Award: IOS-2041497

Our project set out to decode the chemical conversations shared by microscopic life in the oceans phycospherethe thin halo of seawater surrounding individual algal cells. We discovered that when the bloom-forming alga Emiliania huxleyi grows alongside the marine bacterium Pseudoalteromonas (A757), both partners keep dividing yet both undergo dramatic internal changes that rewire each others metabolism. Gene-expression, protein, and metabolite profiles revealed a hidden tug-of-war in which entire metabolic pathways surge or shut down, much like the physiological swings people feel during a cold or an allergy attack. One bacterial chemical message produced by A757, called 2-heptyl-4-quinolone (HHQ), proved especially powerful: delivered early, our work demonstrated that it could derail virus-algae infection dynamics, but late delivery offered no rescue. Additionally, we observed that algal nutrient stress appeared to ease the static growth of the alga induced by HHQ exposure, suggesting an interesting interplay between nutrient stress and cell-cell interactions. We developed a new method that makes it possible to detect bacterial proteins even when bacteria are present in extremely small amounts alongside much larger phytoplankton populations. By improving how data are collected and analyzed, we can now identify subtle changes in bacterial activity that were previously hidden. This approach is already helping collaborators study how bacterial processes influence the production of important bioactive compounds. Finally, using a fluorescent biosensor that glows when HHQ is made or sensed, we showed that A757 increases HHQ production in the presence of E. huxleyi and that muting a single quorum-sensing regulator flips the microbe from cooperative neighbor to virulent pathogen, attracting a swarm of bacteria to the algal surface. Ultimately, our better resolution of these fine-scale cell-cell interactions will enhance our understanding of the marine biogeochemical cycles and ocean ecosystem function. This NSF RUI grant supported the training of three postdoctoral investigators in course-based research experiences (CUREs) they brought to the classroom to engage in pedagogy training associated with the project. Over 15 Haverford undergraduate students participated directly in research aims associated with this grant with exchange between Haverford College and Georgia Institute of Technology. Additionally, this grant supported a graduate student at Georgia Tech who was subsequently awarded the NSF GRFP fellowship, and a technician at the University of Washington. PIs on this award co-organized a workshop at the Society of Integrative and Comparative Biology meeting entitled Balancing Act: A discussion on navigating diverse academic careers with dependents strategies, tips, and systemic change held in January 2024 in Seattle, WA. The workshop focused on addressing systemic issues related to balancing dependent care responsibilities with career advancement in academia, particularly for early career researchers. The workshop engaged 50 early career researchers/scientists/students in discussions offering practical recommendations and advocacy techniques to secure institutional support and promote a healthier work-life balance. This workshop offered early career scientists networking opportunities in a smaller workshop-style setting to engage in meaningful conversation around career support and advancement. Milestones & Key Findings Built and validated a fluorescent HHQ biosensor in Pseudoalteromonas A757. Charted 100 metabolic pathways disrupted during algalbacterial co-culture. Measured the impact of nutrient stress on the production of HHQ in A757. Demonstrated timing-dependent protection of E. huxleyi from viral lysis by HHQ. Showed nutrient stress modulatesbut does not haltHHQs influence on host physiology. Observed direct bacterial cling to algal surfaces correlating with algal decline. Tested CRISPR and alternative genome-editing routes to create stable sensor strains. Deposited open-access multi-omics datasets and protocols supporting community reuse. Last Modified: 08/26/2025 Submitted by: BrookLNunn