Microbiology: Exclusive networks in the sea.

Abstract

The identification of an exchange of nutrients and signalling molecules between a planktonic alga and a bacterium demonstrates that targeted mutualistic interactions occur across domains of life in the oceans. See Letter p.98 Experimental difficulties mean that little is known about the interplay between phytoplankton and bacteria that provides the foundation of marine ecosystems. Here Virginia Armbrust and colleagues use a laboratory model system to characterize a bacterial consortium associated with a globally distributed diatom. They find that in consortium culture experiments Sulfitobacter sp. promote cell division in the diatom Pseudo-nitzschia multiseries through secretion of the indole-3-acetic acid (IAA), which is synthesized from both diatom-secreted and endogenous tryptophan. The authors use metabolomics and metatranscriptomics to identify IAA and some of the genes associated with IAA production in the ocean, although further work will be needed to fully investigate the ecological relevance of the pathway identified in the laboratory. This study is among the first to characterize at the molecular level the currency used to support a microbial consortium in the ocean and lays the groundwork for future efforts.