The IdiA protein of Synechococcus sp. PCC 7942 functions in protecting the acceptor side of Photosystem II under oxidative stress

Synechococcus sp. strains PCC 7942 and PCC 6301 contain a 35 kDa protein called IdiA (Iron deficiency induced protein A) that is expressed in elevated amounts under Fe deficiency and to a smaller extent also under Mn deficiency. Absence of this protein was shown to mainly damage Photosystem II. To decide whether IdiA has a function in optimizing and/or protecting preferentially either the donor or acceptor side reaction of Photosystem II, a comparative analysis was performed of Synechococcus sp. PCC 7942 wild-type, the IdiA-free mutant, the previously constructed PsbO-free Synechococcus PCC 7942 mutant and a newly constructed Synechococcus PCC 7942 double mutant lacking both PsbO and IdiA. Measurements of the chlorophyll fluorescence and determinations of Photosystem II activity using a variety of electron acceptors gave evidence that IdiA has its main function in protecting the acceptor side of Photosystem II. Especially, the use of dichlorobenzoquinone, preferentially accepting electrons from Q_A, gave a decreased O₂ evolving activity in the IdiA-free mutant. Investigations of the influence of hydrogen peroxide treatment on cells revealed that this treatment caused a significantly higher damage of Photosystem II in the IdiA-free mutant than in wild-type. These results suggest that although the IdiA protein is not absolutely required for Photosystem II activity in Synechococcus PCC 7942, it does play an important role in protecting the acceptor side against oxidative damage. This revised version was published online in June 2006 with corrections to the Cover Date.     

Heterologous expression of the gene for the ethylene-forming enzyme fromPseudomonas syringae in the cyanobacteriumSynechococcus

Summary Bioconversion of atmospheric carbon dioxide to ethylene was studied in a recombinant cyanobacterium. The gene for the ethylene-forming enzyme ofPseudomonas syringae pv.phaseolicola PK2 was cloned and expressed in the cyanobacteriumSynechococcus PCC7942 R2-SPc by use of a shuttle vector pUC303. The ethylene-forming activityin vivo ofSynechococcus PCC7942 R2-SPc that carried the gene for the ethylene-forming enzyme ofP. syringae pv.phaseolicola PK2 was one-fifth of that ofE. coli JM109 that harbored the same plasmid. The enzyme accounted for 0.021% by weight of the total soluble protein inSynechococcus PCC7942 R2-SPc.     

Immunocytochemical localization of IdiA, a protein expressed under iron or manganese limitation in the mesophilic cyanobacterium Synechococcus PCC 6301 and the thermophilic cyanobacterium Synechococcus elongatus

Iron-deficiency-induced protein A (IdiA) with a calculated molecular mass of 35 kDa has previously been shown to be essential under manganese- and iron-limiting conditions in the cyanobacteria Synechococcus PCC 6301 and PCC 7942. Studies of mutants indicated that in the absence of IdiA mainly photosystem II becomes damaged, suggesting that the major function of IdiA is in Mn and not Fe metabolism (Michel et al. 1996, Microbiology 142: 2635–2645). To further elucidate the function of IdiA, the immunocytochemical localization of IdiA in the cell was examined. These investigations provided evidence that under mild Fe deficiency IdiA is intracellularly localized and is mainly associated with the thylakoid membrane in Synechococcus PCC 6301. The protein became distributed throughout the cell under severe Fe limitation when substantial morphological changes had already occurred. For additional verification of a preferential thylakoid membrane association of IdiA, these investigations were extended to the thermophilic Synechococcus elongatus. In this cyanobacterium Mn deficiency could be obtained more rapidly than in the mesophilic Synechococcus PCC 6301 and PCC 7942, and the thylakoid membrane structure proved to be more stable under limiting growth conditions. The immunocytochemical investigations with this cyanobacterium clearly supported a thylakoid membrane association of IdiA. In addition, evidence was obtained for a localization of IdiA on the cytoplasmic side of the thylakoid membrane. All available data support a function of IdiA as an Mn-binding protein that facilitates transport of Mn via the thylakoid membrane into the lumen to provide photosystem II with Mn. A possible explanation for the observation that IdiA was not only expressed under Mn deficiency but also under Fe deficiency is given in the discussion. Received: 28 July 1997 / Accepted: 26 November 1997     

Nucleotide sequence and homology comparison of two genes of the sulfate transport operon from the cyanobacterium Synechocystis sp. PCC 6803

The genome of Synechocystis sp. PCC 6803 contains an operon with homology to the sulfate permease of other prokaryotes. We used antibodies raised against cytoplasmic membrane protein to find three genes with strong homology to sbpA, orf81 and cysT genes of the cyanobacterium Synechococcus sp. PCC 7942, Escherichia coli, Salmonella typhymurium and Marchantia polymorpha. It is likely that the permease genes are expressed and the proteins are inserted into the cytoplasmic membrane.     

