Project: Direct measurement of in situ growth and growth limitation of bacterioplankton species

NSF Award Abstract:
Marine microbes, including bacteria and archaea, account for up to 70% of biomass in the ocean. How this biomass turns over has large implications for the global cycling of carbon and many other elements. Recent efforts have shown that a microbial community at a certain location and time is composed of metabolically diverse, co-existing species and that the most abundant microbes do not necessarily display the highest metabolic activity. However, we still lack an understanding of fundamental ecological parameters including how different bacteria and archaea contribute to global element cycles, how their mass and growth rates are distributed across the diverse species and how these parameters change under varying conditions. This project uses a novel technology that enables precise measurement of single cell mass and growth rate in natural samples. The goal is to characterize how mass and growth of diverse species respond to environmental changes in the ocean and determine how this response is translated into cycling of global carbon and other elements. The results fill a knowledge gap on how environmental changes govern microbial populations and the consequential broader processes related to global climate and human interactions with the ocean. In addition to advancing the scientific understanding, this work contributes to the academic training of students and postdoctoral scholars in a highly interdisciplinary manner and will also produce podcasts describing the work and its progress to a broader audience.

Central to this project is a technology called Suspended Microchannel Resonator, a well-proven microfluidics-based mass-sensor that precisely measures mass and growth rate of individual cells. Importantly, growth is directly measured as the addition of biomass and thus reflects the instantaneous growth of a microbe at the time the seawater sample was collected. This technology is being applied to characterize mass and growth of diverse species in a series of natural samples from coastal environments and complemented with gene sequencing and elemental analysis to estimate the contributions to element cycles. The project addresses the following questions: (i) How fast do different bacterial species grow in their native seawater over different timescales and how is growth related to relative abundance from sequencing data? (ii) What is the contribution of individual species to carbon, nitrogen, and phosphorous turnover? (iii) What nutrients limit bacterial growth under given conditions? (iv) Can in situ growth rates of populations be inferred from their single cell mass distributions?