Photosynthetic microbes in surface ocean waters carry out nearly half of global net primary production, both supporting the marine food web and reducing atmospheric carbon dioxide. The fate of carbon in ocean ecosystems is controlled by myriad individual interactions within a highly interconnected planktonic food web. The role of marine viruses has proven difficult to quantify, in part due to poor understanding of the ecological and biogeochemical role of intact, virus-infected microbes. During infection, viruses alter host cellular metabolism and chemical cues released from intact, virus-infected cells likely attract neighboring plankton via chemotaxis. Virus-induced dissolved organic carbon release likely alters both marine microbial community composition and micron-scale spatial structure, increasing organism encounter rates, and subsequently, carbon flux across trophic levels. The goal of the proposed work was to develop a mechanistic understanding of the role of intact, virus-infected cells in oceanic carbon cycling to inform our view of viral impacts on ocean ecosystem function.

Through a highly collaborative effort blending tools from microbial ecology, microfluidics, and metabolomics, the chemotactic responses of bacteria toward exudates from virus-infected cells and an array of identified metabolites and compounds were directly quantified, providing new key evidence for the mechanisms regulating carbon flux across trophic levels. Specifically, exudates from virus-infected cells (Synecchococcus) at different stages of the infection cycle were assayed using microfluidics to determine the degree to which they act as chemoattractants for model bacteria (Vibrio alginolyticus). These studies reveal significant chemoattraction to pre-lysis exudates. This work also motivated the development of new, high-throughput lab-on-a-chip microfluidic devices to vastly accelerate the pace of discovery for chemical ecology and other relevant applications. A multiplexed microfluidic device was successfully designed, fabricated, and tested, which automatically performs multiple chemotaxis assays in parallel across a range of predefined chemostimulus concentrations. The research themes examined under this award were extended to study the mechanisms regulating cell and chemical transport, and thus encounter rates, in physically relevant systems. New mathematical approaches were applied to quantify the collective motility of dense suspensions of swimming bacteria and how this motion contributes to the dispersal of chemical signals and nutrients. Furthermore, swimming cells are live in porous marine sediments and marine snow particles. Microfluidic model porous media were used to quantify the effects of porous microstructure and external cues on the navigation of swimming bacteria in such environments.

This work supported the education and training of seven individuals, including: two postdoctoral associates, two graduate students, two undergraduate students, and one high school student. Through this award, a one-day workshop was co-organized at the ASLO Ocean Sciences Meeting 2022 entitled “Advancing microfluidics and metabolomics in microbial ecology” in a virtual format on February 24, 2022. The workshop brought together leaders in the respective fields of microfluidics, metabolomics, and viral ecology along with postdoctoral researchers and undergraduate and graduate students to discuss the engineering, chemical, and ecological aspects at the intersection of these disciplines. The workshop was highlighted by three keynote talks.

Last Modified: 01/01/2023
Modified by: Jeffrey Guasto