STRAIN-SPECIFIC EFFECTS ON GEPHYROCAPSA HUXLEYI BACTERIAL COMMUNITIES UNDER TEMPERATURE AND NITROGEN CO-STRESS

Environmental factors of climate change alter the interactions between bacteria and their algal hosts, known as the phycosphere, with broader implications for marine microbial community ecology. We examined the interactive effects of warming and nitrogen limitation on Gephyrocapsa huxleyi, a widely abundant and physiologically flexible coccolithophore, and its phycosphere. We subjected xenic cultures of G. huxleyi (strains RCC874 and RCC914) to N-replete and N-limited conditions at 3 temperature regimes: thermal optimum, moderate heat stress, and high heat stress. N limitation primarily drove cellular C:N:P ratios, while inter-strain differences in C:P ratio emerged with warming conditions. The main determinant of bacterial community composition was algal strain; temperature was also significant, but N had minimal impact. We identified strain-specific bacterial taxa in RCC914 (n=187) and RCC874 (n=303), indicating that unique physiological traits (e.g. variations in organic molecule production) support different bacterial communities. We measured osmolyte concentrations, which regulate osmotic pressure and cellular homeostasis. Notably, ectoine, an osmolyte not known to be synthesized by G. huxleyi, varied significantly between strains and N concentrations, suggesting bacterial modulation. Overall, our findings highlight how N limitation and warming interact to impact G. huxleyi physiology and phycosphere interactions at the strain level, emphasizing the importance of inter-strain differences in understanding marine ecosystems under changing climate conditions.

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Primary Presenter: Miah Manning, MIT-WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering (miahm@mit.edu)

Authors:

Miah Manning, MIT-WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering  (miah.manning@whoi.edu)

Arianna Krinos, Woods Hole Oceanographic Institution  (akrinos@whoi.edu)

Sara Shapiro, Woods Hole Oceanographic Institution  (sara.shapiro@whoi.edu)

Rayna Hamilton, Woods Hole Oceanographic Institution  (rayna.hamilton@whoi.edu)

Margaret Mars Brisbin, University of South Florida  (mmarsbrisbin@usf.edu)

Winifred Johnson, University of North Carolina Wilmington  (johnsonwm@uncw.edu)

Harriet Alexander, Woods Hole Oceanographic Institution  (halexander@whoi.edu)