EAGER: Cyanobacteria-Bacteria Associations in the Ocean and Their Biogeochemical Consequences

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Azam EAGER 1036613 Intellectual Merit: Pelagic marine bacteria and Archaea ("bacteria") play major roles in the variability in the biogeochemical fate of carbon fixed by phytoplankton in the ocean. The coupling of bacteria with the primary producers therefore has implications for climate and ecosystem models. Since bacteria interact with organic matter, including phytoplankton cells, at the nanometer to micrometer scale, understanding the biogeochemical coupling of bacteria with primary producers requires knowledge of the nature and strength of interactions at the micrometer scale. Using Atomic Force Microscopy (AFM) the PI recently discovered that a substantial fraction of heterotrophic (non-photosynthetic) bacteria, including the natural assemblages of Synechococcus, previously considered free-living, appeared conjoint with other bacteria. In a preliminary experiment, pelagic bacteria also became associated with cultures of Prochlorococcus (we do not yet know whether natural assemblages of Prochlorococcus harbor conjoint bacteria). In view of the biogeochemical importance of Synechococcus and Prochlorococcus as major primary producers in the ocean, their symbioses with heterotrophic bacteria could have far-reaching consequences. This EAGER study has the potential to change ideas on microbial carbon cycling and marine ecosystems functioning. It may reveal a novel microspatial context, e.g., carbon and nutrient cycling 'hot spots', particularly in oligotrophic waters where Synechococcus and Prochlorococcus are major primary producers. This potentially transformative, but high risk research, is an excellent fit to the EAGER model for funding. Cutting edge methodologies, including cryo-electron tomography, nanoSIMS and single cell phylogenetics will be used through multidisciplinary collaborations to test hypotheses on the ultrastructure and ecosystem function of the symbioses. The phylogenetic identity of the conjoint partners will be determined by direct micromanipulation of seawater samples to pick individual conjoint cells followed by analysis by MDA (Multiple Displacement Amplification). NanoSIMS analysis of intercellular elemental exchanges will characterize the nature and biogeochemical significance of the symbioses. Field studies will examine the distribution of the symbioses in relation to relevant environmental factors. Success in the goals detailed by the PI should yield mechanistic understanding and biogeochemical significance of the symbioses. We will rapidly communicate our findings in a wide circulation journal as well as through talks at appropriate conferences. Broader Impacts: This research project is aimed at gaining insights on fundamental mechanisms underlying the roles of microbes in the functioning of marine ecosystems, biological carbon cycling and the ocean's role in global climate variability. Therefore, the result should also be relevant to pressing societal issues fisheries and climate change. The PI's lab is actively involved in public education from local to international levels, and the findings of the proposed research will be disseminated broadly to the public in appropriately accessible formats. One postdoctoral fellow and one graduate student will receive training during this research.