UNDERSTANDING THE CLIMATE RESPONSE CONSEQUENCES OF CHANGING ELEMENTAL USE EFFICIENCIES IN PROCHLOROCOCCUS

Anthropogenic climate change is rapidly reshaping the ecology and physiology of biogeochemically significant phytoplankton. While phytoplankton are consistently subjected to multiple interacting abiotic factors, most biogeochemical models are based on data from single-stressor experiments. Ubiquitously abundant between 40°N and 40°S, the photosynthetic cyanobacterium Prochlorococcus plays a vital role in global primary production and supports microbial food webs in oligotrophic regions. This study examines the physiology of high-light Prochlorococcus strains MIT1314 (Station ALOHA, North Pacific) and MED4 (Mediterranean Sea) in a climate-relevant context by growing them across their full thermal range under varying nutrient limitations (nitrogen, phosphorus, and iron). To quantify the synergistic effects of temperature and nutrient availability, we used elemental use efficiencies (EUEs), measuring carbon fixation rates normalized to the cell quota of the most limiting nutrient. Our results reveal strain-specific temperature-nutrient interactions, indicating that regional microdiversity contributes to physiological responses under future climate scenarios. Under warmer, iron-limited conditions, MED4 exhibited higher iron use efficiency (IUE), potentially reflecting greater metabolic efficiency—a response not observed in MIT1314. These findings, alongside other distinct physiological responses, provide mechanistic insights into how temperature-nutrient interactions may shape the functional diversity of this key group of primary producers. Anthropogenic climate change is rapidly reshaping the ecology and physiology of biogeochemically significant phytoplankton. While phytoplankton are consistently subjected to multiple interacting abiotic factors, most biogeochemical models are based on data from single-stressor experiments. Ubiquitously abundant between 40°N and 40°S, the photosynthetic cyanobacterium Prochlorococcus plays a vital role in global primary production and supports microbial food webs in oligotrophic regions. This study examines the physiology of high-light Prochlorococcus strains MIT1314 (Station ALOHA, North Pacific) and MED4 (Mediterranean Sea) in a climate-relevant context by growing them across their full thermal range under varying nutrient limitations (nitrogen, phosphorus, and iron). To quantify the synergistic effects of temperature and nutrient availability, we used elemental use efficiencies (EUEs), measuring carbon fixation rates normalized to the cell quota of the most limiting nutrient. Our results reveal strain-specific temperature-nutrient interactions, indicating that regional microdiversity contributes to physiological responses under future climate scenarios. Under warmer, iron-limited conditions, MED4 exhibited higher iron use efficiency (IUE), potentially reflecting greater metabolic efficiency—a response not observed in MIT1314. These findings, alongside other distinct physiological responses, provide mechanistic insights into how temperature-nutrient interactions may shape the functional diversity of this key group of primary producers.    

Presentation Preference: Oral

Primary Presenter: Bradley Mackett, University of Southern California (mackett@usc.edu)

Authors:

Bradley Mackett Mackett, University of Southern California  (mackett@usc.edu)

Yutong Chen, University of Southern California  (yutongc@usc.edu)

Feixue Fu, University of Southern California  (ffu@usc.edu)

David Hutchins, University of Southern California  (dahutch@usc.edu)