Project: Coordination of respiratory gene transcription and respiration in cultivated marine bacteria

Heterotrophic bacteria account for about half of the respiration in the oceans and they are the main consumers of dissolved organic materials, converting approximately 80% of assimilated organic carbon to carbon dioxide. Detailed examinations of the structure of microbial communities reveal that a highly diverse community of microorganisms must be responsible for the conversion of organic materials in the oceans. Recent studies suggest that most of growth-related activity is associated with a rather small number of abundant bacteria in the oceans. It is unclear, however, if the same observation applies to respiration, the dominant fate of organic carbon in the oceans. We currently lack tools for assessing respiration by specific microbes and for linking specific taxa with their contribution to carbon conversion and to carbon cycling.

The aim of this project is to develop a tool for understanding the contribution of bacterial groups to bacterial respiration. The proposed work will determine the relationship between transcription levels of oxidative phosphorylation genes and respiration rates in cultivated marine bacteria. The culture-based work is a necessary prerequisite to develop a metatranscriptomic tool for addressing ecological questions about the role of bacterial diversity in ocean carbon cycling. The project will include chemostat and batch culture studies with pure cultures and an incubation experiment with a naturally community of estuarine bacteria. Laboratory experiments will examine important heterotrophic bacteria in the oceans such as Pelagibacter ubique of the SAR11 clade and Ruegeria pomeroyi of the Roseobacter clade. Existing genome sequences will be analyzed to address the phylogenetic resolving power of respiration genes. The overarching goal of this proposal is to determine the relationship between abundances of respiration gene transcripts and respiration rates for bacterial taxa defined at different phylogenetic distances.