EXPRESSION OF THE DETOXIFYING GENE B1 IN ES‐CHERICHIA COLI AND SYNECHOCOCCUS1

Abstract We inserted the mosquito esterase B1 gene into the expression vector pRL‐439, which possesses the strong promoter PpsbA. The recombinant plasmid pRL‐Bl was used to transform E. coli HBlOl, and the positive clones were screened on LB medium plate containing 100 mg/mL ampicillin. The results of dot blotting and Southern hybridization demonstrated that these positive clones were transformed bacteria. Western blotting indicated that esterase B1 gene had been successfully expressed under the control of the PpsbA promoter in E. coli. A shuttle verruction‐B1 (pDGBl) was constructed by inserting B1‐cDNA from pRL‐Bl into polycloning site of plasmid pDc8. PDGBl was transferred into Synechoccus sp. PCC7942 through triparental conjugal transfer. Transformed single Synechococcus sp. PCC 7942 clone was obtained by neomycin screening, and large‐scale culture in liquid medium was carried out. Results of Southern blotting proved that pWB1 was transferred into Synechococcus sp. PCC 7942.     

Transformation of the fresh water cyanobacterium Synechococcus PCC7942 with the shuttle-vector pAQ-EX1 developed for the marine cyanobacterium Synechococcus PCC7002

The transformation of the fresh water cyanobacterium Synechococcus PCC7942 with the shuttle-vector pAQ-EX1 developed for the marine cyanobacterium S. PCC7002 was examined. The S. PCC7942 cells were successfully transformed with the pAQ-EX1 vector, and the vector was stably maintained in the transformant cells.     

Cyanobacteria carrying ansmt-lux transcriptional fusion as biosensors for the detection of heavy metal cations

The metal-responsivesmt operator/promoter region ofSynechococcus PCC7942 was fused to theluxCDABE genes ofVibrio fischeri. Plasmid DNA (pJLE23) carrying this fusion conferred metal ion-inducible luminescence to transformed cyanobacteria.Synechococcus PCC7942 (pJLE23) was sensitive to ZnCl₂ concentrations within a range of 0.5–4 μM as demonstrated by induction of luminescence. Trace levels of CuSO₄, and CdCl₂ were also detected.     

Analysis of glucose-6-phosphate dehydrogenase of the cyanobacterium Synechococcus sp. PCC 7942 in the zwf mutant Escherichia coli DF214 cells

The aim of this study was to express the zwf gene of Synechococcus sp. PCC 7942 in zwf mutant Escherichia coli DF214 cells and to analyse glucose-6-phosphate dehydrogenase (G6PDH) activity. Initially, mutant cells were transformed with plasmid pNUT1 containing a Synechococcus sp. PCC 7942 zwf gene with a 1 kb upstream region that is expected to contain promoter elements. Transformant DF214 cells were not complemented by this fragment in a glucose minimal medium, nor did they exhibit statistically meaningful G6PDH activity. Therefore, the zwf gene was cloned in the lac operon to express the Zwf as a fusion protein; this yielded the construct pSG162. The pSG162 transformant E. coli DF214 cells were complemented in a glucose minimal medium, indicating that cyanobacterial Zwf protein fused with the part of LacZ′ polypeptide, enabling the cells to utilize glucose via the oxidative pentose phosphate pathway. Compared with wild-type E. coli cells, approximately ten times more G6PDH activity was measured in transformant cells. This indicated that the Synechococcus sp. PCC 7942 zwf gene was expressed under the control of the E. coli lac promoter as a fusion protein and the zwf product was converted into an active G6PDH form. Analyses was also carried out to determine whether dithiothreitol (DTT) was an in vitro reducing agent affected the enzyme activity, as was previously reported for this cyanobacterial strain. The results showed no variation in enzyme activity in the reduced assay conditions. Therefore, the zwf mutant E. coli strain DF214 was found to provide a rapid system for analysis of cyanobacterial G6PDH enzymes, but not for the redox state analysis of this enzyme.     

