title: Abundances of iron-binding photosynthetic and nitrogen-fixing proteins of Trichodesmium both in culture and in situ from the North Atlantic.
abstract: Marine cyanobacteria of the genus Trichodesmium occur throughout the oligotrophic tropical and subtropical oceans, where they can dominate the diazotrophic community in regions with high inputs of the trace metal iron (Fe). Iron is necessary for the functionality of enzymes involved in the processes of both photosynthesis and nitrogen fixation. We combined laboratory and field-based quantifications of the absolute concentrations of key enzymes involved in both photosynthesis and nitrogen fixation to determine how Trichodesmium allocates resources to these processes. We determined that protein level responses of Trichodesmium to iron-starvation involve down-regulation of the nitrogen fixation apparatus. In contrast, the photosynthetic apparatus is largely maintained, although re-arrangements do occur, including accumulation of the iron-stress-induced chlorophyll-binding protein IsiA. Data from natural populations of Trichodesmium spp. collected in the North Atlantic demonstrated a protein profile similar to iron-starved Trichodesmium in culture, suggestive of acclimation towards a minimal iron requirement even within an oceanic region receiving a high iron-flux. Estimates of cellular metabolic iron requirements are consistent with the availability of this trace metal playing a major role in restricting the biomass and activity of Trichodesmium throughout much of the subtropical ocean.
authors.affiliation: Ocean and Earth Science, National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, United Kingdom. s.richier@noc.soton.ac.uk
authors.forename: Sophie
authors.initials: S
authors.lastname: Richier
authors.forename: Anna I
authors.initials: AI
authors.lastname: Macey
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Pratt
authors.forename: David J
authors.initials: DJ
authors.lastname: Honey
authors.forename: C Mark
authors.initials: CM
authors.lastname: Moore
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Bibby
mesh_terms: D000064:Acclimatization / Q000187:drug effects; D001267:Atlantic Ocean; D001426:Bacterial Proteins / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005843:Geography; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D033862:Iron-Binding Proteins / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000187:drug effects; D010088:Oxidoreductases / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D033862:Iron-Binding Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; C089909:photosystem I, psaB subunit; C422369:photosystem II, psbA subunit; D002734:Chlorophyll; D007501:Iron; D010088:Oxidoreductases; C029130:nitrogenase reductase