Symbiosis Form an Inorganic Ferric Hydrolysis Species (Termed Fe Iii′), Which Can Be Assimilated by Algae

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symbiosis form an inorganic ferric hydrolysis species (termed Fe iii′), which can be assimilated by algae. A partnership cast in iron The authors confirmed that the VF–Fe iii complexes of Marinobacter spp. were sensitive to light, with photolysis rates that were 10–20-fold higher than those for other siderophores. Using radiola- belled VF–55Fe iii complexes, they found that, following photolysis of VF–Fe iii in attenuated sunlight, assimilation of iron by the phytoplankton-associated Marinobacter spp. increased by 70% and, importantly, this also led to a 20-fold increase in iron assimilation in the dinoflagellate Scrippsiella trochoidea. Although such an arrangement might be expected to be disadvantageous to the Marinobacter spp., Amin et al. observed that the growth of Marinobacter spp. in binary culture with S. trochoidea was dependent Many species of bloom-forming While investigating the marine on algal growth — no growth was algae in the phytoplankton form bacteria that are associated with observed for bacteria incubated beneficial or obligate associations with dinoflagellate and coccolitho- in algal culture media as a mono- marine bacteria. Such partnerships phore phytoplankton, Amin et al. culture — suggesting that growth are thought to enable the sharing of observed that members of the genus of Marinobacter spp. depends on metabolites and nutrients, although Marinobacter were present in over organic matter that is produced by a detailed understanding of most 80% of cultures. Interestingly, the phytoplankton. of these interactions is lacking. The only siderophore that the authors These data suggest that a acquisition of iron may be a key ele- were able to detect in the mutual- mutualistic partnership based on ment that drives such associations, as istic Marinobacter spp. was vibrio- the exchange of iron and carbon iron is essential for photosynthesis and ferrin (VF), a carboxylate class of has evolved between Marinobacter respiration but is present at extremely siderophore that was originally iso- spp. and marine algae. It will be a mutualistic low concentrations in sea water, owing lated from Vibrio parahaemolyticus. interesting to see whether similar partnership to its poor solubility. Marine bacteria Unlike most other siderophores mechanisms are used to support based on the have evolved to produce siderophores, that are produced by free-living other symbiotic relationships in exchange of iron which are small organic molecules marine bacteria, VF–Fe iii com- environments where iron is a scarce and carbon has that bind tightly to iron and, in doing plexes undergo extremely facile and valuable commodity. so, increase its solubility and improve photochemical oxidation, which Andrew Jermy evolved between its bioavailability. By contrast, phyto- leads to the breakdown of VF and is Marinobacter spp. plankton are not known to produce coupled with the reduction of iron oRiGiNAL REsEARCH PAPER Amin, S. A. et al. and marine algae. siderophores or indeed to take up from Fe iii to Fe ii. The Fe ii then Photolysis of iron-siderophore chelates promotes bacterial iron–siderophore dissociates from the photolysed VF bacterial-algal mutualism. Proc. Natl Acad. Sci USA 23 Sep 2009 (doi:10.1073/pnas.0905512106) complexes directly. and can be rapidly reoxidized to