Marine ecosystems are primarily microbial in nature. Microscopic organisms represent over 90% of biomass, including the major primary producers, and drive biogeochemical processes. Although this insight is merely 30 years old, it has led to concerted efforts in studying the structure and functioning of microbial communities in the ocean. Techniques are now available to estimate many key ecological parameters of microbial life; however, one fundamental gap is that estimates of microbial growth rates in the wild remain poorly constrained. Questions, which have largely remained unsolved, are:
What does the growth rate distribution look like for free-living microbes? Which species grow at what rates? How do environmental changes (e.g., nutrients, light) affect growth rates of different microbes?
To begin to address these questions, this project will develop a single-cell based system that allows coupled measurement of in situ growth rates and genomic characteristics. The suspended microchannel resonator (SMR) is a well-developed microfluidics-based mass-sensor that has sufficient resolution for measuring the natural range in size and growth rate of ocean microbes; here, this system will be adapted to enable: (i) capture and growth measurement of individual microbial cells in their native seawater microenvironment, (ii) genomic analysis of the same cells for which growth rates have been determined, and (iii) direct analysis of bacterioplankton communities obtained from mesocosm and natural ocean samples. This system is unique in that it couples quantitative growth rate determination and genomic identification of individual microbial cells in their natural microenvironment, and therefore promises to be applicable to the above questions.
Intellectual Merit: Understanding what regulates bacterial growth on the single cell and population level is of fundamental importance in linking microbial diversity to function, and to model and predict carbon fluxes in the ocean. This project establishes a prototype system to couple determination of growth and genomics on the single cell level, for which no data currently exist. Future directions will include design of a system with increased throughput and capability of running onboard ship or autonomous sampling devices.
Broader Impacts: Broader impacts arise from graduate and undergraduate student training, and communication with the scientific community and the public. Students will be trained in an interdisciplinary manner in a project that unites aspects of engineering and science. Thesis committees will reflect this diversity of fields. Building plans for the system will be made available over the web. The project will also engage in a public outreach program, for which undergraduates will produce a series of podcasts. Emphasis will be given to describing the process of doing engineering and science rather than only results. Podcasts will be made available on the project's website and Facebook page, and also through the website of MIT's Earth System Initiative and the MIT portal on iTunes. Listeners will be invited to subscribe, and will be given the option of providing contact information. The effectiveness of the podcasts will be assessed through surveys of these confirmed listeners. In addition, podcasts will be played for participants in MIT's teen outreach programs, and their effectiveness with these teen audiences will be assessed.