title: Interaction and signalling between a cosmopolitan phytoplankton and associated bacteria.
abstract: Interactions between primary producers and bacteria impact the physiology of both partners, alter the chemistry of their environment, and shape ecosystem diversity. In marine ecosystems, these interactions are difficult to study partly because the major photosynthetic organisms are microscopic, unicellular phytoplankton. Coastal phytoplankton communities are dominated by diatoms, which generate approximately 40% of marine primary production and form the base of many marine food webs. Diatoms co-occur with specific bacterial taxa, but the mechanisms of potential interactions are mostly unknown. Here we tease apart a bacterial consortium associated with a globally distributed diatom and find that a Sulfitobacter species promotes diatom cell division via secretion of the hormone indole-3-acetic acid, synthesized by the bacterium using both diatom-secreted and endogenous tryptophan. Indole-3-acetic acid and tryptophan serve as signalling molecules that are part of a complex exchange of nutrients, including diatom-excreted organosulfur molecules and bacterial-excreted ammonia. The potential prevalence of this mode of signalling in the oceans is corroborated by metabolite and metatranscriptome analyses that show widespread indole-3-acetic acid production by Sulfitobacter-related bacteria, particularly in coastal environments. Our study expands on the emerging recognition that marine microbial communities are part of tightly connected networks by providing evidence that these interactions are mediated through production and exchange of infochemicals.
authors.affiliation: 1] School of Oceanography, University of Washington, Seattle, Washington 98195, USA [2] Chemistry Faculty, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: S A
authors.initials: SA
authors.lastname: Amin
authors.affiliation: Department of Microbiology, University of Washington, Seattle, Washington 98195, USA.
authors.forename: L R
authors.initials: LR
authors.lastname: Hmelo
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: H M
authors.initials: HM
authors.lastname: van Tol
authors.affiliation: Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: B P
authors.initials: BP
authors.lastname: Durham
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: L T
authors.initials: LT
authors.lastname: Carlson
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: K R
authors.initials: KR
authors.lastname: Heal
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Morales
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: C T
authors.initials: CT
authors.lastname: Berthiaume
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Parker
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: B
authors.initials: B
authors.lastname: Djunaedi
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Ingalls
authors.affiliation: Department of Microbiology, University of Washington, Seattle, Washington 98195, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Parsek
authors.affiliation: Department of Marine Science, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Moran
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
authors.forename: E V
authors.initials: EV
authors.lastname: Armbrust
mesh_terms: D017377:Diatoms / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D017753:Ecosystem; D007210:Indoleacetic Acids / Q000378:metabolism*; D055432:Metabolomics; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D010788:Photosynthesis; D010839:Phytoplankton / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D041902:Rhodobacteraceae / Q000235:genetics / Q000378:metabolism*; D012623:Seawater / Q000737:chemistry; D059467:Transcriptome; D014364:Tryptophan / Q000378:metabolism
chemical_list: D007210:Indoleacetic Acids; C030737:indoleacetic acid; D014364:Tryptophan