Characterization of a two-component signal transduction system involved in the induction of alkaline phosphatase under phosphate-limiting conditions in Synechocystis sp. PCC 6803

The gene products of sll0337 and slr0081 in Synechocystis sp. PCC 6803 have been identified as the homologues of the Escherichia coli phosphate-sensing histidine kinase PhoR and response regulator PhoB, respectively. Interruption of sll0337, the gene encoding the histidine protein kinase, by a spectinomycin-resistance cassette blocked the induction of alkaline phosphatase activity under phosphate-limiting conditions. A similar result was obtained when slr0081, the gene encoding the response regulator, was interrupted with a cassette conferring resistance to kanamycin. In addition, the phosphate-specific transport system was not up-regulated in our mutants when phosphate was limiting. Unlike other genes for bacterial phosphate-sensing two-component systems, sll0337 and slr0081 are not present in the same operon. Although there are three assignments for putative alkaline phosphatase genes in the Synechocystis sp. PCC 6803 genome, only sll0654 expression was detected by northern analysis under phosphate limitation. This gene codes for a 149 kDa protein that is homologous to the cyanobacterial alkaline phosphatase reported in Synechococcus sp. PCC 7942 [Ray, J.M., Bhaya, D., Block, M.A. and Grossman, A.R. (1991) J. Bact. 173: 4297–4309]. An alignment identified a conserved 177 amino acid domain that was found at the N-terminus of the protein encoded by sll0654 but at the C-terminus of the protein in Synechococcus sp. PCC 7942.     

Improvement of Cd2+ uptake ability of SmtA protein by Lys/Cys mutation; experimental and theoretical studies

The improved Cd²⁺ surface affinity characteristics of a mutated cyanobacterial metallothionein SmtA (K45C) were investigated via experimental and theoretical methods. Molecular dynamics simulations were carried out using a model of Cd²⁺ and other ions enclosed in a fully hydrated simulation box with the wild-type or mutated SmtA protein. The theoretical results suggested that mutated SmtA was more powerful in absorption of Cd²⁺ than the wild-type protein. Then, the mutated smtA gene (from Synechococcus PCC 7942) was synthesized by simplified gene synthesis method and expressed on isopropyl-beta-d-thiogalactopyranoside induction. The protein expression was investigated by SDS-PAGE and verified by Western blotting. Finally, cadmium uptake ratio of mutant protein toward wild type was analyzed by atomic absorption. This study is the first example of cytoplasmic expression of a mutant protein. Experimental results also verified that the mutation intensifies uptake of Cd²⁺ ions.     

Cloning and Characterization of the nrtA Gene That Encodes a 45-kDa Protein Involved in Nitrate Transport in the Cyanobacterium Synechococcus PCC 7942

A 45-kDa protein in the cytoplasmic membrane of the cyanobacteriumSynechococcus PCC 7942 is involved in the active transport ofnitrate [Omata et al. (1989) Proc. Natl. Acad. Sci. USA 86:6612]. The gene coding for this protein (designated herein asnrtA) has been cloned and sequenced. The nrtA gene encodes aprotein of 443 amino acids with a calculated molecular weightof 48424. The deduced amino acid sequence of the protein is46.5% homologous to that of a 42-kDa cytoplasmic membrane proteinthat is synthesized under carbon-limited conditions in SynechococcusPCC 7942. (Received July 16, 1990; Accepted December 5, 1990)     

Isolation and characterization of the ccmM gene required by the cyanobacterium Synechocystis PCC6803 for inorganic carbon utilization

A high CO₂-requiring mutant of Synechocystis PCC6803 (G3) capable of C_i transport but unable to utilize the intracellular C_i pool for photosynthesis was constructed. A DNA clone of 6.1 kbp that transforms the G3 mutant to the wild-type phenotype was isolated from a Synechocystis PCC6803 genomic library. Complementation test with subclones allocated the mutation site within a DNA fragment of 674 bp nucleotides. Sequencing analysis of the mutation region elucidated an open reading frame encoding a 534 amino-acid protein with a significant sequence homology to the protein coded by the ccmN gene of Synechococcus PCC7942. The ccmM-like gene product of Synechocystis PCC6803 contains four internal repeats with a week similarity to the rbcS gene product. An open reading frame homologous to the ccmN gene of Synechococcus PCC7942 was found downstream to the ccmM-like gene. As opposed to the Synechococcus PCC7942 ccmM and ccmN genes located 2 kbp upstream to, and oriented in the same direction as, the rbc operon, the ccm-like genes in Synechocystis PCC6803 are not located within 22 kbp upstream to the rbcL gene of the Rubisco operon. Thus, despite the resemblance in clustering of the ccmM and ccmN genes in both cyanobacterial species, the difference in their genomic location relative to the rbc genes demonstrates variability in structural organization of the genes involved in inorganic carbon acquisition.Abbreviations CCM CO₂-concentrating mechanism - C_i inorganic carbon - HCR high CO₂-requiring - kbp kilobase pair - ORF open reading frame - Rubisco ribulose 1,5-bisphosphate carboxylase-oxygenase gene - SSC sodium chloride and sodium citrate - WT wild-type     

