Dr. Adam Kustka, Assistant Research Professor

Institute of Marine and Coastal Sciences
Rutgers, The State University of New Jersey
71 Dudley Road
New Brunswick, NJ 08901
Phone: (732) 932-6555 x 236
Fax: (732) 932-4083

kustka@marine.rutgers.edu

Current Research Interests

Phytoplankton Trace Metal Physiology and Biogeochemistry

I am working towards understanding the factors that govern the relative success of various phytoplankton in the ocean. I am most interested in differences in nutrient physiology among phytoplankton taxa, how these differences translate into niche differentiation, and the impact of these differences on biogeochemical cycling of macro- and micronutrients. A second goal of my research is to achieve a quantitative, mechanistic, understanding of how organisms either decrease their requirements or increase nutrient availability. Since the capacity of an organism to acquire limiting resources or to economize on the cellular demand contributes to its competitive fitness, I believe this approach will ultimately contribute towards a more comprehensive understanding of factors constraining ecosystem-level processes (especially as more genomes of marine organisms are sequenced).

Most of my work to date has involved various aspects of the micronutrient iron – how phytoplankton acquire iron and how much they need to fuel Fe-intensive processes such as N₂ fixation (see my CV). A hallmark of my work has been the use of interdisciplinary approaches rooted in phytoplankton ecology, physiology, field-based oceanography, aquatic and analytical chemistry and modern molecular techniques.

I am currently working on a project funded by Kay Bidle (here at IMCS) and John Reinfelder (in the Dept. of Environmental Sciences) to elucidate the molecular underpinnings of the 4-carbon organic acid (“C4”) route of CO₂ concentrating mechanisms in diatoms#. We have documented the rapid up-regulation of gene transcripts that may encode for “C4-type” proteins upon a shift from high to low pCO₂ and are following this up with detailed physiological studies.

I have also recently been awarded two NSF proposals that include four lines of student support. Contact me (kustka@imcs.rutgers.edu) for updates on these STUDENT FUNDING OPPORTUNITIES.

1) “Collaborative Research: Iron storage in diatoms and N2 fixing cyanobacteria: mechanisms, regulation and biogeochemical significance”. A. Kustka (PI) and Benjamin Twining (Co-PI). Funded by NSF Ocean Sciences, Biological Oceanography.

Studies on the Fe physiology of phytoplankton have primarily focused on the induction of high affinity uptake pathways or the rearrangement of photosynthetic machinery to decrease the cellular demand, but very little attention has been given to the mechanisms of intracellular Fe storage. Proper handling and storage of Fe on timescales of generations can ensure adequate Fe nutrition in episodic environments and short term storage of Fe is essential to “buffer” the intracellular redox-labile Fe concentration and prevent Fenton production of reactive oxygen species. Our understanding of Fe storage lags far behind what is known for C, N and P, despite that sufficient Fe can be stored for at least 4 cell divisions, much more than in the cases of P, N and (especially) C. Since the biogeochemical cycles of Fe and C, N and P are linked via the Fe quotas of phytoplankton, it is critical that we understand the environmental and physiological controls on this parameter. We propose to address questions related to Fe storage using a combination of Synchrotron X-Ray Fluorescence measurements of intracellular metal distribution, molecular biological approaches, and trace metal clean phytoplankton culturing and field techniques.

Fe can be stored in proteins such as those of the ferritin superfamily or sequestered into intracellular vacuoles. Some marine diatoms, such as Phaeodactylum tricornutum have ferritin genes, while ferritin has not been detected bioinformatically or by evolutionary PCR methods in other diatoms such as Thalassiosira pseudonana. We have measured the Fe-dependent regulation of transcript and protein abundance of NRAMP, a protein likely involved in vacuolar Fe metabolism, which is an alternative method of Fe storage found in Arabidopsis thaliana and yeast. We propose the regulation and biogeochemical significance of ferritin and vacuole-mediated Fe storage may differ, reflecting the obvious difference in mechanism. From a geochemical perspective, the form at which Fe is stored may dictate the biogeochemical fate of Fe in seawater. After viral lysis or grazing events, the ferritin-bound Fe may be quite refractory to dissolution. We do not yet have any information on the speciation of vacuole-bound Fe, although we suspect it is as Fe(II).

