypothesis that iron-light co-limitation at the deep chlorophyll maxima (DCM) is a widespread feature of oceanic stratified euphotic zones, and an important control on phytoplankton community composition and size structure. Three different types of DCM will be investigated: mesotrophic, relatively shallow maxima, deeper, chlorophyll per cell based DCM characteristic of oligotrophic gyres, and the Prochlorococcus maximum found just below the oxic/suboxic boundary in the Eastern Tropical North Pacific. To attain their goals, the scientists will carry out the following tasks during the cruises: (1) characterize water column parameters including basic hydrography, nutrient distributions, iron concentration and speciation, phytoplankton community structure, and primary productivity and photosynthetic efficiency; (2) conduct co-limitation incubation experiments at the three types of DCMs; and (3) determine picoplankton cell division and grazing rates. As regards broader impacts, the researchers plan to recruit undergraduates from both the University of California-San Diego and from an historically black college or university such as Savannah State University via the Collaborations in Integrating Research and Education Program using Research Experience for Undergraduates supplemental funds. A science teacher from California and one from Georgia will be asked to participate in research cruises using supplemental funds from Research Experiences for Teachers. Both teachers will be expected to produce educational materials based on their field experiences. One graduate student from the University of California-San Diego, one from the University of Hawaii and one from Skidaway Institute of Oceanography will be trained and supported as part of this study.

Two massive bacterial 16S rRNA clone libraries from the oligotrophic Pacific Ocean (JGI - DOE Funded Project) - collaboration with Matthew Church (UH), Dave Karl (UH), Mike Rappe (UH)

In the open ocean microbes dominate biogeochemical processes, including carbon cycling and energy flow. Oceanic microbial communities are estimated to be genetically diverse, with major classes of prokaryotes still being discovered. To date however, there exists no direct estimate of bacterial diversity richness (the number of unique individuals) from a pelagic ocean site, partly because the richness of these assemblages is estimated to be extreme and the task daunting. This unexplored diversity likely harbors entire clades of novel bacteria that perform significant biogeochemical transformations and thus influences our understanding of oceanic food webs and biogeochemical fluxes. Here we seek to constrain the estimate of eubacterial community richness in the open ocean by constructing and sequencing two large (20,000 member - equivalent to ~6X coverage of the average bacterium) SSU rRNA gene clone libraries from the oligotrophic Pacific Ocean . Our sampling will be from the euphotic and “twilight” zones of station ALOHA, a representative oceanic site located ~100km north of Oahu , where the Hawaiian Ocean Time-series (HOT) has been conducting continuous monthly sampling of numerous biogeochemical and microbial variables for the last 18 years. Such data provides a robust temporal characterization of the biogeochemical context of the bacterial community. The specific goals for creating and analyzing the clone libraries are (1) to constrain the estimate of eubacterial diversity richness in the pelagic Pacific Ocean in two environments dominated by different bacterial assemblages and with different roles in carbon cycling, (2) to potentially discover new clades of eubacteria that may be performing important and possibly novel biogeochemical transformations (either new classes within known groups (ex. Prochlorococcus spp.) or entirely new groups) (3) to robustly compare the eubacterial community assemblages between the epipelagic (carbon consuming) and mesopelagic (carbon respiring) zones of the water column and (4) to create a SSU rRNA sequence database and clone collection to serve as a community resource for future studies of marine eubacterial diversity and function. The insights gained from this study will complement current genomic studies at HOT (ex. BAC and shotgun sequencing) and have the potential to significantly affect future studies of the abundance, distribution and biogeochemical contributions of marine microbes to food webs and biogeochemical fluxing.