Isolation and purification of siderophores produced by cyanobacteria,Synechococcus sp. PCC 7942 andAnabaena variabilis ATCC 29413

New siderophores were isolated and purified from the spent growth medium of the cyanobacteriaSynechococcus sp. PCC 7942 (Anacystis nidulans R2) andAnabaena variabilis ATCC 29413 by solvent extraction and thin-layer chromatography. For each species the siderophore was released into the medium when the cells were grown at low iron concentrations and was not found in the medium of cells grown in iron-sufficient medium. Through a series of biological and chemical tests, combined with spectral analysis, the dihydroxamate nature of each siderophore was confirmed. The siderophores produced bySynechococcus sp. PCC 7942 andA. variabilis had distinct relative molecular masses of 310–313 Da and 520–525 Da, respectively. Neither of the two strains produced Arnow-positive extracellular organics, which indicate the excretion of extracellular catechol-type siderophores.     

Transfer and replication of RSF1010-derived plasmids in several cyanobacteria of the generaSynechocystis andSynechococcus

RSF1010-derived plasmids are most efficiently transferred by conjugation to the unicellular cyanobacteriaSynechocystis strains sp. PCC6803 and PCC6714 andSynechococcus strains sp. PCC7942 and PCC6301, where they replicate autonomously, even though they contain no cyanobacterial DNA. These results are especially important in the case of the facultative heterotrophic strainSynechocystis PCC6714, which is not transformable [Mol Gen Genet 204:185, 1986]     

Photophysiological and Photosynthetic Complex Changes during Iron Starvation in Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942

Iron is an essential component in many protein complexes involved in photosynthesis, but environmental iron availability is often low as oxidized forms of iron are insoluble in water. To adjust to low environmental iron levels, cyanobacteria undergo numerous changes to balance their iron budget and mitigate the physiological effects of iron depletion. We investigated changes in key protein abundances and photophysiological parameters in the model cyanobacteria Synechococcus PCC 7942 and Synechocystis PCC 6803 over a 120 hour time course of iron deprivation. The iron stress induced protein (IsiA) accumulated to high levels within 48 h of the onset of iron deprivation, reaching a molar ratio of ∼42 IsiA : Photosystem I in Synechococcus PCC 7942 and ∼12 IsiA : Photosystem I in Synechocystis PCC 6803. Concomitantly the iron-rich complexes Cytochrome b₆f and Photosystem I declined in abundance, leading to a decrease in the Photosystem I : Photosystem II ratio. Chlorophyll fluorescence analyses showed a drop in electron transport per Photosystem II in Synechococcus, but not in Synechocystis after iron depletion. We found no evidence that the accumulated IsiA contributes to light capture by Photosystem II complexes.     

The first protein map of Synechococcus sp. strain PCC 7942

The first protein map was developed of Synechococcus sp. strain PCC 7942, a model organism for studies of photosynthesis, prokaryotic circadian rhythms, cell division, carbon-concentrating mechanisms, and adaptive responses to a variety of stresses. The proteome was analyzed by two-dimensional gel electrophoresis with subsequent MALDI-TOF mass spectroscopy and database analysis. Of the 140 analyzed protein spots, 110 were successfully identified as 62 different proteins, many of which occurred as multiple spots on the gel. The identified proteins participate in the major metabolic and cellular processes in cyanobacterial cells during the exponential growth phase. In addition, 14 proteins which were previously either unknown or considered to be hypothetical were shown to be true gene products in Synechococcus sp. strain PCC 7942. These results may be helpful for the annotation of the recently sequenced genome of this cyanobacterium, as well as for biochemical and physiological studies of Synechococcus.     

Characterization of the photosystem II 32 kDa protein in Synechococcus PCC7942

A rapidly labeled photosynthetic membrane protein was identified in the cyanobacterium Synechococcus PCC7942 R2 as the 32 kDA protein that is involved in electron transport and quinone binding in the photosystem II complex. Partial proteolysis of the membrane-bound protein indicates that the internal architecture and the topology of the Synechococcus 32 kDa protein resembles the analogous protein of higher plants. In addition to the R2 wild-type strain, we characterized three psbA-inactivated Synechococcus strains, in which two of the three endogenous psbA genes were inactivated. In all strains, a 32 kDa protein cross-reacts with an antiserum that was raised against a higher-plant 32 kDa protein and displays in vivo light-dependent turnover. In Synechococcus, the herbicide DCMU inhibits the 32 kDa protein turnover at similar concentration ranges as in higher plants; however, a fraction of the molecules always displays a DCMU-insensitive degradation.