Dimensions: Collaborative Research: Functional Diversity of Microbial Trophic Guilds Defined Using Stable Isotope Ratios of Proteins

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Advancements in DNA sequencing technology have accelerated the pace of discovery of species and gene distributions, especially for microorganisms. This acceleration contrasts with slower progress in linking environmental genetics and taxonomic diversity to the function, resource utilization, and ecological niches of these organisms. This project will develop a novel application of isotope geochemistry and apply it in the field of biochemical oceanography as a first step toward tackling these challenges. The goal of the project is to combine natural isotope ratio data with proteomics. Different metabolic processes yield different ratios of the stable isotopes of carbon, nitrogen, hydrogen, and sulfur; and by measuring these ratios on specific proteins, these natural isotope signals can attribute biogeochemical processes (functions) to specific microbes (taxonomic and genetic information). Because this is a novel methodology, the project first will seek to identify the fundamental principles of natural isotopic sorting that could result from different types of trophic structure. This will be implemented using pure cultures and then will be tested on a model ecosystem from a stratified lake. An example of a question to be answered is: How does the distribution of organisms' genetic fingerprints in a mixed microbial community scale with the community's genetic diversity? Does higher genetic diversity predict more trophic, or feeding, levels?This research will help to develop a concept of trophic guilds and ecosystem dependence for microbes; such concepts are well developed in macro-ecology, but remain less well understood for microbial diversity. Ecosystem conservation is not possible without a better understanding of what maintains microbial functional and genetic diversity. The success of this project could lead to many further applications for understanding the physiological and ecological roles of uncultured microbes in the environment. The project has three principal investigators: an isotope geochemist, a microbial physiologist, and a microbial ecologist - a team well suited to achieve the interdisciplinary goal of linking geochemistry with microbial diversity. The proposed activities will educate a post-doctoral investigator, two graduate students, and several undergraduate summer students. Through additional activities such as The Cambridge Science Festival and Science by the Pint, the research also will be communicated to the general public.