In this research project, the investigator will study bacterial foraging in the marine environment by developing a state-of-the-art experimental technique integrating digital holographic microscopy and microfluidics, to obtain three dimensional trajectories of marine bacteria. This sophisticated technique will provide unprecedented access to (i) high-resolution information on bacterial swimming in 3D; and (ii) the ability to micromanipulate nutrient landscapes and quantify the resulting bacterial response. By combining observations with novel mathematical models based on a cost benefit approach to bacterial foraging, this research will:
1. provide the first quantitative description of the swimming strategies of marine Bacteria 2. quantify the foraging performance of motile marine bacteria 3. predict under what conditions and to what extent foraging of swimming bacteria affects turnover rates of dissolved organic matter in the ocean.
The new technique to be pioneered as part of a CAREER award will have broad impact well beyond the proposed research, by breaking the traditional sizebarrier limiting ecological investigations at the microscale: the ability to systematically control a microorganism's environment using microfluidics, while capturing its detailed, 3D response with holography, unlocks access to a broad range of fundamental microbial processes. Their quantitative understanding is pivotal for our ability to correctly predict the future state of the oceans. At the same time, awareness of the importance of these microscale processes and the complexity of the marine ecosystem is a critical factor in educating the next generation of scientists and citizens to the delicate balance of the oceans and how human activities as well as global change hinge on it. This CAREER award will significantly contribute to this goal, by supporting a broad educational plan. Funding will support the interdisciplinary education of two Ph. D. students, international teaching and recruitment of minority students. The background and highlights of the proposed research will be shared with the public in talks and interviews by leveraging partnerships with important dissemination channels like Boston's Museum of Science. The core of the outreach program will be targeted at middle-school children, in the form of an original, educational video game (Virtual Microbe) that teachers will find freely available for use to integrate in their curricula and widely disseminated on high-impact, teacher-dedicated web portals of public television stations, including Maryland Public Television and WGBH.
The productivity and health of the Oceans are governed by a suite of organisms and biological processes that live at the microscale. Only the ability to interrogate and quantify these microbial interactions and dynamics can allows us to obtain better predictive power about the future state of the Oceans, yet such microscale investigations have been few and limited by technological hurdles. In this CAREER award we have developed and applied a new set of tools to study the Oceans’ microscale: microfluidics. By using microfluidic devices to accurately control the chemical and physical microenvironment of cells – for example nutrient conditions and flow – and by simultaneously imaging the cells’ response at unprecedented spatial and temporal resolution, we popped open the black box of microbial interactions in the sea and uncovered a range of previously unknown biophysical mechanisms that shape the life of marine plankton. The direct visualization of microbes, and in particular of their motility under different environmental conditions, has proven to be a particularly powerful approach for rigorous hypothesis testing, especially in conjunction with mathematical modeling. As a result of this work, we now have a much better appreciation for some of the striking adaptations and dynamics of plankton, their implications in oceans’ biogeochemical cycles, their interaction with turbulence and ocean currents, and their chemical signaling abilities. Moreover, we have established a palette of microscale tools that can aid oceanographers and microbial ecologists to decipher the interactions among the smallest life forms on earth, in marine and aquatic environments, and beyond. This award has resulted in 37 scientific publications, with more than half of them in high-impact, interdisciplinary journals. This has attracted attention to marine microbial processes by a broad range of scientists, in particular physicists, and has contributed to disseminate the richness of marine microbial dynamics. Over 20 young scientists, between graduate and postgraduate students, have been involved in this work over five years, contributing to train the next generation of biophysicists and microbial oceanographers in quantitative, interdisciplinary, cutting edge experimental methods. Here only three illustrative highlights from this body of work are given. First, we have discovered a new mechanism by which phytoplankton can accumulate in dense aggregations known as ‘thin layers’, which resemble to and sometimes act as precursors of red tides. We found that, when phytoplankton cells migrate through the water column in search of light, their motion can be halted by ocean currents, which limit the directionality of their swimming and trap them at depth, forming intense thin layers. Second, we have found that the chemical sensing and the motile response of marine microbes can play a significant role in the ocean’s sulfur cycle, which in turn is implicated in regional climate dynamics, by mediating which sulfur transformation pathway is favored. Here, the ability to set up precise chemical gradients and directly image motile protists allowed us to overturn the previous paradigm of a broadly important sulfur compound (DMSP) acting as a protist grazing deterrent by the phytoplankton that produce it. Third, we have identified a new trick up the sleeve of marine microbes, which may interest up to 95% of motile marine bacteria. We found that, in order to turn (change direction), these bacteria exploit a buckling instability in their flagellum, which effectively allows them to reorient without the need of a dedicated steering mechanism and providing one of the first connections between microbiology and mechanics. Taken together, these findings highlight that the ocean has many more surprises in store when it comes to the fundamental processes that govern its microscale dynamics. As part of this CAREER award, we have also worked at conveying this to a broad audience of young students, through the development of an educational video game. This game, ‘Ocean NanoBots’, puts the student in the driver seat: by ‘engineering’ analogues of microbes, controlling their functions and behavior, and letting them act and interact in virtual ocean scenarios, the game allows students to understand the vital dynamics that microbes play for the status of our Oceans’ health.