Trichodesmium, an N₂ fixing cyanobacterium, may have three genes for ferritin, a peculiar attribute for a prokaryote. We hypothesize one or more of these proteins serve as an Fe reservoir over long, generational, time scales – in which case they may be an indicator of nutritional Fe status. We also hypothesize that one or more of these proteins are co-localized in cells specifically responsible for N₂ fixation in Trichodesmium colonies as a mechanism to buffer the Fe released through the diel degradation of the Fe-rich nitrogenase proteins. We will address the above objectives using genetic, immunological, and synchrotron-based approaches applied to laboratory cultures of P. tricornutum, T. pseudonana, and Trichodesmium. We will also analyze Trichodesmium trichomes collected from the Sargasso Sea in order to determine the biogeochemical importance of (bacterio)ferritins as a storage mechanism in this group.

2) “Collaborative research: Expression profiling and functional genomics of a pennate diatom: mechanisms of iron acquisition, stress acclimation, and recovery”. Andrew Allen (PI) and A. Kustka (Co-PI). Funded by NSF Ocean Sciences, Biological Oceanography.

We propose to capitalize on the extremely well annotated Phaeodactylum tricornutum genome sequence in order to characterize global patterns of gene expression in response to shifts into and out of Fe and N stress and over the course of a diel cycle. Our primary goal is to determine the molecular and physiological processes that constrain and define different phases and levels of Fe-stress acclimation. Oceanic physiological regimes have recently been defined by Behrenfeld and colleagues according to different combinations of Fe and N availability and physiological indicators of the resident phytoplankton. The proposed research will provide molecular-level insights into defense, acclimation, and regulatory mechanisms and pathways that govern critical survival strategies in oceanographically-relevant stress situations. Our EST and partial genome microarray data, for example, indicate that chaperones and proteases play a very significant role in monitoring cellular health and balancing the difference between investment in defense or activation of programmed cell death (PCD) under Fe limitation. The proposed research will provide novel insights into the regulation of this balance. Basic cellular processes such as this play an important biogeochemical role in controlling bloom dynamics and regulating particle flux. We will combine analysis of global gene expression with state of the art monitoring of intracellular metal levels and primary metabolite profiles using ICP-MS and gas chromatograph-mass spectroscopy (GC-MS) in order to gain novel insights into basic factors that determine cell survival.

Fe bioavailability to marine eukaryotic phytoplankton continues to be a nebulous and poorly understood phenomenon at the mechanistic level, despite the clear role of Fe in limiting phytoplankton growth in vast expanses of the ocean. About 84 and 16% of dissolved Fe in seawater is complexed to either strong or weak organic ligands (the so-called L₁ and L₂ classes) that have similar conditional stability constants as siderophores and heme bound Fe. We will evaluate P. tricornutum transcriptome profiles resulting from exposure to Fe-hydroxamate siderophores and heme-bound Fe in order to understand the network of genes specifically involved in recognizing and assimilating these compounds. An advanced reverse-genetics system for manipulating levels gene expression in P. tricornutum will be used to evaluate the specific role of particular genes and pathways in Fe uptake from these ligands.

I am also currently participating in manual genome annotation efforts in the whole genome sequencing of two marine phytoplankton species. Aureococcus anophagefferens, the so called “Long Island Brown Tide” has decimated the scallop fishery on Long Island, N.Y. and has unique physiological adaptations that may have allowed it to periodically dominate shallow embayments of Long Island (check out http://www.state.nj.us/dep/dsr/browntide/bt.htm). Emiliania huxleyi is a cosmopolitan oceanic phytoplankton species that forms calcium carbonate shells (“coccoliths”) around each cell. This process has major implications for seawater chemistry and global carbon biogeochemistry http://www.soes.soton.ac.uk/staff/tt/ . Over hundreds of millions of years, the sinking and burial of trillions of these cells has lead to the formation of CaCO₃ deposits such as the White Cliffs of Dover ( http://www.nationaltrust.org.uk/main/w-vh/w-visits/w-findaplace/w-thewhitecliffsofdover/ ).

# Current funding from: “Collaborative Research: Regulation Of The C4-CO₂ Concentrating Mechanism In Marine Diatoms By CO₂, Light, And Nutrients”; J. Reinfelder, PI; K. Bidle and A. Milligan, Co-PIs; National Science Foundation, Ocean Sciences, Biological Oceanography; OCE-0526365.

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Last updated: 10/2007