Iron uptake by diatoms is a biochemical process with global biogeochemical implications. In large regions of the surface ocean diatoms are both responsible for the majority of primary production and frequently experiencing iron limitation of growth. The strategies used by these phytoplankton to extract iron from seawater constrain carbon flux into higher trophic levels and sequestration into sediments. In this study we use reverse genetic techniques to target putative iron-acquisition genes in the model pennate diatom Phaeodactylum tricornutum We describe components of a reduction-dependent siderophore acquisition pathway that relies on a bacterial-derived receptor protein and provides a viable alternative to inorganic iron uptake under certain conditions. This form of iron uptake entails a close association between diatoms and siderophore-producing organisms during low-iron conditions. Homologs of these proteins are found distributed across diatom lineages, suggesting the significance of siderophore utilization by diatoms in the marine environment. Evaluation of specific proteins enables us to confirm independent iron-acquisition pathways in diatoms and characterize their preferred substrates. These findings refine our mechanistic understanding of the multiple iron-uptake systems used by diatoms and help us better predict the influence of iron speciation on taxa-specific iron bioavailability.

• Klíčová slova
• diatom, ferric reductase, iron acquisition, phytoplankton, siderophore,
• MeSH
• biologická dostupnost MeSH
• biologický transport MeSH
• CRISPR-Cas systémy MeSH
• druhová specificita MeSH
• FMN-reduktasa genetika   metabolismus   MeSH
• fylogeneze MeSH
• galium metabolismus   MeSH
• genový knockout MeSH
• klimatické změny MeSH
• membránové transportní proteiny genetika   metabolismus   MeSH
• mikrobiota MeSH
• mořská voda chemie   MeSH
• oxidace-redukce MeSH
• proteiny vnější bakteriální membrány metabolismus   MeSH
• receptory buněčného povrchu metabolismus   MeSH
• rekombinantní fúzní proteiny metabolismus   MeSH
• rozsivky genetika   růst a vývoj   metabolismus   MeSH
• siderofory metabolismus   MeSH
• železo metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• ferric citrate iron reductase MeSH Prohlížeč
• FMN-reduktasa MeSH
• galium MeSH
• membránové transportní proteiny MeSH
• proteiny vnější bakteriální membrány MeSH
• receptory buněčného povrchu MeSH
• rekombinantní fúzní proteiny MeSH
• siderofory MeSH
• siderophore receptors MeSH Prohlížeč
• železo MeSH

We investigated iron uptake mechanisms in five marine microalgae from different ecologically important phyla: the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana, the prasinophyceae Ostreococcus tauri and Micromonas pusilla, and the coccolithophore Emiliania huxleyi. Among these species, only the two diatoms were clearly able to reduce iron, via an inducible (P. tricornutum) or constitutive (T. pseudonana) ferrireductase system displaying characteristics similar to the yeast (Saccharomyces cerevisiae) flavohemoproteins proteins. Iron uptake mechanisms probably involve very different components according to the species, but the species we studied shared common features. Regardless of the presence and/or induction of a ferrireductase system, all the species were able to take up both ferric and ferrous iron, and iron reduction was not a prerequisite for uptake. Iron uptake decreased with increasing the affinity constants of iron-ligand complexes and with increasing ligand-iron ratios. Therefore, at least one step of the iron uptake mechanism involves a thermodynamically controlled process. Another step escapes to simple thermodynamic rules and involves specific and strong binding of ferric as well as ferrous iron at the cell surface before uptake of iron. Binding was paradoxically increased in iron-rich conditions, whereas uptake per se was induced in all species only after prolonged iron deprivation. We sought cell proteins loaded with iron following iron uptake. One such protein in O. tauri may be ferritin, and in P. tricornutum, Isip1 may be involved. We conclude that the species we studied have uptake systems for both ferric and ferrous iron, both involving specific iron binding at the cell surface.

• MeSH
• autoradiografie MeSH
• biologické modely MeSH
• buněčná membrána účinky léků   metabolismus   MeSH
• chelátory železa farmakologie   MeSH
• FMN-reduktasa metabolismus   MeSH
• fylogeneze MeSH
• kinetika MeSH
• ligandy MeSH
• mikrořasy účinky léků   enzymologie   růst a vývoj   metabolismus   MeSH
• oxidace-redukce účinky léků   MeSH
• Saccharomyces cerevisiae účinky léků   metabolismus   MeSH
• transport elektronů účinky léků   MeSH
• vodní organismy růst a vývoj   metabolismus   MeSH
• železo metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• chelátory železa MeSH
• ferric citrate iron reductase MeSH Prohlížeč
• FMN-reduktasa MeSH
• ligandy MeSH
• železo MeSH