Heithoff Abigail

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  • Preprint
    Phosphorus supply drives rapid turnover of membrane phospholipids in the diatom Thalassiosira pseudonana
    ( 2010-11) Martin, Patrick ; Van Mooy, Benjamin A. S. ; Heithoff, Abigail ; Dyhrman, Sonya T.
    In low phosphorus (P) marine systems phytoplankton replace membrane phospholipids with non-phosphorus lipids, but it is not known how rapidly this substitution occurs. Here, when cells of the model diatom Thalassiosira pseudonana were transferred from P-replete medium to P-free medium, the phospholipid content of the cells rapidly declined within 48 h from 45±0.9% to 21±4.5% of total membrane lipids; the difference was made up by non-phosphorus lipids. Conversely, when P-limited T. pseudonana were resupplied with P, cells reduced the percentage of their total membrane lipid contributed by a non-phosphorus lipid from 43±1.5% to 7.3±0.9% within 24 h, while the contribution by phospholipids rose from 2.2±0.1% to 44±3%. This dynamic phospholipid reservoir contained sufficient P to synthesize multiple haploid genomes, suggesting that phospholipid turnover could be an important P source for cells. Field observations of phytoplankton lipid content may thus reflect short-term changes in P supply and cellular physiology, rather than simply long-term adjustment to the environment.
  • Article
    The transcriptome and proteome of the diatom Thalassiosira pseudonana reveal a diverse phosphorus stress response
    (Public Library of Science, 2012-03-29) Dyhrman, Sonya T. ; Jenkins, Bethany D. ; Rynearson, Tatiana A. ; Saito, Mak A. ; Mercier, Melissa L. ; Alexander, Harriet ; Whitney, LeAnn P. ; Drzewianowski, Andrea ; Bulygin, Vladimir V. ; Bertrand, Erin M. ; Wu, Zhijin ; Benitez-Nelson, Claudia R. ; Heithoff, Abigail
    Phosphorus (P) is a critical driver of phytoplankton growth and ecosystem function in the ocean. Diatoms are an abundant class of marine phytoplankton that are responsible for significant amounts of primary production. With the control they exert on the oceanic carbon cycle, there have been a number of studies focused on how diatoms respond to limiting macro and micronutrients such as iron and nitrogen. However, diatom physiological responses to P deficiency are poorly understood. Here, we couple deep sequencing of transcript tags and quantitative proteomics to analyze the diatom Thalassiosira pseudonana grown under P-replete and P-deficient conditions. A total of 318 transcripts were differentially regulated with a false discovery rate of <0.05, and a total of 136 proteins were differentially abundant (p<0.05). Significant changes in the abundance of transcripts and proteins were observed and coordinated for multiple biochemical pathways, including glycolysis and translation. Patterns in transcript and protein abundance were also linked to physiological changes in cellular P distributions, and enzyme activities. These data demonstrate that diatom P deficiency results in changes in cellular P allocation through polyphosphate production, increased P transport, a switch to utilization of dissolved organic P through increased production of metalloenzymes, and a remodeling of the cell surface through production of sulfolipids. Together, these findings reveal that T. pseudonana has evolved a sophisticated response to P deficiency involving multiple biochemical strategies that are likely critical to its ability to respond to variations in environmental P availability.
  • Thesis
    N2 fixation by subsurface populations of Trichodesmium : an important source of new nitrogen to the North Atlantic Ocean
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2011-02) Heithoff, Abigail
    Trichodesmium, a genus of diazotrophic cyanobacteria, is an important contributor to the marine nitrogen (N) and carbon (C) cycles. The extent to which Trichodesmium dinitrogen (N2) fixation contributes to the marine N cycle has been modeled based on abundance data and rate estimates from surface populations. However, recent data show that Trichodesmium populations have a broad vertical distribution. The presence of previously unaccounted for subsurface populations suggests that past estimates of the contribution of new N by Trichodesmium to the North Atlantic may be artificially low. Herein, culture and field studies were combined to examine trends in N2 fixation in discrete surface and subsurface Trichodesmium populations in the western North Atlantic. Surface populations were dominated by the raft colony morphology of Trichodesmium and surface N2 fixation rates ranged from (33 to 156 μmol h-1 mol C-1). Subsurface populations were dominated by the puff colony morphology. Subsurface N2 fixation was typically detectable, but consistently lower than surface population rates (9 to 88 μmol h-1 mol C-1). In an analysis of the entire field dataset, N2 fixation rates varied non-linearly as a function of in situ irradiance. This trend in N2 fixation versus in situ irradiance is consistent with field and culture observations in the literature (Bell et al., 2005; Capone et al., 2005), however other models that predict N2 fixation based on light predict higher subsurface N2 fixation than what was detected in this study. In culture, N2 fixation in Trichodesmium was proportional to light level over the range of irradiances tested (10 to 70 μmol quanta m-2 s-1) and over long and short time scales, suggesting subtle changes in the light field could depress subsurface N2 fixation. Since the subsurface samples were dominated by the puff colony morphology, it is unclear if the subsurface N2 fixation rates are the result of the intrinsic responses of different species of Trichodesmium, or light driven population segregation within a single species, among other possibilities including the effects of temperature and nutrient availability. Regardless, the subsurface rates presented herein indicate that N2 fixation by subsurface populations represents an undersampled source of new N to the western north Atlantic. This result is consistent with the findings of Davis and McGillicuddy (2006), who suggest that subsurface populations of Trichodesmium increase the average N2 fixation rate in the North Atlantic by 2.9 to 3.3 times over estimates based solely on surface estimates (Davis and McGillicuddy, 2006).