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Research has been conducted on Slr1295, a cyanobacterium Synechocystis sp. PCC 6803 homologue of IdiA. Results suggest that Slr1295 is a protein protecting photosystem II under iron limitation, its localization has been investigated and the study of the Slr1295-free mutant grown under iron-deficient and iron-sufficient conditions is presented.

Research has been conducted on the thylakoid membrane-associated iron-deficiency-induced protein A. The expression of this protein in Synechococcus elongatus PCC 7942 has been carried out and the results are presented.

The cyanobacterium Synechococcus sp. strain PCC 7942 contains two alkaline phosphatases (APases) that are encoded by the phoV gene. These are the phosphate-repressible 145 kDa PhoA and the phosphate-irrepressible 61.3 kDa PhoV. The presence of a second APase is probably necessary to maintain the phosphate level in the cells under conditions of stress. Characterization of the gene product reveals that PhoV has a broad pH optimum, requires Zn2+ for activity and has a wide substrate specificity. Mn2+ and phosphate inhibit the protein.

Abstract Background So far very limited knowledge exists on L-arginine catabolism in cyanobacteria, although six major L-arginine-degrading pathways have been described for prokaryotes. Thus, we have performed a bioinformatic analysis of possible L-arginine-degrading pathways in cyanobacteria. Further, we chose Synechocystis sp. PCC 6803 for a more detailed bioinformatic analysis and for validation of the bioinformatic predictions on L-arginine catabolism with a transcript analysis. Results We have evaluated 24 cyanobacterial genomes of freshwater or marine strains for the presence of putative L-arginine-degrading enzymes. We identified an L-arginine decarboxylase pathway in all 24 strains. In addition, cyanobacteria have one or two further pathways representing either an arginase pathway or L-arginine deiminase pathway or an L-arginine oxidase/dehydrogenase pathway. An L-arginine amidinotransferase pathway as a major L-arginine-degrading pathway is not likely but can not be entirely excluded. A rather unusual finding was that the cyanobacterial L-arginine deiminases are substantially larger than the enzymes in non-photosynthetic bacteria and that they are membrane-bound. A more detailed bioinformatic analysis of Synechocystis sp. PCC 6803 revealed that three different L-arginine-degrading pathways may in principle be functional in this cyanobacterium. These are (i) an L-arginine decarboxylase pathway, (ii) an L-arginine deiminase pathway, and (iii) an L-arginine oxidase/dehydrogenase pathway. A transcript analysis of cells grown either with nitrate or L-arginine as sole N-source and with an illumination of 50 μmol photons m-2 s-1 showed that the transcripts for the first enzyme(s) of all three pathways were present, but that the transcript levels for the L-arginine deiminase and the L-arginine oxidase/dehydrogenase were substantially higher than that of the three isoenzymes of L-arginine decarboxylase. Conclusion The evaluation of 24 cyanobacterial genomes revealed that five different L-arginine-degrading pathways are present in the investigated cyanobacterial species. In Synechocystis sp. PCC 6803 an L-arginine deiminase pathway and an L-arginine oxidase/dehydrogenase pathway represent the major pathways, while the L-arginine decarboxylase pathway most likely only functions in polyamine biosynthesis. The transcripts encoding the enzymes of the two major pathways were constitutively expressed with the exception of the transcript for the carbamate kinase, which was substantially up-regulated in cells grown with L-arginine.

A study was conducted to analyze the characteristics of iron-deficiency-induced protein A (idiA) in Synechococcus PCC 6301 and the DNA region surrounding idiA in Synechococcus PCC 6301 and PCC 7942. Cyanobacteria were prepared in gas wash bottles. Experimental results indicated that the absence of two gene products prevents the elevated expression of idiA under nutrient deficiency.