Trading Essentials: Investigating the Impact of Cofactor Exchange on Microbial Community Dynamics, Carbon Use Efficiency, and Soil Ecosystem Processes

Soil is teeming with bacteria and other microbes that drive the flow of nutrients on Earth, absorbing and releasing greenhouse gases like carbon dioxide (CO2). This nutrient flow depends on the ways different microbial species interact with each other and with other organisms including plants. As plant roots grow through soil, they release chemicals that feed the surrounding microbes in the region around roots known as the rhizosphere. In the rhizosphere, microbes also interact with each other by sharing micronutrients such as vitamins, but how micronutrient sharing impacts microbial community dynamics remains unknown. To study the links between microbial growth, micronutrient sharing, and carbon release, researchers will assemble a model community of bacteria within customized chambers that mimic the chemical environment of the rhizosphere. This novel experimental system will serve as a model for other scientists studying similar processes. Results of this study will be used to test existing computational models that predict how soil microbial communities influence carbon cycling. In addition to training students and postdoctoral scholars, this project will involve local 6th and 7th graders and their teachers to bring authentic research experiences to classrooms and to train the next generation of scientists. Microbial community assembly in the rhizosphere is shaped by microbial interactions, functional traits, and changing root chemistry. These factors modulate carbon use efficiency (CUE) – the proportion of carbon taken up by microbes and assimilated as biomass rather than released by respiration as CO2. Microbial CUE is key to forming stable soil organic matter. While it is known that macronutrient cycling (e.g. carbon, nitrogen, or phosphorus) contributes to microbial community assembly, the roles of micronutrient-sharing interactions are not well understood. This project will use corrinoids – vitamin B12 and related micronutrients – as a model to characterize the functional roles of micronutrient-sharing bacteria as well as their links to macronutrient cycling and important biogeochemical processes in the rhizosphere. Research activities include (1) prediction of how corrinoids influence the ecology of rhizosphere bacteria by assessing corrinoid-dependent interactions with bacteria grown individually and in combination with others; (2) development of a model rhizosphere bacterial community to study how corrinoids alter their ecology, the availability of macronutrients, and together how these interactions shape bacterial succession; and (3) construction of gene knockouts as well as community dropouts to examine how disruptions in micronutrient interactions impact bacterial community dynamics. Researchers will modify an existing dynamic energy budget model to incorporate micronutrient interactions in order to show how these interactions alter microbial community phenotypes, such as CUE. 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.