DISTINCT PHYSIOLOGICAL RESPONSES OF SOUTHERN OCEAN MIXOTROPHS TO IRON AND MANGANESE LIMITATION

In the Southern Ocean (SO), the physiological mechanisms mixotrophs use to cope with iron (Fe) or manganese (Mn) deficiency are not well understood, limiting predictions of carbon cycling seasonally. Laboratory cultures of two mixotrophic prasinophytes (Pyramimonas tychotreta and Mantoniella antarctica) and a cryptophyte (Geminigera cryophilia) from the SO are being examined to determine how Fe and Mn limitation affect behavior, growth, and metabolism. Growing under identical laboratory treatments, all cultures exhibited Fe limitation as indicated by reductions in growth rates, photosynthetic efficiency, and diameter compared to nutrient replete conditions. Of the three cultures, P. tychotreta showed the greatest sensitivity to metal limitation, sustaining 30% and 75% of its maximum growth rate under low Fe and low Mn conditions, respectively. G. cryophilia was also impacted by single Mn limitation, crashing after 4-6 transfers with cells displaying altered morphology not observed under Fe and Mn co-limitation. In contrast, the smallest organism M. antarctic demonstrated a 50% reduction in growth under Fe limitation, with Mn stress only evident through a reduction in diameter. This data suggests small SO mixotrophs may better tolerate Fe and Mn limitation, and that physiology under trace metal scarcity varies even among mixotrophs of the same phylogenetic group. Efforts are ongoing to integrate these results with grazing and transcriptomic data to further aid in our understanding of carbon flow in the SO. 

Presentation Preference: Oral

Primary Presenter: Claire Zwiers Cook, Skidaway Institute of Oceanography, University of Georgia (ccz99536@uga.edu)

Authors:

Claire Zwiers Cook, Department of Marine Sciences, Skidaway Institute of Oceanography, University of Georgia  (ccz99536@uga.edu)

Nicole Millette, Virginia Institute of Marine Science, College of William & Mary  (nmillette@vims.edu)

Natalie Cohen, Department of Marine Sciences, Skidaway Institute of Oceanography, University of Georgia  (cohen@uga.edu)