Collaborative Research: RUI: Implications of bacterially driven cross-kingdom chemical interactions

Over evolutionary history, microbes have evolved in close association with larger, more complex organisms, often driven by the mutually beneficial exchange of nutrients. Advancements in analytical techniques have revealed that many host-bacterial interactions are tightly regulated by small molecules, acting as chemical messengers. Yet, connecting how these interactions at the cellular level translate to impacts on whole communities and ecosystems remains an ongoing challenge necessitating cross-disciplinary collaboration.

A newly emerging picture suggests that marine bacteria are not passive in their interactions with hosts such as algae; rather bacteria actively mediate the flow of organic matter depending on how they deploy their chemical arsenal. The assembled interdisciplinary team will develop new methods to track and translate complex chemical signals between a model algal host and associated bacteria.

New methodologies in fluorescent biosensors will quantify bacterial production of chemical signals at the cellular level, whose release manipulates host physiology. How the host responds to the chemicals will be assessed by measuring changes in the host's proteins, RNA, and metabolites. This work supports the training and mentoring of underrepresented/underresourced postdoctoral and undergraduate trainees in themes bridging the chemical, biological, and environmental sciences.

Four postdoctoral investigators will participate in course-based undergraduate research experiences with Haverford faculty with the goal of building supportive scholar-teacher mentoring networks with students and providing training in equitable and inclusive course design so that the scholars becoming more reflective, engaged, and effective teachers. All four PIs will develop conference-based experiential workshops to provide career development.

Microbes have emerged as key players in marine systems where they form complex relationships with eukaryotic phytoplankton. These interactions range from symbiotic to pathogenic and are tightly regulated through the dynamic exchange of small molecule chemical messengers that shape communities and influence the biogeochemical fate of oceanic nutrients.

Efforts to elucidate the exchange of chemical signals and decipher the environmental drivers of bacterial-phytoplankton interactions are limited and met with substantial technical challenges. Recently, two chemical messengers, tetrabromopyrrole (TBP) and 2-heptyl-4-quinolone (HHQ), both produced by the globally distributed marine gamma proteobacterium, Pseudoalteromonas, have been identified to govern the physiology of its associated, bloom-forming single-cell algal host, Emiliania huxleyi, with contrasting modalities.

Experiments outlined in this study are poised to tease apart the metabolic landscape defining this model host-bacterial symbiosis, and detail when and how chemical messengers induce host metabolic reprogramming resulting in ecosystem level consequences. Three synergistic aims will be accomplished: in the first, TBP and HHQ production and uptake will be measured in response to nutrient variability and HHQ production will be captured at the single-cell level using biosensors.

In the second aim, experiments will reveal metabolic cross-talk by establishing the metabolomic and proteomic response of E. huxleyi to both P. piscicida and HHQ, while tracking P. piscicida uptake of E. huxleyi-derived metabolites. In the third, experiments will investigate if HHQ prevents E. huxleyi viral entry using electron microscopy, accounting for an earlier observation that viral-induced mortality of E. huxleyi is stalled in the presence of HHQ.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.