Bacteria that assemble in phycospheres that surround living phytoplankton cells process a substantial proportion of ocean primary productivity, yet the identity of the metabolites driving these micron-scale carbon-cycle hotspots are poorly known. Using transposon mutant libraries of copiotrophic marine bacterium <em>Ruegeria pomeroyi</em> DSS-3, we are learning new details about its metabolite-based interactions with phytoplankton hosts and with other bacterial species sharing the phycosphere. In one example, a set of <em>R. pomeroyi</em> transporter mutants were screened for growth on metabolites known to be produced by phytoplankton but without a known bacterial transporter. This resulted in new or confirmed annotations of cognate substrates for 17 transporters. In a second example, differential growth rates of mutants inoculated as a pooled library into model phycospheres revealed specific genes necessary for <em>R. pomeroyi</em> success when interacting with other phycosphere bacteria. We learned that the bacterium relied more on uncontested substrates, competed for nitrogen in the forms of ammonium and amino acids, and obtained nucleosides via cross-feeding. Mutant libraries of ecologically-relevant bacteria can be powerful tools for generating and testing hypothesis, and for accelerating gene annotation.

Primary Presenter: Mary Ann Moran, University of Georgia (mmoran@uga.edu)

Authors:

Mary Ann Moran, University of Georgia  (mmoran@uga.edu)

Jeremy Schreier, Universiy of Georgia  (jeremy.schreier@uga.edu)

William Schroer, University of Georgia  (william.schroer@uga.edu)