Investigations of phytoplankton responses to iron stress in seawater are complicated by the fact that iron concentrations do not necessarily reflect bioavailability. Most studies to date have been based on single species or field samples and are problematic to interpret. Here, we report results from an experimental cocultivation model system that enabled us to evaluate interspecific competition as a function of iron content and form, and to study the effect of nutritional conditions on the proteomic profiles of individual species. Our study revealed that the dinoflagellate Amphidinium carterae was able to utilize iron from a hydroxamate siderophore, a strategy that could provide an ecological advantage in environments where siderophores present an important source of iron. Additionally, proteomic analysis allowed us to identify a potential candidate protein involved in iron acquisition from hydroxamate siderophores, a strategy that is largely unknown in eukaryotic phytoplankton.

• Keywords
• (s)PLS-DA, (sparse) partial least squares discriminant analysis, AUC, area under curve, Amphidinium carterae, AtpE, ATP synthase, BCS, bathocuproinedisulfonic acid disodium salt, CREG1, cellular repressor of E1A stimulated genes 1, DFOB, desferrioxamine B, EDTA, ethylenediaminetetraacetic acid, ENT, enterobactin, FACS, fluorescence-activated cell sorting, FBAI, fructose-bisphosphate aldolase I, FBAII, fructose-bisphosphate aldolase II, FBP1, putative ferrichrome-binding protein, FOB, ferrioxamine B, Flow cytometry, ISIP, iron starvation induced protein, Iron, LHCX, light-harvesting complex subunits, LL, long-term iron limitation, LR, iron enrichment, Marine microalgae, NBD, nitrobenz-2-oxa-1,3-diazole, NPQ, nonphotochemical quenching, PAGE, polyacrylamide gel electrophoresis, PSI, photosystem I, PSII, photosystem II, PetA, cytochrome b6/f, Proteomics, PsaC, photosystem I iron-sulfur center, PsaD, photosystem I reaction center subunit II, PsaE, photosystem I reaction center subunit IV, PsaL, photosystem I reaction center subunit XI, PsbC, photosystem II CP43 reaction center protein, PsbV, cytochrome c-550, RR, long-term iron sufficiency, SOD1, superoxide dismutase [Cu-Zn], Siderophores,
• Publication type
• Journal Article MeSH

Assembly of photosystem II (PSII), a water-splitting catalyst in chloroplasts and cyanobacteria, requires numerous auxiliary proteins which promote individual steps of this sequential process and transiently associate with one or more assembly intermediate complexes. In this study, we focussed on the role of a PSII-associated protein encoded by the ssl1498 gene in the cyanobacterium Synechocystis sp. PCC 6803. The N-terminal domain of this protein, which is here called Psb34, is very similar to the N-terminus of HliA/B proteins belonging to a family of high-light-inducible proteins (Hlips). Psb34 was identified in both dimeric and monomeric PSII, as well as in a PSII monomer lacking CP43 and containing Psb28. When FLAG-tagged, the protein is co-purified with these three complexes and with the PSII auxiliary proteins Psb27 and Psb28. However, the preparation also contained the oxygen-evolving enhancers PsbO and PsbV and lacked HliA/B proteins even when isolated from high-light-treated cells. The data suggest that Psb34 competes with HliA/B for the same binding site and that it is one of the components involved in the final conversion of late PSII assembly intermediates into functional PSII complexes, possibly keeping them free of Hlips. Unlike HliA/B, Psb34 does bind to the CP47 assembly module before its incorporation into PSII. Analysis of strains lacking Psb34 indicates that Psb34 mediates the optimal equilibrium of HliA/B binding among individual PSII assembly intermediates containing CP47, allowing Hlip-mediated photoprotection at all stages of PSII assembly.

• Keywords
• CP47, High-light-inducible protein, Photosynthesis, Photosystem II,
• MeSH
• Bacterial Proteins metabolism   MeSH
• Photosynthesis MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Tumor Necrosis Factor Ligand Superfamily Member 14 metabolism   MeSH
• Synechocystis * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Photosystem II Protein Complex MeSH
• Tumor Necrosis Factor Ligand Superfamily Member 14 MeSH